⛽ Two-Stroke Fuel Mix Calculator
For a two-stroke mix, oil = fuel ÷ the ratio number — so 5 litres of petrol at 50:1 needs 5000 ÷ 50 = 100 ml of oil.
100 ml
Two-stroke oil to add
3.4 fl oz
Same amount in fluid ounces
Add this much two-stroke oil to your petrol, then mix well before filling. The ratio is parts fuel to one part oil — a 50:1 mix is 50 parts petrol to 1 part oil, so oil = fuel ÷ 50. Always use the ratio your engine's manufacturer specifies (common for chainsaws, trimmers, outboards and dirt bikes), and a quality two-stroke oil. 🔒 In your browser.
How the two-stroke fuel mix calculator works
A two-stroke (two-cycle) engine burns oil mixed into its petrol for lubrication. The mix ratio is written as fuel:oil — 50:1 means 50 parts petrol to 1 part oil. So the oil you add is simply the fuel volume divided by the ratio number: convert your fuel to millilitres, divide by the ratio, and that's the oil in millilitres (also shown in fluid ounces). Enter litres or US gallons and pick the ratio your equipment specifies.
Always use the exact ratio in your equipment's manual — chainsaws, string trimmers, leaf blowers, outboards and dirt bikes vary (commonly 50:1, 40:1 or 32:1), and older or air-cooled engines often need more oil (richer, lower ratio number). Use a quality two-stroke oil, measure the oil accurately, and shake the container to mix before filling. Too little oil risks seizing the engine; too much fouls the plug and smokes.
Frequently asked questions
How much oil do I put in a 50:1 mix?
Divide the fuel volume by 50. For 1 litre of petrol that's 20 ml of oil; for 1 US gallon it's about 2.6 fl oz. The calculator does it for any fuel amount and ratio.
What does a ratio like 40:1 mean?
It's parts of fuel to parts of oil — 40:1 is 40 parts petrol to 1 part two-stroke oil. A smaller second-number ratio (like 32:1) means more oil per litre than 50:1.
What ratio should I use?
Whatever your engine's manufacturer specifies — it's in the manual and often on the cap or housing. Don't guess: too little oil can destroy the engine. When a range is given, the richer (more oil) end suits heavy or hot running.
Does the oil brand matter?
Use an oil rated for two-stroke/two-cycle engines (often labelled TC-W3 for marine or JASO FD for air-cooled). Mixing to the right ratio with a poor oil still risks damage.