How to use the two-stroke fuel mix calculator
- Choose Oil to add or The mix ratio.
- To find the oil, enter the fuel to oil ratio, such as 50 for 50:1, and the fuel amount with its unit.
- To find the ratio, enter the fuel amount and the oil amount you added, in fluid ounces or milliliters.
- Read the oil in milliliters and fluid ounces, tablespoons and teaspoons, and the total mix.
Formula
oil = fuel / X for a ratio of X parts fuel to 1 part oil
ratio X = fuel / oil
total mix = fuel + oil
1 US gallon = 3,785.41 mL; 1 US fluid ounce = 29.5735 mL
The ratio counts parts of fuel to one part of oil, so oil is 1 / (X + 1) of the finished mix. A tablespoon is half a US fluid ounce and a teaspoon is one sixth.
Fifty to one in a gallon
One US gallon of fuel is 3,785.4 mL. At 50:1 the oil is 3,785.4 / 50 = 75.7 mL, which is 2.56 US fluid ounces, 5.12 tablespoons or 15.4 teaspoons. The finished mix is 3,861.1 mL, and oil is 1.961 percent of it.
At 40:1 in 5 liters of fuel, the oil is 125 mL, 4.23 fluid ounces. Working the other way, 2.6 fluid ounces added to one US gallon gives a ratio of 49.23:1, so the mix is a little richer than 50:1.
Why the ratio matters
In a two-stroke engine the oil is mixed into the fuel and burned to lubricate the engine. Too little oil can cause wear and damage, and too much can foul spark plugs and make smoke. Equipment makers state the ratio and often the type of oil to use. Follow your manual, and do not rely on a number from another machine.
Ratios are written as fuel to oil, so a lower first number means more oil. A 40:1 mix has more oil than 50:1. Some labels list ounces of oil for a gallon, which is the same idea in other units.
Mixing safely
Measure with a marked container, mix in an approved fuel container, and do it away from heat, sparks and flame. Shake the container so the oil blends in, and label it with the ratio and the date. Fuel with oil in it can go stale, so mix only what you will use soon. For a different kind of mixing, see the Alligation Mixture Calculator. For the cost of fuel, use the Fuel Cost Calculator, and for stove fuel on a trip, the Camp Stove Fuel Calculator.
Assumptions and limits
- The ratio is parts of fuel to one part of oil, with the oil added to the fuel amount.
- US gallons, US quarts, liters and imperial gallons use their standard sizes.
- Fluid ounces are US fluid ounces.
- The ratio shown when the page opens is an example and not the ratio for your engine.
Frequently asked questions
Does 50:1 mean 50 parts fuel in total or 50 parts plus one of oil?
It means 50 parts of fuel plus 1 part of oil. The finished mix is 51 parts, so oil makes up 1 / 51, about 1.96 percent.
How many ounces of oil for a gallon at 40:1?
One US gallon is 128 fluid ounces, so at 40:1 the oil is 128 / 40 = 3.2 US fluid ounces. The page shows this and other combinations in the units you choose.
Why is a tablespoon of oil shown?
Small amounts of oil are often measured with kitchen spoons. The page gives tablespoons and teaspoons, though a marked oil bottle or a measuring cup is more accurate.
Can I mix a small amount?
Yes. Enter the small fuel amount, such as a quart, and the page scales the oil to match. For very small amounts, use milliliters and a syringe or marked bottle.