Mixing Ratio Calculator
Enter the ratio of two components (A to B) and the total amount you want to make. The calculator shows the exact amount of each component and the percentage each one contributes. Switch modes to reverse-solve the ratio from known component amounts, or to calculate the meteorological mixing ratio for atmospheric humidity.
What is a mixing ratio?
A mixing ratio describes the proportion of two (or more) substances in a mixture. It is written as A:B, meaning for every A units of the first component you add B units of the second. A 1:4 ratio means one part A to four parts B, giving a total of five parts. The ratio tells you nothing about the size of a "part" - a part can be a millilitre, a litre, a gram, or a gallon, but all measurements must be in the same unit throughout a single mix. Ratios are used in chemistry, manufacturing, painting, cooking, adhesives, engine fuels, and dozens of other fields where exact proportions determine whether a product performs correctly.
How to calculate component amounts from a ratio
To find the amount of each component, first add all the ratio parts together to get the total number of parts. Then divide each individual part by that sum to find its fraction, and multiply the fraction by your desired total quantity. For a 1:4 ratio giving a 500 mL total: there are 1 + 4 = 5 parts. Component A is (1/5) x 500 = 100 mL, and component B is (4/5) x 500 = 400 mL. You can scale the formula up or down freely: the ratio stays constant while only the total changes.
Reverse-solving: finding the ratio from known amounts
If you already have two components measured out and want to know the ratio, divide each amount by the other to express the relationship, then simplify. For example, 200 mL of A and 800 mL of B: total = 1000 mL. A is 20 % of the mix (200/1000) and B is 80 % (800/1000). The ratio in simplest form is 1:4 (dividing both by 200). Percentage composition is a useful alternative expression: it immediately shows each component as a share of the whole. The calculator uses the greatest common divisor (GCD) to automatically reduce any ratio to its lowest whole-number form.
Meteorological mixing ratio
In atmospheric science the term "mixing ratio" has a specific meaning: the mass of water vapour present per unit mass of dry air, expressed in grams per kilogram (g/kg). It is calculated as w = 0.622 x e / (p - e), where e is the actual vapour pressure and p is the total atmospheric pressure, both in the same units (kPa in this calculator). The constant 0.622 is the ratio of the molar mass of water (18 g/mol) to that of dry air (29 g/mol). Unlike relative humidity, the mixing ratio does not change as air warms or cools without adding or removing moisture, making it a conservative quantity used to trace air masses across weather systems. Typical values range from about 1 g/kg in cold dry polar air to 20 g/kg or more in hot humid tropical air.
Common mixing ratios by application
| Application | Typical ratio (A:B) | A % | B % | Notes |
|---|---|---|---|---|
| Two-part epoxy resin | 1:1 | 50 % | 50 % | Resin to hardener |
| Epoxy (structural) | 2:1 | 66.7 % | 33.3 % | Resin to hardener by volume |
| Polyester body filler | 50:1 | 98 % | 2 % | Filler to catalyst |
| Diluted bleach (cleaning) | 1:9 | 10 % | 90 % | Bleach to water |
| Hydrogen peroxide disinfectant | 1:4 | 20 % | 80 % | H2O2 to water |
| Car coolant (standard) | 1:1 | 50 % | 50 % | Coolant to water |
| Car coolant (winter) | 3:2 | 60 % | 40 % | Coolant to water |
| Fuel mix (2-stroke engine) | 1:50 | 2 % | 98 % | Oil to petrol |
| Concrete (basic) | 1:2 | 33.3 % | 66.7 % | Cement to sand/aggregate |
| Hair developer (tint) | 1:2 | 33.3 % | 66.7 % | Colour to developer |
Typical A:B ratios used across industries. Always verify with the product manufacturer.
Frequently asked questions
What does a 1:10 mixing ratio mean?
A 1:10 ratio means one part of component A for every ten parts of component B. The total is 11 parts, so A is 1/11 (about 9.1 %) and B is 10/11 (about 90.9 %) of the finished mixture. To make 1 litre you would use roughly 91 mL of A and 909 mL of B.
Does it matter whether I mix by volume or by weight?
Yes, it matters a great deal. Manufacturers specify ratios either by volume or by weight (mass). Unless the two components have the same density, a 1:1 ratio by volume is not the same as 1:1 by weight. Always check the product data sheet and measure in the units specified. Using volume when mass is required (or vice versa) is one of the most common causes of epoxy resin or adhesive failures.
How do I scale a recipe up while keeping the same ratio?
The ratio stays fixed: only the total quantity changes. If a 1:4 ratio at 500 mL needs 100 mL of A and 400 mL of B, then the same ratio at 2 litres needs 400 mL of A and 1600 mL of B. You can use the Multiply by feature: enter the original total, then change it to the new total and the component amounts recalculate automatically.
How is the simplified ratio calculated?
The calculator finds the greatest common divisor (GCD) of the two parts and divides both by it. For example, parts 200 and 800 share a GCD of 200, so the simplified ratio is 1:4. For non-integer inputs the calculation is done on the values multiplied by a scaling factor before applying GCD, to handle decimals like 1.5:2.5, which simplifies to 3:5.
What is the difference between mixing ratio and relative humidity?
Relative humidity compares the actual water vapour content to the maximum possible at the current temperature, expressed as a percentage. It changes as temperature changes even if no moisture is added or removed. The meteorological mixing ratio (g/kg) measures the actual mass of vapour per kilogram of dry air and does not change with temperature, making it more useful for tracking air masses over time.
Can I mix three or more components with this calculator?
This calculator is designed for two-component (A:B) systems, which cover the vast majority of practical applications such as epoxy, hair colour, dilutions, and fuel mixes. For three or more components, apply the same logic iteratively: calculate the total parts, find each fraction, and multiply by the total quantity. The percentage formula (component / total x 100) works for any number of constituents.