How this calculator works
The ratio tells you how many parts of gasoline go with one part of oil, by volume. To find the oil, divide the volume of the gasoline by the ratio. A US gallon is 128 fluid ounces, so a gallon at 50:1 takes 128 ÷ 50 = 2.56 ounces of oil. To go the other way, divide the volume of gasoline by the volume of oil.
Worked example: 1 US gallon of gas at 50:1 needs 2.56 fl oz (76 mL, 5.1 tablespoons) of two-stroke oil. At 40:1 it is 3.20 oz, at 32:1 4.00 oz and at 25:1 5.12 oz. Five gallons at 50:1 needs 12.8 oz, and 5 liters needs 100 mL. If you added 3.2 oz to a gallon, the mix is 40:1.
Ounces of oil per gallon of gas
US fluid ounces of two-stroke oil to add.
| Gasoline | 16:1 | 25:1 | 32:1 | 40:1 | 50:1 | 100:1 |
|---|---|---|---|---|---|---|
| 0.25 gal | 2.00 | 1.28 | 1.00 | 0.80 | 0.64 | 0.32 |
| 0.5 gal | 4.00 | 2.56 | 2.00 | 1.60 | 1.28 | 0.64 |
| 1 gal | 8.00 | 5.12 | 4.00 | 3.20 | 2.56 | 1.28 |
| 2 gal | 16.00 | 10.24 | 8.00 | 6.40 | 5.12 | 2.56 |
| 2.5 gal | 20.00 | 12.80 | 10.00 | 8.00 | 6.40 | 3.20 |
| 5 gal | 40.00 | 25.60 | 20.00 | 16.00 | 12.80 | 6.40 |
Tips before you buy
- Always use the ratio in the engine manual. Many newer hand-held tools call for 50:1, and some older ones for 32:1 or 40:1.
- A gallon of 50:1 mix needs 2.6 ounces of oil. Most bottles are marked with a measure for gallons or have the right dose for a size of can.
- Pour the oil in first, add half the fuel, shake, then add the rest, so it mixes through.
- Label the can with the date and the ratio. Old mix goes stale in a month or two, and you do not want to put straight gas in a tool that needs the oil.
- Do not use 4-stroke motor oil, which is not made to burn with the fuel.
Tools & materials for this project
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Frequently asked questions
How much oil for 1 gallon of gas at 50:1?
2.56 fluid ounces (76 mL, about 5.1 tablespoons).
How much oil for 1 gallon of gas at 40:1?
3.2 fluid ounces (95 mL). At 32:1 it is 4 ounces, and at 25:1 5.12 ounces.
How much oil for 5 gallons of gas at 50:1?
12.8 fluid ounces (379 mL).
How much oil for 5 liters of gas at 50:1?
100 mL, which is 1 part in 50: 20 mL per liter.
What is the ratio if I added 3.2 ounces to a gallon?
40:1, because a gallon is 128 ounces and 128 ÷ 3.2 is 40.
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