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Gas / Oil Mix Calculator
Your fuel mix
Always check your engine’s manual for the right ratio — too little oil can seize a 2-stroke engine, and too much oil fouls the spark plug and smokes.
Example: 5 gallons of gas at a 50:1 mix → 12.8 fl oz of oil (378.5 mL).
Behind the numbers
How the gas / oil mix is calculated
A 2-stroke engine has no separate oil sump, so the oil is mixed straight into the gasoline. The ratio tells you how many parts of gas go with one part of oil: at 50:1, every 50 parts of gas need 1 part of oil. Since one US gallon is 128 fluid ounces, the oil in fluid ounces is simply the gallons of gas times 128, divided by the ratio.
For the example: 5 × 128 ÷ 50 = 12.8 fl oz of oil, which is 378.5 mL (1 fl oz = 29.5735 mL). That works out to 2.56 fl oz of oil per gallon of gas.
A few comparisons
Common mixes, worked out
Same idea, different ratios and amounts. Richer mixes (smaller first number) need more oil per gallon.
| Gas | Ratio | Oil needed |
|---|---|---|
| 1 gal | 50:1 | 2.56 fl oz (75.7 mL) |
| 2 gal | 40:1 | 6.4 fl oz (189.3 mL) |
| 2.5 gal | 25:1 | 12.8 fl oz (378.5 mL) |
| 5 gal | 50:1 | 12.8 fl oz (378.5 mL) |
| 5 gal | 32:1 | 20 fl oz (591.5 mL) |
Mix it right, every time.
Mix in a separate fuel can, not in the tank: pour the oil in first, add the gas, then shake the can so the oil blends evenly.
Use the ratio your manual asks for. Most modern 2-stroke tools run 50:1, but older engines and some outboards need 32:1 or 25:1.
Too little oil starves the engine and can seize it; too much oil fouls the spark plug, smokes and wastes fuel. Measure, don’t guess.
Mixed fuel goes stale in about 30 days. Mix only what you will use, and use fresh gas with the right 2-stroke oil — never straight motor oil.
Good to know
Your gas / oil mix questions, answered.
How much oil do I need for 5 gallons of gas at 50:1?
12.8 fluid ounces (378.5 mL). The math is 5 × 128 ÷ 50 = 12.8 fl oz, which is 2.56 fl oz of oil per gallon of gas.
What does 50:1 mean?
It means 50 parts of gasoline to 1 part of oil by volume. For every 50 gallons (or ounces, or liters) of gas, you add 1 of oil. A bigger first number means a leaner mix with less oil.
What happens if I use the wrong ratio?
Too little oil leaves the engine unlubricated and can seize a 2-stroke engine, which is often a costly repair. Too much oil causes smoke, fouled spark plugs and carbon buildup. Always follow your engine manual’s ratio.
Can I use regular motor oil instead of 2-stroke oil?
No. Two-stroke oil is made to burn cleanly with the fuel; regular motor oil does not burn the same way and will leave heavy deposits and smoke. Use oil rated for 2-stroke engines (TC-W3 for outboards, JASO FD or ISO-L-EGD for small tools).