STIHL Fuel Mix Ratio Calculator
Work out exactly how much 2-stroke oil to add to your petrol for your STIHL chainsaw, trimmer, or blower — just enter your fuel amount and mix ratio.
Fuel & Ratio Details
Enter your fuel amount and mix ratio to work out how much 2-stroke oil to add
Choose the unit you’re measuring your petrol in.
How much petrol you’re mixing, in the unit selected above.
Select your unit’s specified ratio, or choose Custom to enter your own.
The “X” in an X:1 ratio (e.g. enter 50 for a 50:1 mix). Check your unit’s manual or fuel cap.
Fuel Mix Results
Exact oil and petrol amounts for your mix
Enter your fuel amount and mix ratio above, then click Calculate Fuel Mix to see exactly how much oil to add.
Common STIHL Mix Ratios
Handy reference figures for the most common STIHL 2-stroke mix ratios, so you can double-check your calculation at a glance.
| Ratio | Oil per US Gallon | Oil per Litre |
|---|---|---|
| 50:1 (STIHL HP / HP Ultra) | 2.6 fl oz | 20 ml |
| 40:1 | 3.2 fl oz | 25 ml |
| 32:1 | 4.0 fl oz | 31 ml |
| 25:1 | 5.1 fl oz | 40 ml |
| 20:1 | 6.4 fl oz | 50 ml |
STIHL Fuel Mix FAQ
Answers to common questions about STIHL 2-stroke fuel mixing, ratios, and fuel storage.
Most modern STIHL 2-stroke engines are designed for a 50:1 petrol-to-oil ratio when used with STIHL HP or HP Ultra 2-stroke oil. Always check the ratio printed on your unit’s fuel cap and owner’s manual, since some older models or oil types call for a different ratio.
At a 50:1 ratio, 1 US gallon (128 fluid ounces) of petrol needs 2.6 fluid ounces of 2-stroke oil. This calculator works out the exact figure for any fuel amount and ratio you enter.
At a 50:1 ratio, 1 litre of petrol needs 20 millilitres of 2-stroke oil. At 40:1, it needs 25 millilitres per litre. Always confirm the ratio specified for your particular STIHL model.
Too little oil can cause inadequate lubrication, leading to engine overheating and premature wear or seizure. Too much oil can cause excess smoke, spark plug fouling, carbon build-up, and reduced performance. Mixing accurately protects the engine and keeps warranty cover valid.
Pre-mixed 2-stroke fuel typically starts to degrade after about 30 to 60 days as the petrol oxidises, which can cause starting problems and gum deposits. STIHL recommends mixing only as much fuel as you’ll use within a month, or using a fuel stabiliser for longer storage.