2 Stroke / 2 Cycle Gas Oil Fuel Mix Ratio Calculator

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.

Common ratios
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Oil per litre, compared

What a two stroke oil ratio actually means

A ratio written as 50:1 means fifty parts petrol to one part oil, measured by volume. It is not fifty percent of anything, and the “1” is the oil. So one litre of petrol takes 1000 ÷ 50 = 20 ml of two stroke oil, and the oil ends up as 1.96% of the finished mix.

Fifty units of petrol shown beside one unit of oil 50 PARTS PETROL 1 PART TWO STROKE OIL
Each block is the same volume. Fill fifty of them with petrol, one with oil, and that is a 50:1 mix.

Because the oil scales with the fuel, the figure per litre never changes: 20 ml at 50:1 whether you are mixing one litre or twenty. That is what makes the oil per litre column in the chart below the number worth memorising.

Ratio, percentage and oil per litre

People describe the same mix three different ways, which causes a lot of confusion at the pump. These are all identical:

  • 50:1 — the ratio, fuel first
  • 2% — near enough the oil’s share of the mix (1.96% exactly)
  • 20 ml per litre — the dose

Gas and oil mix chart

Every common two stroke ratio, with the oil worked out for a litre, a US gallon and a UK gallon. The highlighted rows are the four you will meet most often. Use it as a printable gas and oil mix chart for the shed wall, or let the fuel mix calculator above do an odd quantity for you.

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 fluid ounces for UK gallons — the two are not the same size, which is why a US gallon takes fewer ounces of oil than a UK one at the same ratio.

The ratios people search for most

50 to 1 gas oil mix

The default for almost all modern garden machinery and a great many outboards. 20 ml of oil per litre, or 2.56 US fl oz per US gallon. For a 5 litre can that is 100 ml of oil; for a 2 gallon US can, a shade over 5 fl oz.

40 to 1 gas oil mix

Common on 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.

32:1 fuel mix

Typical premix for two stroke dirt bikes and older saws. 31.3 ml per litre, or exactly 4 US fl oz per US gallon, which is the reason it stuck around — it is a neat half-cup.

25:1 oil petrol mix

Pre-1980s outboards and a lot of older equipment. 40 ml per litre or 5.12 US fl oz per US gallon.

10:1 mixing ratio

Far richer than any modern engine wants — 100 ml per litre, 9.09% oil. You will meet it on running-in schedules for some vintage engines and in non-fuel mixing jobs, but never assume it for a two stroke without checking.

How to mix two stroke fuel properly

  1. Work out the oil with the calculator above, and use a measuring jug or the graduated bottle the oil came in. Eyeballing it is where most mixes go wrong.
  2. Use a clean, sealed fuel can meant for gasoline. Never mix in the machine’s own tank — you cannot shake it properly and the oil will sit at the bottom.
  3. Pour in roughly half the petrol first, then all of the oil, then the rest of the petrol. Adding oil to a part-full can helps it disperse instead of clinging to the bottom.
  4. Cap it and shake for a good thirty seconds. A correctly mixed batch looks evenly tinted throughout, with no streaks when you tilt the can.
  5. Label the can with the ratio and the date. Two cans of different mix that look identical is a genuinely expensive mistake.
  6. Use it within about a month. Gasoline goes stale, and the ethanol in pump fuel can separate out, which leaves the oil behind and the engine running dry.

Mistakes that cost engines

Mixing the ratio upside down. 50:1 is fifty of petrol to one of oil. Reading it the other way gives you a can of oil with a splash of petrol in it.

Confusing US and UK gallons. A UK gallon is about 20% larger. Dosing a UK gallon with the US figure leaves the mix noticeably lean.

Using car engine oil. Four stroke oil is not designed to burn. It leaves deposits on the piston crown, the ring grooves and the exhaust port. Use oil marked TC, JASO FB/FC/FD or API TC, and match your machine’s requirement.

Adding oil to a two stroke that injects its own. Many scooters and outboards have an oil pump and take neat petrol in the tank. Premixing on top of that fouls plugs fast.

Running last season’s can. Stale mix is a leading cause of hard starting after a winter in the shed. Drain it and mix fresh.

Two stroke fuel mixing FAQs

How much oil do I put in 1 litre of petrol?

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 and you have the answer in millilitres.

How much 2 stroke oil per gallon at 50:1?

2.56 US fluid ounces per US gallon, or 3.2 imperial fluid ounces per UK gallon. In metric that is about 75.7 ml for a US gallon and 90.9 ml for a UK one.

Is 2 stroke oil the same as 2 cycle oil?

Yes. “Two stroke” is the British term and “two cycle” the American one for the same engine and the same oil. Any chart labelled 2-cycle applies unchanged to a two stroke.

The same goes for the tools. Spelled out, a two stroke oil calculator, a two cycle oil calculator and a two stroke oil ratio calculator are one thing; abbreviated, so are a 2 stroke oil mix calculator, a 2 cycle oil mix calculator and a 2 cycle oil ratio calculator. A gas oil ratio calculator, an oil to gas mix calculator, a premix oil calculator and a petrol mix calculator all land on the same sum. Only the vocabulary changes with the country.

What happens if I put too much oil in a two stroke?

It runs rich and smoky, fouls spark plugs, coats the exhaust port and silencer in carbon and loses power. It rarely destroys an engine on its own, but a summer of it will leave you decoking the exhaust.

What if there is not enough oil in the mix?

Far more serious. A lean mix starves the big end and the piston skirt of lubrication, and the usual result is a scored bore or a seizure. If you are unsure whether a can is right, err on the oily side and mix fresh.

Can I use 40:1 instead of 50:1?

Running 40:1 in an engine specified for 50:1 adds a little oil and is generally tolerated, at the cost of more smoke and carbon. Going the other way — 50:1 in an engine that asks for 40:1 or 32:1 — removes lubrication the designer intended, and is the riskier substitution.

How long does mixed two stroke fuel last?

About a month in a sealed can, less in heat or if the can is half empty. Ethanol-blended pump petrol absorbs water and can separate. A fuel stabiliser extends that to a few months, but fresh is always better.

What is the difference between premix and oil injection?

Premix means you mix oil into the fuel can yourself. Oil injection, also called autolube, carries oil in a separate tank and meters it in as the engine runs, so the fuel tank gets neat petrol. Check which one you have before you mix anything.