Premix calculator
Pick your ratio, say how much fuel you are mixing, and pour with confidence.
Premix
Pick a ratio, say how much fuel you are mixing, and get the oil amount in both units.
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Measure the oil, then add fuel to it — pouring oil into a part-filled can mixes far better than the other way round.
Ratios here are fuel to oil, the convention used on the bottle and in your manual. Use the ratio your engine builder or manual specifies rather than the one that sounds safest: too much oil leans the mixture out.
Getting it right
Use the ratio your manual or engine builder specifies. Richer is not automatically safer: oil displaces fuel, so more oil leans out the fuel-air mixture, which can run the engine hotter rather than cooler.
Mix in the can, not the tank. Put the oil in first, add a little fuel, swirl, then fill the rest. Fuel poured onto oil sitting in the bottom of an empty can mixes poorly.
Label the can with the ratio and the date. Pump fuel goes off within a few weeks, and mixed fuel goes off faster.
These numbers are arithmetic, not opinion: oil volume is fuel volume divided by the ratio. The only judgement call is which ratio, and that one belongs to your manual.
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