Enter how much gas or gasoline or petrol you are mixing, pick a ratio, and get the exact oil in millilitres or fluid ounces. It runs backwards too, from a part-used bottle of oil to the fuel it will treat.
Garden and outdoor power
Bikes and karts
Marine
50:1 means fifty parts petrol to one part oil, by volume. It is not fifty percent of anything, and the “1” is the oil. One litre of petrol takes 1000 ÷ 50 = 20 ml, which works out as 1.96% of the finished mix.
Because the oil scales with the fuel, the figure per litre never changes — 20 ml at 50:1 whether you mix one litre or twenty. People describe the same mix three ways: 50:1, 2% and 20 ml per litre are all identical.
Every common ratio, worked out for a litre, a US gallon and a UK gallon. The highlighted rows are the four you will meet most often.
| Ratio | Oil per litre | Oil per US gal | Oil per UK gal | Oil % |
|---|---|---|---|---|
| 10:1 | 100 ml | 12.8 fl oz | 16 fl oz | 9.09% |
| 16:1 | 62.5 ml | 8 fl oz | 10 fl oz | 5.88% |
| 20:1 | 50 ml | 6.4 fl oz | 8 fl oz | 4.76% |
| 24:1 | 41.7 ml | 5.33 fl oz | 6.67 fl oz | 4% |
| 25:1 | 40 ml | 5.12 fl oz | 6.4 fl oz | 3.85% |
| 32:1 | 31.3 ml | 4 fl oz | 5 fl oz | 3.03% |
| 40:1 | 25 ml | 3.2 fl oz | 4 fl oz | 2.44% |
| 50:1 | 20 ml | 2.56 fl oz | 3.2 fl oz | 1.96% |
| 60:1 | 16.7 ml | 2.13 fl oz | 2.67 fl oz | 1.64% |
| 80:1 | 12.5 ml | 1.6 fl oz | 2 fl oz | 1.23% |
| 100:1 | 10 ml | 1.28 fl oz | 1.6 fl oz | 0.99% |
US fluid ounces for US gallons, imperial for UK — the two are not the same size, which is why a US gallon takes fewer ounces at the same ratio.
The default for almost all modern garden machinery and many outboards. 20 ml per litre, or 2.56 US fl oz per US gallon. A 5 litre can takes 100 ml.
Older garden two strokes and some trimmers. 25 ml per litre or 3.2 US fl oz per US gallon — a quarter more oil than 50:1.
Typical premix for two stroke dirt bikes and older saws. 31.3 ml per litre, or exactly 4 US fl oz per US gallon — a neat half-cup, which is why it stuck.
Pre-1980s outboards and a lot of older equipment. 40 ml per litre or 5.12 US fl oz per US gallon. Richer still — 10:1, at 100 ml per litre — turns up on vintage running-in schedules, but never assume it.
Three things that cost engines: mixing the ratio upside down; using car engine oil, which is not designed to burn and coats the piston and exhaust port; and premixing for a machine that already injects its own oil.
At 50:1 it is 20 ml. At 40:1, 25 ml. At 32:1, 31.3 ml, and at 25:1, 40 ml. Divide 1000 by the first number of the ratio.
2.56 US fluid ounces per US gallon, or 3.2 imperial fluid ounces per UK gallon — about 75.7 ml and 90.9 ml respectively.
Yes. “Two stroke” is the British term, “two cycle” the American one, for the same engine and the same oil. A 2 stroke oil mix calculator, a 2 cycle oil ratio calculator, a gas oil ratio calculator and a petrol mix calculator all land on the same sum — only the vocabulary changes.
Too much runs rich and smoky, fouls plugs and cokes the exhaust, but rarely destroys an engine. Too little is far more serious — it starves the big end and piston skirt, and the usual result is a scored bore or a seizure. If unsure, err oily and mix fresh.
About a month in a sealed can, less in heat or a half-empty can. Ethanol-blended petrol absorbs water and can separate. A stabiliser extends that to a few months, but fresh is always better.
Premix means you mix oil into the can yourself. Oil injection, or autolube, carries oil in a separate tank and meters it in as the engine runs, so the fuel tank gets neat petrol. Check which you have before mixing anything.
A simplified, open-source version of this tool is on GitHub — the fuel and oil mixing maths as readable, dependency-free code, with tests and a walk-through of how the sums work. Free to read, fork or build on. View the source on GitHub →