Mixing Ratios Made Easy: Concrete, Epoxy, 2-Stroke Fuel and Cleaning Solutions
"Mix at 50:1." "Dilute 1:10." "Use a 1:2:3 mix." Labels love ratios, but they rarely tell you how many millilitres to actually pour. This guide shows you how to turn any mixing ratio into real quantities, with quick reference tables for the most common jobs.
What a mixing ratio really means
A ratio like 50:1 means 50 parts of one ingredient for every 1 part of another. A "part" can be any unit (a millilitre, a cup, a bucket) as long as you use the same unit for every ingredient.
The key detail people miss: a 50:1 mix contains 51 parts in total. That gives you two slightly different ways to calculate, depending on what you already know.
Method 1: You know the amount of the main ingredient
This is the most common case: you have 5 litres of petrol and want to know how much oil to add. Divide the main ingredient by its share of the ratio:
As a proportion: 50 : 1 = 5000 : x, so x = 100.
Method 2: You know the total amount you want
If you need exactly 1 litre of finished mix, divide the total by the number of parts, then multiply by each ingredient's share:
oil = 1 × 19.6 = 19.6 ml · petrol = 50 × 19.6 = 980.4 ml
For large ratios like 50:1, the two methods give nearly identical answers. For small ratios like 2:1 or 1:1, the difference is big, so pick the right one.
Solve Method 1 instantly. Here the calculator has 50 : 1 = 5000 : ? already filled in.
Open the calculator2-stroke fuel mix (petrol and oil)
Chainsaws, string trimmers, leaf blowers, and many small engines run on a petrol and 2-stroke oil mix. The ratio is petrol : oil, so 50:1 means 50 parts petrol to 1 part oil.
| Ratio | Oil per 1 L petrol | Oil per 5 L petrol | Oil per 1 US gal |
|---|---|---|---|
| 50:1 | 20 ml | 100 ml | 2.6 fl oz |
| 40:1 | 25 ml | 125 ml | 3.2 fl oz |
| 32:1 | 31 ml | 156 ml | 4.0 fl oz |
| 25:1 | 40 ml | 200 ml | 5.1 fl oz |
The US gallon column uses 1 gallon = 128 fl oz. For example, at 50:1 that is 128 ÷ 50 = 2.56 fl oz.
Always use the ratio in your equipment's manual. Running an engine too lean (not enough oil) can seize it. The numbers above are the maths, not a recommendation for your specific machine.
Epoxy resin and two-part adhesives
Epoxy is usually sold as a resin : hardener ratio such as 1:1, 2:1, or 3:1. Here you almost always know the total you need, so use Method 2.
Example: 150 ml of a 2:1 epoxy
Total parts = 2 + 1 = 3. One part = 150 ÷ 3 = 50 ml.
Resin = 2 × 50 = 100 ml. Hardener = 1 × 50 = 50 ml.
Example: Matching what is left in the bottle
You only have 30 ml of hardener left for a 2:1 epoxy. How much resin do you need?
2 : 1 = x : 30, so x = 60 ml of resin.
By volume or by weight? Check the label. Resin and hardener often have different densities, so a 2:1 ratio by volume is not the same as 2:1 by weight. Use cups for volume ratios and a scale for weight ratios, never a mix of both.
Concrete and mortar (three-part ratios)
Concrete recipes are often written as cement : sand : gravel. A commonly used general-purpose mix is 1:2:3. Three-part ratios work exactly like two-part ones: add up the parts, then share out the total.
Example: A 12-bucket batch at 1:2:3
Total parts = 1 + 2 + 3 = 6. One part = 12 ÷ 6 = 2 buckets.
Cement = 2 buckets, sand = 4 buckets, gravel = 6 buckets.
Two practical notes. First, measure every ingredient with the same container, so that "one bucket" always means the same volume. Second, water is added separately and has a big effect on strength. Follow the guidance for your cement or bagged mix rather than guessing.
Cleaning concentrates and dilutions
Dilution ratios are where labels get confusing, because "1:10" is used in two different ways:
- 1 part concentrate to 10 parts water (11 parts in total). This is the strict ratio meaning.
- 1 part in 10 total (1 part concentrate + 9 parts water). Some labels use it this way.
Example: Filling a 500 ml spray bottle at 1:10
1 + 10 interpretation: one part = 500 ÷ 11 = 45.5 ml. Use 45.5 ml concentrate and 454.5 ml water.
1-in-10 interpretation: use 50 ml concentrate and 450 ml water.
The difference is small for a spray bottle, but it adds up for larger batches. If the label shows a table like "1 cup per gallon," trust that over your own interpretation of the ratio.
Safety: never mix bleach with ammonia-based or acidic cleaners. The combination releases toxic gases. Dilute one product at a time, with water only.
Mixing ratio cheat sheet
| You know… | Do this | Example (2:1) |
|---|---|---|
| Amount of ingredient A | B = A × (B part ÷ A part) | 200 ml A → 100 ml B |
| Amount of ingredient B | A = B × (A part ÷ B part) | 40 ml B → 80 ml A |
| Total batch size | One part = total ÷ sum of parts | 300 ml → 200 ml A + 100 ml B |
Using the ratio calculator for mixes
For Method 1, enter the ratio as A and B, then your known amount as C. For example, 50 : 1 = 5000 : ? gives 100.
For Method 2, use a small trick: replace A with the total number of parts. To find the oil in 1000 ml of 50:1 mix, enter 51 : 1 = 1000 : ? and you get 19.6 ml.
Keep the units consistent
Ratios have no units, so you can measure in anything, but every ingredient has to use the same unit. Handy conversions: 1 US gallon = 3.785 L, 1 imperial gallon = 4.546 L, and 1 US fl oz = 29.57 ml.
Frequently asked questions
Is 50:1 the same as 2%?
Roughly. In a 50:1 mix, the oil is 1 out of 51 parts, which is about 1.96% of the total. People often round that to 2%.
Which number comes first in a mixing ratio?
There is no universal rule. Fuel ratios are usually petrol : oil, epoxy is usually resin : hardener, and dilutions are usually concentrate : water. When in doubt, the larger number is almost always the base liquid.
How do I scale a mix up or down?
Multiply or divide every part by the same number. A 1:2:3 concrete mix doubled is 2:4:6, which is still the same ratio, just a bigger batch.
Does a ratio by volume equal a ratio by weight?
Only if the ingredients have the same density, which is rare. Always follow whichever one the manufacturer specifies.