How to Calculate a Dilution Ratio: How Much Concentrate for 1:1000, and Why 10× Is Not 1 Part to 10 Parts Water
A label says "dilute 1000 times", but how many millilitres of concentrate go into 2 litres of water? It rarely comes to mind straight away. Detergents add another notation, "1 part concentrate to 10 parts water", and the same "10×" can mean different amounts. This guide explains what a dilution ratio means and the formula behind it, how the calculation changes depending on whether you fix the final volume, the water or the concentrate, the difference between the two ways of counting, and tips for measuring very small amounts of concentrate accurately.
What a dilution ratio means: 1000× means the final liquid is 1000 times the concentrate
A dilution ratio (or dilution factor) tells you how many times larger the diluted liquid is than the concentrate you started with. When the label on a pesticide, liquid fertiliser or plant tonic says 1000×, it means you add water to 1 ml of concentrate until the total is 1000 ml. The key point is that you add 999 ml of water, not 1000 ml.
For example, to make 2 L (2000 ml) at 1000×, you need 2000 ÷ 1000 = 2 ml of concentrate and 2000 − 2 = 1998 ml of water. When the ratio is large, the concentrate is a tiny amount, so you can treat the water as roughly equal to the final volume.
Dilution ratio and concentration are two sides of the same coin. If you treat the concentrate as 100%, 10× is 10%, 100× is 1% and 1000× is 0.1%. For products that state their own concentration, such as bleach or ethanol, you can turn the target into a ratio with "concentrate strength ÷ target strength" (taking 6% bleach down to 0.05% is 120×). Working from concentration is covered in more detail in how to dilute sodium hypochlorite.
The calculation depends on whether you fix the final volume, the water or the concentrate
Dilution calculations come in three flavours, depending on which amount you decide first. If your sprayer or bottle holds a set amount, start from the final volume. If you have already filled a bucket, start from the water. If you want to use up a whole bottle of concentrate, start from the concentrate.
| Amount you fix first | How to find the concentrate | Example (1000×) |
|---|---|---|
| Final volume | Final volume ÷ ratio | Make 2 L → 2 ml concentrate, 1998 ml water |
| Water volume | Water ÷ (ratio − 1) | Add to 2 L of water → about 2.002 ml concentrate (about 2002 ml in total) |
| Concentrate volume | Concentrate × ratio gives the final volume | Use up 5 ml → 5 L in total (4995 ml water) |
With a large ratio like 1000×, the concentrate differs by only about 0.002 ml between starting from the final volume and starting from the water, so it does not matter. The difference becomes visible with small ratios like 10× or 20×. To make 500 ml at 10× you need 50 ml of concentrate and 450 ml of water, but adding concentrate to 500 ml of water at 10× takes 500 ÷ 9 = about 55.6 ml.
"1 part to 10 parts water" is not the same as 10×: two ways of counting
Commercial cleaners, floor waxes and some deodorisers use a ratio such as "1 part concentrate to 10 parts water" or "dilute 1:10". This means adding 10 parts water to 1 part concentrate, so the final mix is 11 times the concentrate. It counts differently from the "×" on pesticide and fertiliser labels, which is based on the total volume.
| Label | Concentrate : water | Concentrate for 500 ml | Water |
|---|---|---|---|
| 10× (total basis) | 1 : 9 | 50 ml | 450 ml |
| 1 part to 10 parts water | 1 : 10 | About 45.5 ml | About 454.5 ml |
| 100× (total basis) | 1 : 99 | 5 ml | 495 ml |
| 1 part to 100 parts water | 1 : 100 | About 4.95 ml | About 495 ml |
The larger the ratio, the smaller the gap between the two: 100× and 1:100 differ by about 1%, and at 1000× they are practically the same. If you are unsure which one a label means, look for a worked example such as "add X ml of concentrate to Y L of water" and work backwards from it. The tool lets you switch between the total basis and 1 part concentrate to N parts water.
Dilution chart (500 ml, 1 L, 2 L)
This chart shows the concentrate needed for common ratios and final volumes, on a total basis. The water is final volume minus concentrate.
| Ratio | 500 ml | 1 L | 2 L |
|---|---|---|---|
| 100× | 5 ml | 10 ml | 20 ml |
| 250× | 2 ml | 4 ml | 8 ml |
| 500× | 1 ml | 2 ml | 4 ml |
| 1000× | 0.5 ml | 1 ml | 2 ml |
| 2000× | 0.25 ml | 0.5 ml | 1 ml |
Amounts for sprayers of 4 L and above, and how many grams of a powdered product to dissolve, are in the pesticide dilution chart. For ratios and volumes not in the table, enter them in the tool and it gives the millilitres of concentrate and water straight away.
Tips for measuring small amounts of concentrate accurately
At 1000× or 2000×, the concentrate comes to about 1 ml or less. Measuring by eye can easily make the mix two or three times too strong, so measure carefully.
- A plastic bottle cap holds about 5 ml, a teaspoon is 5 ml and a tablespoon is 15 ml. You can use these for 5 ml or more
- For 1 to 2 ml, a graduated dropper or a needle-free measuring syringe is accurate
- If you need less than 1 ml, either make a larger batch so the concentrate is easier to measure, or first make a 10× pre-dilution and use ten times as much of that
- Put about half the water in the container first, add the concentrate, then top up with the rest of the water. It mixes better and foams less
- Keep measuring tools separate from the ones you use for food, and wash them well after use
The tool also restates the concentrate as a number of teaspoons, tablespoons or bottle caps. 2 L at 250× needs 8 ml of concentrate (about 1.6 caps), and 2 L at 100× needs 20 ml (4 caps). Check that you can measure it with what you have before you start and you will not go wrong.
FAQ
- Does diluting 1000 times mean 1 ml of concentrate in 1 L of water?
- Strictly speaking, you add 999 ml of water to 1 ml of concentrate to make 1 L in total. With a ratio as large as 1000×, though, 1 ml in 1 L of water differs in strength by only about 0.1%, so in practice you can treat them as the same.
- What is the formula for a dilution ratio?
- Dilution ratio = final volume ÷ concentrate volume. The concentrate is final volume ÷ ratio, and the water is final volume − concentrate. If you fix the water first, the concentrate is water ÷ (ratio − 1).
- What dilution is 1 part concentrate to 10 parts water?
- The final mix is 11 times the concentrate, so on a total basis it is 11×. To make 500 ml you need about 45.5 ml of concentrate and about 454.5 ml of water, slightly weaker than 10× (50 ml of concentrate and 450 ml of water).
- How do I make a 100× dilution?
- Divide the final volume by 100 to get the concentrate. For 500 ml, use 5 ml of concentrate (one bottle cap) and 495 ml of water; for 1 L, 10 ml and 990 ml; for 2 L, 20 ml and 1980 ml.
- What should I do if I need less than 1 ml of concentrate?
- Either make a larger batch so the concentrate is easier to measure, or first dilute the concentrate 10 times and use ten times as much of that (5 ml instead of 0.5 ml). A graduated dropper or syringe makes it even more accurate.
Tools in this article
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