What is the BMI formula?

BMI = weight (kg) ÷ height (m)². Convert your height from cm to m and divide twice. For example, 170 cm and 65 kg gives 65 ÷ 1.7 ÷ 1.7 = 22.49…, so your BMI is 22.5 (normal). 160 cm and 55 kg gives 21.5.

How is the standard (ideal) weight calculated?

Standard weight = height (m) × height (m) × 22. Because BMI 22 is statistically linked to the lowest risk of illness, this is called the standard, ideal, or healthy weight. For 160 cm it is 1.6 × 1.6 × 22 = 56.3 kg; for 170 cm it is 63.6 kg.

What are the standard, beauty, and Cinderella weights for 160 cm?

The standard weight (BMI 22) is 56.3 kg, the beauty weight (BMI 20) is 51.2 kg, and the Cinderella weight (BMI 18) is 46.1 kg. The normal range (BMI 18.5 to under 25) is 47.4 kg to under 64.0 kg, so the Cinderella weight is below it, in the “underweight” range. For 155 cm the standard weight is 52.9 kg and the beauty weight 48.1 kg; for 165 cm they are 59.9 kg and 54.4 kg.

At what BMI are you considered obese?

Under the Japan Society for the Study of Obesity criteria, a BMI of 25 or more is obese: under 18.5 is underweight, 18.5 to under 25 is normal, 25 to under 30 is class 1, 30 to under 35 class 2, 35 to under 40 class 3, and 40 or more class 4. The WHO international criteria call 25 or more “overweight” and 30 or more “obese”.

What are the “beauty weight” and “Cinderella weight”?

The beauty weight is the weight at BMI 20 and the Cinderella weight is the weight at BMI 18. These terms spread in Japan as a guide to looking slim, but neither is a medical standard. The Cinderella weight (BMI 18) is classed as underweight and may lead to irregular periods, lower bone density, and weaker immunity, so it is not a recommended goal.

Does the ideal BMI change with age?

Yes. Japan’s Dietary Reference Intakes (2020) set the target BMI at 18.5–24.9 for ages 18–49, 20.0–24.9 for ages 50–64, and 21.5–24.9 for 65 and over. The lower limit rises with age to prevent muscle loss and frailty caused by being underweight. Enter your age to see whether you are in this range.

How is basal metabolic rate calculated?

This tool uses the National Institute of Health and Nutrition formula, built from Japanese measurement data. For men: (0.0481 × weight kg + 0.0234 × height cm − 0.0138 × age − 0.4235) × 1000 ÷ 4.186; for women the last constant is 0.9708. A 30-year-old woman at 160 cm and 55 kg gets about 1,196 kcal; a 40-year-old man at 170 cm and 70 kg gets about 1,522 kcal. Results from other formulas such as Harris–Benedict are shown alongside.

How is daily calorie burn calculated?

Daily calorie burn (estimated energy requirement) = basal metabolic rate × physical activity level. The activity level is 1.50 for mostly desk work without exercise, 1.75 for people who move around commuting or doing housework, and 2.00 for standing jobs or regular exercise. A 30-year-old woman at 160 cm and 55 kg with “moderate” activity burns about 1,196 kcal × 1.75 ≈ 2,092 kcal.

How many kcal do I need to cut to lose 1 kg of fat?

About 7,200 kcal. Body fat tissue is about 80% fat, and 1 g of fat is about 9 kcal, so 1,000 g × 0.8 × 9 kcal = 7,200 kcal. Losing 1 kg in a month (30 days) means 240 kcal a day; losing 5 kg in three months means 400 kcal a day, through eating less or burning more.

How much weight loss per month is healthy?

A common guide is up to 5% of body weight per month, and about 2–3% is easier to sustain. For someone weighing 60 kg that is about 1.2–1.8 kg a month. Losing faster tends to cost muscle, lower your metabolism, and make rebound more likely. The “Target weight & diet” tab shows your monthly loss as a percentage of body weight and warns you when the pace is too fast.

How many kcal a day should I eat to lose 5 kg in three months?

5 kg × 7,200 kcal ÷ 90 days = a 400 kcal daily deficit. A 30-year-old woman at 160 cm and 60 kg with “moderate” activity burns about 2,193 kcal a day, so the intake target is about 1,793 kcal. Burning all 400 kcal by walking would take about two and a half hours a day, so splitting it between diet and exercise is more realistic.

I have a lot of muscle but BMI says I’m obese.

BMI uses only height and weight, so it cannot tell muscle from fat. Muscle is heavier than fat, so people who train often have a BMI over 25 with little body fat. To understand your body composition, measure body fat with a body composition scale, or also check your waist circumference (85 cm or more for men and 90 cm or more for women is the Japanese guide for visceral obesity).

What are the Kaup and Rohrer indexes?

Both measure children’s build. The Kaup index is for infants from about 3 months to 5 years: weight (kg) ÷ height (cm)² × 10,000 (the same calculation as BMI), with 15–19 as “normal”. The Rohrer index is for elementary and junior high school children: weight (kg) ÷ height (cm)³ × 10,000,000, with 115–145 as “normal”. A 75 cm, 10 kg infant has a Kaup index of 17.8, and a 130 cm, 27 kg child has a Rohrer index of 123 — both “normal”.

BMI Calculator & Healthy Weight (Standard Weight, BMR)

Enter your height and weight to get your BMI and obesity class (Japan Society for the Study of Obesity criteria), plus the gap between your weight and the standard weight (BMI 22), the “beauty weight” (BMI 20), and the “Cinderella weight”. Add age and sex to see your basal metabolic rate and daily calorie burn, or a target weight and period to see how many kcal to cut per day. Kaup and Rohrer indexes for children are included too.

ABOUT

About BMI Calculator & Healthy Weight (Standard Weight, BMR)

The BMI & Healthy Weight Calculator works out your BMI (body mass index) and obesity class from your height and weight, and shows how far you are from the standard weight (BMI 22), the “beauty weight” (BMI 20), and the “Cinderella weight” (BMI 18). Classes follow the Japan Society for the Study of Obesity (under 18.5 is underweight, 25 or more is obese), and entering your age compares you with the age-based target BMI from Japan’s Dietary Reference Intakes (2020). Add sex, age, and activity level to get your basal metabolic rate and daily calorie burn, or a target weight and period to see how many kcal to cut per day, your intake target, and whether the pace is reasonable. Kaup index for infants and Rohrer index for school children are supported too.

How to use BMI Calculator & Healthy Weight (Standard Weight, BMR)

1On the “BMI & healthy weight” tab, enter your height and weight (either “1.6 m” or “160 cm” works)
2Check your BMI, your obesity class, and the gap between your weight and the standard weight / normal range
3Enter your age to see whether you are within the target BMI range for your age group
4On the “BMR & calories” tab, choose sex, age, and activity level to see your basal metabolic rate and daily calorie burn
5On the “Target weight & diet” tab, enter a goal weight and period to see your daily intake target and pace
6For children, use the “Children (Kaup / Rohrer)” tab and choose infant or school-age

Great for

Check whether your BMI from a health check is in the normal range or obese
Find the standard weight and beauty weight for a height of 160 cm
See how many kg you need to lose (or gain) to reach the standard weight
Compare standard and beauty weights in a chart by height
Check the target BMI range for people in their 50s or 60s
Calculate your basal metabolic rate and daily calorie burn
Work out how many kcal per day to eat to lose 5 kg in three months
Check whether your diet plan is too aggressive based on the monthly pace
Calculate a baby’s Kaup index or a school child’s Rohrer index

Good to know

BMI is calculated as weight (kg) ÷ height (m) ÷ height (m). To keep the display and the class consistent, the class is based on the value rounded to one decimal place.
Obesity classes follow the Japan Society for the Study of Obesity (under 18.5: underweight; 18.5 to under 25: normal; 25 to under 30: obese class 1; 30 to under 35: class 2; 35 to under 40: class 3; 40 or more: class 4). The WHO treats 30 or more as obese, so the Japanese criteria are stricter.
BMI uses only height and weight, so it cannot tell muscle from fat. Muscular athletes may be classed as “obese” even with little body fat.
The beauty weight (BMI 20) and Cinderella weight (BMI 18) are not medical standards. BMI 18 in particular is “underweight” and is not a healthy goal.
Age-based target BMIs come from Japan’s Dietary Reference Intakes (2020): ages 18–49: 18.5–24.9, 50–64: 20.0–24.9, 65 and over: 21.5–24.9.
Basal metabolic rate is based on the National Institute of Health and Nutrition formula (Ganpule et al.), which was built from Japanese measurement data. Results from the reference-value method, the Harris–Benedict equation, and the Mifflin–St Jeor equation are shown side by side.
Daily calorie burn is basal metabolic rate × physical activity level. Activity levels follow the Dietary Reference Intakes (ages 18–64: low 1.50, moderate 1.75, high 2.00; slightly lower values from 65).
Diet calculations assume about 7,200 kcal per kg of body fat and a 30-day month. In reality water and muscle also change, so weight does not drop in a straight line.
People under 18, pregnant or breastfeeding, or on a medically restricted diet need different standards. Results are not a medical diagnosis.
Everything you enter is calculated in your browser and is never sent to a server.

Questions this tool answers

Use BMI Calculator & Healthy Weight (Standard Weight, BMR) for searches like these:

calculate my BMI from height and weight
check whether my BMI is normal or obese
know the standard weight for 160 cm
find my beauty weight or Cinderella weight
see how many kg I need to lose to reach my standard weight
see a healthy weight chart by height
find the weight for a BMI of 22 or 25
know the ideal BMI for people in their 50s or 60s
calculate my basal metabolic rate
know how many calories I burn per day
know how many calories to eat while dieting
know how many kcal to cut to lose 2 kg in a month
know how many kcal are in 1 kg of fat
calculate a baby’s Kaup index
calculate a child’s Rohrer index

FAQ

What is the BMI formula?: BMI = weight (kg) ÷ height (m)². Convert your height from cm to m and divide twice. For example, 170 cm and 65 kg gives 65 ÷ 1.7 ÷ 1.7 = 22.49…, so your BMI is 22.5 (normal). 160 cm and 55 kg gives 21.5.
How is the standard (ideal) weight calculated?: Standard weight = height (m) × height (m) × 22. Because BMI 22 is statistically linked to the lowest risk of illness, this is called the standard, ideal, or healthy weight. For 160 cm it is 1.6 × 1.6 × 22 = 56.3 kg; for 170 cm it is 63.6 kg.
What are the standard, beauty, and Cinderella weights for 160 cm?: The standard weight (BMI 22) is 56.3 kg, the beauty weight (BMI 20) is 51.2 kg, and the Cinderella weight (BMI 18) is 46.1 kg. The normal range (BMI 18.5 to under 25) is 47.4 kg to under 64.0 kg, so the Cinderella weight is below it, in the “underweight” range. For 155 cm the standard weight is 52.9 kg and the beauty weight 48.1 kg; for 165 cm they are 59.9 kg and 54.4 kg.
At what BMI are you considered obese?: Under the Japan Society for the Study of Obesity criteria, a BMI of 25 or more is obese: under 18.5 is underweight, 18.5 to under 25 is normal, 25 to under 30 is class 1, 30 to under 35 class 2, 35 to under 40 class 3, and 40 or more class 4. The WHO international criteria call 25 or more “overweight” and 30 or more “obese”.
What are the “beauty weight” and “Cinderella weight”?: The beauty weight is the weight at BMI 20 and the Cinderella weight is the weight at BMI 18. These terms spread in Japan as a guide to looking slim, but neither is a medical standard. The Cinderella weight (BMI 18) is classed as underweight and may lead to irregular periods, lower bone density, and weaker immunity, so it is not a recommended goal.
Does the ideal BMI change with age?: Yes. Japan’s Dietary Reference Intakes (2020) set the target BMI at 18.5–24.9 for ages 18–49, 20.0–24.9 for ages 50–64, and 21.5–24.9 for 65 and over. The lower limit rises with age to prevent muscle loss and frailty caused by being underweight. Enter your age to see whether you are in this range.
How is basal metabolic rate calculated?: This tool uses the National Institute of Health and Nutrition formula, built from Japanese measurement data. For men: (0.0481 × weight kg + 0.0234 × height cm − 0.0138 × age − 0.4235) × 1000 ÷ 4.186; for women the last constant is 0.9708. A 30-year-old woman at 160 cm and 55 kg gets about 1,196 kcal; a 40-year-old man at 170 cm and 70 kg gets about 1,522 kcal. Results from other formulas such as Harris–Benedict are shown alongside.
How is daily calorie burn calculated?: Daily calorie burn (estimated energy requirement) = basal metabolic rate × physical activity level. The activity level is 1.50 for mostly desk work without exercise, 1.75 for people who move around commuting or doing housework, and 2.00 for standing jobs or regular exercise. A 30-year-old woman at 160 cm and 55 kg with “moderate” activity burns about 1,196 kcal × 1.75 ≈ 2,092 kcal.
How many kcal do I need to cut to lose 1 kg of fat?: About 7,200 kcal. Body fat tissue is about 80% fat, and 1 g of fat is about 9 kcal, so 1,000 g × 0.8 × 9 kcal = 7,200 kcal. Losing 1 kg in a month (30 days) means 240 kcal a day; losing 5 kg in three months means 400 kcal a day, through eating less or burning more.
How much weight loss per month is healthy?: A common guide is up to 5% of body weight per month, and about 2–3% is easier to sustain. For someone weighing 60 kg that is about 1.2–1.8 kg a month. Losing faster tends to cost muscle, lower your metabolism, and make rebound more likely. The “Target weight & diet” tab shows your monthly loss as a percentage of body weight and warns you when the pace is too fast.
How many kcal a day should I eat to lose 5 kg in three months?: 5 kg × 7,200 kcal ÷ 90 days = a 400 kcal daily deficit. A 30-year-old woman at 160 cm and 60 kg with “moderate” activity burns about 2,193 kcal a day, so the intake target is about 1,793 kcal. Burning all 400 kcal by walking would take about two and a half hours a day, so splitting it between diet and exercise is more realistic.
I have a lot of muscle but BMI says I’m obese.: BMI uses only height and weight, so it cannot tell muscle from fat. Muscle is heavier than fat, so people who train often have a BMI over 25 with little body fat. To understand your body composition, measure body fat with a body composition scale, or also check your waist circumference (85 cm or more for men and 90 cm or more for women is the Japanese guide for visceral obesity).
What are the Kaup and Rohrer indexes?: Both measure children’s build. The Kaup index is for infants from about 3 months to 5 years: weight (kg) ÷ height (cm)² × 10,000 (the same calculation as BMI), with 15–19 as “normal”. The Rohrer index is for elementary and junior high school children: weight (kg) ÷ height (cm)³ × 10,000,000, with 115–145 as “normal”. A 75 cm, 10 kg infant has a Kaup index of 17.8, and a 130 cm, 27 kg child has a Rohrer index of 123 — both “normal”.

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