Two-stroke mix calculator

Enter the fuel volume and the ratio specified by the equipment manufacturer to calculate the oil amount.

Formulaoil volume = fuel volume ÷ ratio

The ratio is fuel divided by oil

A 50:1 mixture contains one volume unit of oil for every 50 equal volume units of fuel. The result is shown in milliliters and US fluid ounces.

The manufacturer chooses the ratio

Use only the fuel, oil type and ratio specified for your equipment. This calculator cannot determine the correct ratio or verify an existing mixture.

The measures you will actually pour

At 50:1, five litres of petrol takes 100 ml of oil and one US gallon takes 2.56 fl oz. At 40:1 the same five litres takes 125 ml, and at 32:1 a gallon takes exactly 4 fl oz. Those three ratios cover most handheld equipment sold in the last forty years.

Mix in the can, never in the machine. Pour the oil in first, add half the petrol, cap it and shake, then top up and shake again. Oil poured on top of a full can tends to sit there, and the first tankful comes out far richer than the ratio you calculated.

Frequently asked questions

What happens if the mixture is wrong?

Too little oil is the expensive mistake: the piston and bore lose their lubrication and can seize, sometimes within a single tank. Too much oil is merely unpleasant, giving smoke, oily plugs, carbon build-up and a machine that runs poorly. If you are unsure which way you erred, drain it and mix a fresh batch rather than running the tank down.

Can I use ordinary engine oil?

No. Two-stroke oil is designed to burn with the fuel, and four-stroke motor oil is not: it leaves deposits that foul the plug and the exhaust port. Buy oil sold for two-stroke air-cooled engines and matching the specification in your manual, commonly a JASO FD or ISO-L-EGD grade. Marine TC-W3 oil is formulated for water-cooled outboards and is not a substitute.

How long does mixed fuel keep?

Around 30 days in a sealed can is the usual advice, and less in hot weather or a part-empty container. Petrol with ethanol in it absorbs moisture and can separate, which is why equipment that sits between seasons is the most common victim. Mix what you will use, add a stabiliser if it must sit, and run the machine dry before storage.

Does the ratio change with ethanol-blended petrol?

No, the ratio is the same. What changes is what you should buy: most manufacturers accept up to E10 and warn against E15 or higher, because the extra ethanol attacks fuel lines and diaphragms in equipment never designed for it. Some sell pre-mixed ethanol-free fuel for exactly this reason.

My manual says 50:1 but the oil bottle says 40:1. Which wins?

The machine’s manual. The bottle is printing a general recommendation for a range of equipment, while the manufacturer specified a ratio for your engine, its bearings and its cooling. Where the two genuinely conflict, the safer reading is the one with more oil, but check the manual for your model before assuming.