2-Stroke Fuel Mix Calculator
Enter how much fuel you're mixing and the ratio your engine needs to get exactly how much two-stroke oil to add — no guesswork, no seized engines.
Two-stroke engines — chainsaws, trimmers, leaf blowers, outboards, dirt bikes — burn a mix of petrol and oil. Get the ratio wrong and you either starve the engine of lubrication (too little oil) or foul the plug and smoke (too much). This calculator turns your fuel quantity and the ratio into an exact oil measurement.
How to mix 2-stroke fuel
A ratio like 50:1 means 50 parts fuel to 1 part oil. Since a US gallon is 128 fluid ounces, divide 128 by the ratio to get the ounces of oil per gallon; in metric, a litre is 1,000 ml, so divide 1,000 by the ratio for millilitres of oil per litre.
Oil (ml) = Fuel (litres) × 1000 ÷ Ratio
| Ratio | Oil per US gallon | Oil per litre |
|---|---|---|
| 100 : 1 | 1.3 oz | 10 ml |
| 50 : 1 | 2.6 oz | 20 ml |
| 40 : 1 | 3.2 oz | 25 ml |
| 32 : 1 | 4.0 oz | 31 ml |
| 25 : 1 | 5.1 oz | 40 ml |
| 16 : 1 | 8.0 oz | 63 ml |
Worked example
Mixing 2.5 gallons of fuel at 40:1:
| Total fluid ounces = 2.5 × 128 | 320 oz |
| Oil = 320 ÷ 40 | 8.0 oz |
Tips for a clean mix
Always use the ratio in your equipment's manual — it overrides any rule of thumb. Use fresh fuel and a quality two-stroke oil, mix in an approved container (add oil first, then fuel, and shake), and don't store mixed fuel for more than about a month, since it degrades and can harm the engine. When in doubt between two ratios, a touch more oil is safer than too little.