About the Two-Stroke Oil Mix Calculator
This two-stroke oil mix calculator tells you how much oil to add to your gasoline for any fuel-to-oil ratio. Enter how much fuel you are mixing — in US gallons, liters or imperial gallons — choose the ratio printed on your engine or in the owner’s manual, and it returns the oil in US fluid ounces and millilitres, plus the total volume of the finished mix.
It is for chainsaws, string trimmers, leaf blowers, dirt bikes, outboard motors, mopeds and any other engine that burns premix. Getting the ratio right matters: too little oil can score the piston and seize the engine, while too much causes smoke, fouled plugs and carbon build-up.
A 50:1 ratio means 50 parts fuel to 1 part oil by volume, so the oil amount is simply the fuel volume divided by the ratio. Always follow the engine maker’s recommended ratio and use oil rated for two-stroke engines (air-cooled or TC-W3 for water-cooled outboards).
How to use the two-stroke oil mix calculator
- 1Enter how much gasoline you are mixing and pick the unit.
- 2Choose the fuel-to-oil ratio your engine requires, or enter a custom ratio.
- 3Read the oil amount in fluid ounces or millilitres.
- 4Pour the oil into a clean fuel can, add the gasoline and shake to mix.
Formula and method
A fuel-to-oil ratio of R:1 means R parts gasoline to one part oil by volume, so the oil required is the fuel volume divided by R. The fuel is first converted to millilitres (1 US gallon = 3,785.411784 mL, 1 imperial gallon = 4,546.09 mL), divided by the ratio and then converted to US fluid ounces (29.5735 mL) and imperial fluid ounces (28.4131 mL).
Because the oil is added to the gasoline, the finished mix is slightly larger than the fuel alone, and oil makes up 1 ÷ (R + 1) of it — 1.96% at 50:1. The ratio is based on the fuel you start with, which is how engine manufacturers and oil bottles state it.
- Fuel
- Volume of gasoline being mixed
- Ratio (R)
- Parts fuel per one part oil, e.g. 50 for 50:1
- Oil
- Volume of two-stroke oil to add
Worked examples
1 US gallon at 50:1
One US gallon is 128 fl oz, and 128 ÷ 50 = 2.56 fl oz, or about 75.7 mL of oil. Oil is 1 ÷ 51 = 1.96% of the finished mix.
5 liters at 40:1 for a chainsaw
5,000 mL ÷ 40 = 125 mL of oil (about 4.23 US fl oz), giving 5.125 liters of mix.
2.5 US gallons at 32:1 for a dirt bike
2.5 gallons is 320 fl oz; 320 ÷ 32 = 10 fl oz, or about 296 mL of oil.
Frequently asked questions
How much oil do I add to 1 gallon of gas for 50:1?+
Add 2.6 US fluid ounces (2.56 exactly), or about 76 mL. For 40:1 add 3.2 fl oz, for 32:1 add 4 fl oz, and for 25:1 add 5.1 fl oz per US gallon.
What happens if I use the wrong mix ratio?+
Too little oil risks overheating, scored cylinders and engine seizure. Too much oil causes heavy smoke, spark plug fouling, carbon deposits and lower power. A small deviation is usually tolerated, but stick to the manufacturer’s ratio.
Is 50:1 or 40:1 more oil?+
40:1 contains more oil. The smaller the first number, the richer the mix: 32:1 has more oil than 40:1, which has more than 50:1.
How long does mixed 2-stroke fuel last?+
Premix gasoline is best used within about 30 days, as fuel degrades and can leave gum in carburetors. A fuel stabilizer or ethanol-free fuel helps it last longer in seasonal equipment.
Can I use regular motor oil in a 2-stroke engine?+
No. Four-stroke motor oil does not burn cleanly when mixed with fuel and lacks the additives two-strokes need. Use oil labeled for two-cycle engines (JASO FD/ISO-L-EGD for small engines, TC-W3 for water-cooled outboards).