2-stroke fuel mix calculator
This splits the fuel you type by the ratio you type — nothing more. The correct ratio is the one stamped on your engine, not a figure this page picks for you. Mix fresh, shake the can, and when in doubt read the manual before you pull the cord.
Enter how much petrol you are mixing and the ratio the engine wants, and the tool returns the volume of two-stroke oil to add — in fluid ounces and millilitres at once — plus the rough total once the oil is in.
Worked example
You are filling a 1-gallon jug at 50:1. A US gallon is 128 fluid ounces, so the oil is 128 ÷ 50 = 2.56 fl oz, which is about 76 mL. Drop to 40:1 and it climbs to 3.2 fl oz (95 mL); the smaller the ratio number, the more oil goes in.
The formula
oil = fuel volume ÷ ratio
The ratio is simply how many parts of petrol share one part of oil, so dividing the fuel by it gives the oil directly in the same units. Convert once to a common unit (millilitres here) and the ounce and millilitre figures fall straight out of it.
Questions
- How much oil goes in a 50:1 mix?
- A 50:1 ratio means 50 parts petrol to 1 part oil, so you divide the fuel by 50. One US gallon at 50:1 is 128 ÷ 50 ≈ 2.6 fluid ounces of oil; one litre is 1000 ÷ 50 = 20 millilitres. Type your ratio and your fuel amount and the tool gives you the oil in both ounces and millilitres.
- What ratio should I mix at?
- Whatever the engine plate or the manual says — it is set by the machine, not by the fuel, so the ratio is a field you fill in rather than a number this tool assumes. Older saws and trimmers often run 32:1 or 40:1; many newer ones are 50:1. When the two disagree, follow the engine.
- Does the ratio number mean petrol-to-oil or oil-to-petrol?
- Petrol to oil. 50:1 is 50 measures of gas for every 1 of oil — a lot of fuel, a little oil. Enter the larger number (the 50) in the ratio field here. Getting it upside down floods the engine with oil, so read it as "fifty of gas, one of oil".
- Can I mix a big batch and keep it?
- Mixed two-stroke fuel goes stale — the petrol oxidises and the additives drop out, often within a month or two. Mix what you will burn in a few weeks, shake the can before each fill, and use a fuel stabiliser if it will sit. This tool sizes the batch; it does not judge how old the can is.
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