2-Stroke Oil Mix Calculator

How it works

oil = fuel ÷ ratio · mL of oil = litres × 1,000 ÷ ratio · fl oz of oil = gallons × 128 ÷ ratio · oil % = 100 ÷ ratio

Two-stroke engines are lubricated by oil premixed into the fuel, and the ratio on the engine or in the manual — 50:1 for most modern chainsaws and trimmers, 40:1 or 32:1 for older tools and dirt bikes, 100:1 for some outboards with specific oils — means that many parts of gasoline to one part of oil. Too little oil scores the piston; too much fouls plugs and smokes. Because the ratio is by volume, the amount of oil is simply the fuel volume divided by the ratio: 20 mL per litre at 50:1, or 2.6 fl oz per US gallon. Mix in a clean can, oil first and then fuel, and shake before each use.

Worked example

5 L of gasoline at 50:1 needs 5,000 ÷ 50 = 100 mL of 2-stroke oil (2.00% of the mix), giving 5.10 L of premix. At 1 US gallon and 50:1 you would add 2.6 fl oz.

Sources: JASO M345 two-stroke oil standard (JALOS) · U.S. EPA — Small equipment and tools

Frequently asked questions