Two-stroke fuel mix calculator
How much two-stroke oil to add to petrol for a chain saw, trimmer, blower or other two-stroke engine.
How it works
Oil = fuel ÷ ratio. At 50:1, 1 US gallon (128 fl oz) needs 2.6 fl oz of oil, and 5 litres need 100 ml. Most current handheld tools from major makers specify 50:1. Older engines and some brands use 40:1 or 32:1.
Quick reference
| 1 US gal | 2.6 fl oz | 3.2 fl oz | 4.0 fl oz |
| 2.5 US gal | 6.4 fl oz | 8.0 fl oz | 10.0 fl oz |
| 1 litre | 20 ml | 25 ml | 31 ml |
| 5 litres | 100 ml | 125 ml | 156 ml |
Use the ratio in your tool manual. Too little oil can seize the engine and too much fouls the plug.
Questions
Can I use car engine oil?
No. Use oil made for air-cooled two-stroke engines, usually labelled JASO FD or ISO-L-EGD.
How long does mixed fuel keep?
Many makers suggest using it within about 30 days unless you add a stabiliser.
Injury data for these tools
Lawn mowers (walk-behind & unspecified)Laceration68,019
Chain sawsLaceration29,535
Riding mowers & garden tractorsFracture16,479
String trimmers & brushcuttersLaceration16,067
Log splittersLaceration7,482
Leaf blowersFracture7,366ER visits in 2025
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