Two-Stroke Fuel Mix Calculator (Petrol and Oil Ratio)
Millilitres of two-stroke oil to add to a given amount of petrol for a 50:1, 40:1 or any other ratio, and the ratio you really have if you already added the oil.
Results
The dashed line marks the value you entered.
What this tool does
A mix ratio of 50:1 means fifty parts of petrol to one of oil, not fifty per cent: 5 litres of petrol takes 100 mL of oil, and a ratio of 25:1 takes 200 mL. Chainsaws, strimmers, outboards and older mopeds each specify their own, usually in the manual or on the fuel cap, and modern synthetic oils are often rated for leaner ratios than mineral ones; too little oil scores the cylinder and too much fouls the plug. Mix in a clean can, shake well, and use the fuel within a few weeks.
Formula
oil (mL) = petrol (L) × 1000 ÷ ratio · 1 US fl oz = 29.5735 mL · ratio actually mixed = petrol (mL) ÷ oil (mL)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
fv | Petrol to mix | L |
rt | Mix ratio, petrol to oil (the 50 in 50:1) | — |
oa | Oil you actually added | mL |
OM | Two-stroke oil to add | mL |
OZ | The same in US fluid ounces | fl oz |
TT | Total mixed fuel | L |
RA | Ratio you actually have (the first number) | :1 |
Worked example
- Petrol to mix5 L
- Mix ratio, petrol to oil (the 50 in 50:1)50
- Oil you actually added100 mL
- Two-stroke oil to add100 mL
- The same in US fluid ounces3.4 fl oz
- Total mixed fuel5.10 L
- Ratio you actually have (the first number)50.0 :1
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.