How is electricity cost calculated?

It is power consumption (kW) × usage time (h) × price per kWh (yen). Power is often written in W, so divide by 1000 to get kW. For example, a 1,200 W hair dryer used for 10 minutes (0.17 hours) is 1.2 kW × 0.17 h = about 0.2 kWh, which is about 6.2 yen at 31 yen/kWh. This tool shows the formula as it goes, so you can check it afterwards.

How many yen is 1 kWh?

For appliance electricity costs, 31 yen/kWh is used as the nationwide guideline (the guideline unit price for new electricity rates of the Electric Home Appliance Fair Trade Council, revised from 27 yen in July 2022). In an actual bill, however, base charges, the fuel cost adjustment and the renewable energy levy are added, so dividing the bill by the usage can give around 40 yen. The "Look up from your bill" tab works out your own rate.

How much does a 1000 W appliance cost to run for one hour?

1,000 W = 1 kW, so one hour uses 1 kWh. At 31 yen/kWh that is 31 yen per hour. Likewise 500 W is 15.5 yen and 1,200 W is 37.2 yen. It is a simple proportion: double the wattage and the cost doubles, halve the time and the cost halves.

How much does an air conditioner cost per hour?

A 6–8 tatami mat air conditioner uses around 400 W for cooling, about 12.4 yen per hour. Heating uses more because the difference from the outside temperature is larger, around 500 W and about 15.5 yen. A 14 tatami mat living-room air conditioner is about 24.8 yen for cooling and about 31 yen for heating. Using it 8 hours a day for 30 days is roughly 3,000 yen for cooling and 3,700 yen for heating.

Is it cheaper to leave the air conditioner on or to switch it off often?

Judged by power consumption alone, leaving it on for 24 hours (400 W) costs about 8,900 yen a month, while running it only the 12 hours you are home costs about 4,500 yen, so switching it off is cheaper. However, an air conditioner uses 2 to 3 times its rating for roughly the first 30 minutes of running, so for an outing of 30 minutes to an hour it is often cheaper not to switch it off. As a rule of thumb: switch it off for outings of an hour or more, and leave it on for shorter ones.

Which is cheapest: a kotatsu, an electric blanket or an electric carpet?

Used 5–8 hours a day, the monthly guideline is about 370 yen for an electric blanket (50 W, 8 hours), about 700 yen for a kotatsu (150 W, 5 hours), about 1,860 yen for a 2 tatami mat electric carpet (400 W, 5 hours) and about 5,580 yen for an oil-filled radiator (1,200 W, 5 hours). The closer to the body the heating is, the cheaper it gets. To warm a whole room, an air conditioner is the most efficient, needing less than half the electricity of a ceramic fan heater for the same heat.

How much does a hair dryer or microwave cost to use?

A hair dryer (1,200 W) used for 10 minutes costs about 6.2 yen, or about 190 yen a month if used every day. A microwave is similar, about 6.2 yen for 10 minutes of heating. Boiling 1 L in an electric kettle (1,250 W) costs about 3.9 yen. These are among the highest wattages in the home, but they run for only a few minutes, so the monthly amount is small. What drives the cost is wattage × time, not wattage alone.

How much does a refrigerator cost per month?

A recent 400 L-class model (about 300 kWh a year, average 34 W) costs about 760 yen a month and about 9,100 yen a year. A same-class model from more than 10 years ago (about 570 kWh a year, average 65 W) costs about 1,450 yen a month and about 17,400 yen a year, a difference of over 8,000 yen a year. Because it runs 24 hours a day, 365 days a year, it is one of the biggest consumers per unit in a home.

Which is cheaper, a bathroom dryer or a washer-dryer?

Drying for 3 hours in a bathroom dryer (1,250 W) costs about 116 yen per use, or about 3,500 yen a month if used every day. A heat-pump drum washer-dryer uses about 1 kWh, about 33 yen, per load, or about 980 yen a month, a difference of around 2,500 yen a month. A heater-type washer-dryer uses about 2.1 kWh, about 65 yen, per load, which falls between the bathroom dryer and the drum type.

How much does standby power cost?

According to a survey by the Agency for Natural Resources and Energy, standby consumption is about 5% of a household's total, roughly 228 kWh a year. At 31 yen/kWh that is about 7,000 yen a year. Per device, though, 1 W of standby power is only about 270 yen a year. Unplugging pays off most for devices that are always heating rather than merely on standby, such as storage-tank bidet toilet seats and electric pots that keep water hot for long periods.

What is the difference between power (W) and energy (kWh)?

W is how much electricity is being used at that moment, and kWh is that multiplied by how many hours it continues. You are charged for kWh. A 1,000 W appliance used for one hour uses 1 kWh, and a 100 W appliance used for 10 hours also uses 1 kWh, so the cost is the same. The usage on your meter reading slip is also in kWh.

Does lowering the contract amperage reduce the electricity cost?

The base charge goes down. For Juryo Dento B of Tokyo Electric Power Energy Partner (東京電力エナジーパートナー), it is about 31 yen (tax included) per ampere, so dropping from 40 A to 30 A saves about 312 yen a month and about 3,700 yen a year. However, the power you can use at the same time becomes smaller and the breaker trips more easily. It is safer not to lower it in a household that runs a microwave, hair dryer and air conditioner at the same time. In regions without an ampere-based system, such as Kansai, Chugoku and Shikoku Electric Power areas, this method is not available.

What are the renewable energy levy and the fuel cost adjustment?

The renewable energy levy (renewable energy power promotion levy) is money everyone pays according to their usage to cover the purchase cost of electricity generated by solar and other sources; it is uniform nationwide and revised every May. It is 3.98 yen/kWh for fiscal 2025. The fuel cost adjustment reflects monthly changes in the price of fuels used for generation (LNG, coal, crude oil) in your bill, and becomes negative (a discount) when fuel is cheap. Both are calculated as usage times a rate.

What is the average electricity cost for living alone?

Typical monthly usage is about 185 kWh for a one-person household, about 271 kWh for two people, about 313 kWh for three and about 327 kWh for four. Calculated with Juryo Dento B, 30 A and the renewable energy levy included, that is about 7,600 yen for living alone and about 13,500 yen for four people. Because of heating and cooling, though, months differ greatly: the most expensive winter bills (February–March) are about 30% higher than the yearly average. All-electric homes and insulation also change the figure a lot.

Why did my electricity bill suddenly go up?

First compare the usage (kWh) on your meter reading slip with the previous month and the same month last year. If usage has risen, heating and cooling is the cause. Because meter readings bill the previous month, midwinter use shows up on the February–March bills and midsummer use on the September bill. The winter peak is about 30% above the yearly average even with the same lifestyle. If usage has not changed but the amount has, the cause is a rise in the fuel cost adjustment, a revision of the renewable energy levy (every May), the end of subsidies, or a change in the plan's rates. Rebuilding the bill from the usage in this tool lets you separate which is responsible.

Why doesn't the calculated result match my actual bill?

There are mainly three reasons. First, the rate: the default 31 yen/kWh is a guideline, which differs from the real rate including base charges and levies. Second, power consumption: appliances do not run at a constant wattage, and air conditioners and refrigerators change their running intensity moment by moment. Third, the estimate of usage time. To get closer to your bill, enter the effective price worked out on the "Look up from your bill" tab in the shared settings.

Where should I start to reduce my electricity cost?

The quick reference table is sorted by monthly amount, largest first, so reviewing the items at the top is the shortcut. In most homes, air conditioning, hot water, the refrigerator and lighting account for most of the usage. The biggest effects come from setting the air conditioner 1°C more leniently, cleaning the filter, switching lighting to LED, replacing a refrigerator that is over 10 years old, and stopping use of the bathroom dryer. On the other hand, unplugging a phone charger or Wi-Fi router changes the bill by only a few to a few dozen yen a month.

Electricity Cost Calculator (by Appliance, from Wattage per Hour / Day / Month)

Choose from 48 appliances such as air conditioners, kotatsu, hair dryers and dishwashers, or just enter the power consumption (W) and usage time to calculate the electricity cost per hour, day, month and year. You can also see the difference between leaving something on and switching it off often, compare incandescent bulbs with LEDs, and find out how many years it takes to recover a replacement cost. From the usage on your meter reading slip, it builds the breakdown of base charge, 3-tier energy charge, fuel cost adjustment and renewable energy levy, works out the effective price per kWh in your own home, and applies it to the per-appliance calculations.

ABOUT

About Electricity Cost Calculator (by Appliance, from Wattage per Hour / Day / Month)

The Electricity Cost Calculator works out the electricity cost per hour, day, month and year when you pick an appliance or enter its power consumption (W). It comes with typical power consumption and usage figures for 48 appliances such as air conditioners, kotatsu, hair dryers, dishwashers and bathroom dryers, so you can just select one and calculate. It can also compare leaving something on for 24 hours with using it for only 12, or the difference when swapping an incandescent bulb for an LED together with how long it takes to recover the purchase cost, and from the usage on your meter reading slip it builds the breakdown of base charge, 3-tier energy charge, fuel cost adjustment and renewable energy levy. You can also work out the effective price per kWh in your own home from the bill amount and usage and apply it to the per-appliance calculations. The default rate is 31 yen/kWh, the guideline price also used in appliance catalogs.

How to use Electricity Cost Calculator (by Appliance, from Wattage per Hour / Day / Month)

1On the "Calculate by appliance" tab, choose the appliance you want to check from the list (typical power and usage time are filled in)
2Overwrite the power (W), hours per day and days per month to match your own model and habits
3Check the electricity cost per hour, day, month and year, and the energy used (kWh)
4For an appliance not in the list, enter the wattage printed on the unit directly on the "Calculate from wattage" tab
5On the "Compare electricity costs" tab, line up leaving it on versus switching it off, or models before and after a replacement, to see the difference
6For an accurate figure, enter the usage and bill amount from your meter reading slip on the "Look up from your bill" tab and apply the resulting effective price to the shared settings

Great for

Find out how much it costs to run an air conditioner for one hour
Check the monthly difference between leaving the air conditioner on and switching it off often
Compare which heater is cheapest among a kotatsu, electric blanket, electric carpet and oil-filled radiator
Decide whether a bathroom dryer or a washer-dryer is cheaper for drying laundry
Calculate in how many years the price of a new refrigerator is recovered through the electricity savings
Judge whether replacing incandescent bulbs with LED bulbs is worth it, in terms of money and payback period
Check whether the amount on your meter reading slip is reasonable for the usage by rebuilding the breakdown
See whether your household's electricity use is high or low compared with households of the same size
Estimate how much more electricity costs when you use a PC and air conditioner while working from home

Good to know

The default rate of 31 yen/kWh is the "guideline unit price for new electricity rates" (updated July 2022) set by the Electric Home Appliance Fair Trade Council (全国家庭電気製品公正取引協議会). Appliance maker catalogs and store displays use the same price, so amounts are easy to compare with other sites.
The amount you actually pay per kWh can be around 40 yen once base charges and the renewable energy levy are included. For an accurate figure, work out bill amount ÷ usage on the "Look up from your bill" tab and enter that rate in the shared settings.
Appliance power consumption uses values close to the average while running, not the "rated (maximum)" figure in catalogs, because calculating with the rating would give several times the real cost. Values vary by model, so overwrite them with the wattage on your unit or manual.
An air conditioner uses 2 to 3 times its rating right after it starts and drops sharply once it reaches the set temperature. Because the calculation uses the average power, short periods of use come out cheaper than in reality.
The "500 W" of a microwave is its heating output, not the power drawn from the outlet. Even a 500 W output model consumes around 1,200 W. Enter the power consumption in this tool.
The energy-charge rates (tier 1: 29.80 yen, tier 2: 36.40 yen, tier 3: 40.49 yen) and the base charge default to Juryo Dento B of Tokyo Electric Power Energy Partner (東京電力エナジーパートナー). They differ by utility company, plan and fiscal year, so you can overwrite them with the rates on your meter reading slip.
The default renewable energy levy of 3.98 yen/kWh is the rate for fiscal 2025 (Reiwa 7). It is uniform nationwide and revised every May. The fuel cost adjustment changes every month and can be negative.
Night-time plans for all-electric homes and time-of-use or market-linked plans are not supported. Their rates differ by time of day, so enter an average rate in the shared settings.
Everything you enter is calculated in your browser and is not sent to a server.

Questions this tool answers

Use Electricity Cost Calculator (by Appliance, from Wattage per Hour / Day / Month) for searches like these:

I want to know how much an appliance costs per hour, day and month
I want to calculate electricity cost from power consumption (W)
I want to know the cost of using a 1000 W appliance for one hour
I want to know the air conditioner's electricity cost per hour
I want to decide whether to leave the air conditioner on or switch it off often
I want to compare the electricity costs of a kotatsu, electric blanket and electric carpet
I want to check the electricity cost of a hair dryer or microwave
I want to know a refrigerator's electricity cost per month
I want to compare whether a bathroom dryer or a washer-dryer is cheaper
I want to calculate in how many years a replacement appliance pays for itself
I want to know the savings from replacing incandescent bulbs with LEDs
I want to know how many yen 1 kWh is and find my own rate
I want to check the breakdown of my bill amount
I want to compare with the average electricity cost for living alone
I want to find out why my electricity bill suddenly went up
I want to know how much standby power costs per year
I want to know how much lowering the contract amperage would reduce the cost

FAQ

How is electricity cost calculated?: It is power consumption (kW) × usage time (h) × price per kWh (yen). Power is often written in W, so divide by 1000 to get kW. For example, a 1,200 W hair dryer used for 10 minutes (0.17 hours) is 1.2 kW × 0.17 h = about 0.2 kWh, which is about 6.2 yen at 31 yen/kWh. This tool shows the formula as it goes, so you can check it afterwards.
How many yen is 1 kWh?: For appliance electricity costs, 31 yen/kWh is used as the nationwide guideline (the guideline unit price for new electricity rates of the Electric Home Appliance Fair Trade Council, revised from 27 yen in July 2022). In an actual bill, however, base charges, the fuel cost adjustment and the renewable energy levy are added, so dividing the bill by the usage can give around 40 yen. The "Look up from your bill" tab works out your own rate.
How much does a 1000 W appliance cost to run for one hour?: 1,000 W = 1 kW, so one hour uses 1 kWh. At 31 yen/kWh that is 31 yen per hour. Likewise 500 W is 15.5 yen and 1,200 W is 37.2 yen. It is a simple proportion: double the wattage and the cost doubles, halve the time and the cost halves.
How much does an air conditioner cost per hour?: A 6–8 tatami mat air conditioner uses around 400 W for cooling, about 12.4 yen per hour. Heating uses more because the difference from the outside temperature is larger, around 500 W and about 15.5 yen. A 14 tatami mat living-room air conditioner is about 24.8 yen for cooling and about 31 yen for heating. Using it 8 hours a day for 30 days is roughly 3,000 yen for cooling and 3,700 yen for heating.
Is it cheaper to leave the air conditioner on or to switch it off often?: Judged by power consumption alone, leaving it on for 24 hours (400 W) costs about 8,900 yen a month, while running it only the 12 hours you are home costs about 4,500 yen, so switching it off is cheaper. However, an air conditioner uses 2 to 3 times its rating for roughly the first 30 minutes of running, so for an outing of 30 minutes to an hour it is often cheaper not to switch it off. As a rule of thumb: switch it off for outings of an hour or more, and leave it on for shorter ones.
Which is cheapest: a kotatsu, an electric blanket or an electric carpet?: Used 5–8 hours a day, the monthly guideline is about 370 yen for an electric blanket (50 W, 8 hours), about 700 yen for a kotatsu (150 W, 5 hours), about 1,860 yen for a 2 tatami mat electric carpet (400 W, 5 hours) and about 5,580 yen for an oil-filled radiator (1,200 W, 5 hours). The closer to the body the heating is, the cheaper it gets. To warm a whole room, an air conditioner is the most efficient, needing less than half the electricity of a ceramic fan heater for the same heat.
How much does a hair dryer or microwave cost to use?: A hair dryer (1,200 W) used for 10 minutes costs about 6.2 yen, or about 190 yen a month if used every day. A microwave is similar, about 6.2 yen for 10 minutes of heating. Boiling 1 L in an electric kettle (1,250 W) costs about 3.9 yen. These are among the highest wattages in the home, but they run for only a few minutes, so the monthly amount is small. What drives the cost is wattage × time, not wattage alone.
How much does a refrigerator cost per month?: A recent 400 L-class model (about 300 kWh a year, average 34 W) costs about 760 yen a month and about 9,100 yen a year. A same-class model from more than 10 years ago (about 570 kWh a year, average 65 W) costs about 1,450 yen a month and about 17,400 yen a year, a difference of over 8,000 yen a year. Because it runs 24 hours a day, 365 days a year, it is one of the biggest consumers per unit in a home.
Which is cheaper, a bathroom dryer or a washer-dryer?: Drying for 3 hours in a bathroom dryer (1,250 W) costs about 116 yen per use, or about 3,500 yen a month if used every day. A heat-pump drum washer-dryer uses about 1 kWh, about 33 yen, per load, or about 980 yen a month, a difference of around 2,500 yen a month. A heater-type washer-dryer uses about 2.1 kWh, about 65 yen, per load, which falls between the bathroom dryer and the drum type.
How much does standby power cost?: According to a survey by the Agency for Natural Resources and Energy, standby consumption is about 5% of a household's total, roughly 228 kWh a year. At 31 yen/kWh that is about 7,000 yen a year. Per device, though, 1 W of standby power is only about 270 yen a year. Unplugging pays off most for devices that are always heating rather than merely on standby, such as storage-tank bidet toilet seats and electric pots that keep water hot for long periods.
What is the difference between power (W) and energy (kWh)?: W is how much electricity is being used at that moment, and kWh is that multiplied by how many hours it continues. You are charged for kWh. A 1,000 W appliance used for one hour uses 1 kWh, and a 100 W appliance used for 10 hours also uses 1 kWh, so the cost is the same. The usage on your meter reading slip is also in kWh.
Does lowering the contract amperage reduce the electricity cost?: The base charge goes down. For Juryo Dento B of Tokyo Electric Power Energy Partner (東京電力エナジーパートナー), it is about 31 yen (tax included) per ampere, so dropping from 40 A to 30 A saves about 312 yen a month and about 3,700 yen a year. However, the power you can use at the same time becomes smaller and the breaker trips more easily. It is safer not to lower it in a household that runs a microwave, hair dryer and air conditioner at the same time. In regions without an ampere-based system, such as Kansai, Chugoku and Shikoku Electric Power areas, this method is not available.
What are the renewable energy levy and the fuel cost adjustment?: The renewable energy levy (renewable energy power promotion levy) is money everyone pays according to their usage to cover the purchase cost of electricity generated by solar and other sources; it is uniform nationwide and revised every May. It is 3.98 yen/kWh for fiscal 2025. The fuel cost adjustment reflects monthly changes in the price of fuels used for generation (LNG, coal, crude oil) in your bill, and becomes negative (a discount) when fuel is cheap. Both are calculated as usage times a rate.
What is the average electricity cost for living alone?: Typical monthly usage is about 185 kWh for a one-person household, about 271 kWh for two people, about 313 kWh for three and about 327 kWh for four. Calculated with Juryo Dento B, 30 A and the renewable energy levy included, that is about 7,600 yen for living alone and about 13,500 yen for four people. Because of heating and cooling, though, months differ greatly: the most expensive winter bills (February–March) are about 30% higher than the yearly average. All-electric homes and insulation also change the figure a lot.
Why did my electricity bill suddenly go up?: First compare the usage (kWh) on your meter reading slip with the previous month and the same month last year. If usage has risen, heating and cooling is the cause. Because meter readings bill the previous month, midwinter use shows up on the February–March bills and midsummer use on the September bill. The winter peak is about 30% above the yearly average even with the same lifestyle. If usage has not changed but the amount has, the cause is a rise in the fuel cost adjustment, a revision of the renewable energy levy (every May), the end of subsidies, or a change in the plan's rates. Rebuilding the bill from the usage in this tool lets you separate which is responsible.
Why doesn't the calculated result match my actual bill?: There are mainly three reasons. First, the rate: the default 31 yen/kWh is a guideline, which differs from the real rate including base charges and levies. Second, power consumption: appliances do not run at a constant wattage, and air conditioners and refrigerators change their running intensity moment by moment. Third, the estimate of usage time. To get closer to your bill, enter the effective price worked out on the "Look up from your bill" tab in the shared settings.
Where should I start to reduce my electricity cost?: The quick reference table is sorted by monthly amount, largest first, so reviewing the items at the top is the shortcut. In most homes, air conditioning, hot water, the refrigerator and lighting account for most of the usage. The biggest effects come from setting the air conditioner 1°C more leniently, cleaning the filter, switching lighting to LED, replacing a refrigerator that is over 10 years old, and stopping use of the bathroom dryer. On the other hand, unplugging a phone charger or Wi-Fi router changes the bill by only a few to a few dozen yen a month.

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