# Two-stroke mix ratio

The proportion of petrol to two-stroke oil that a combustion chainsaw runs on, expressed as a ratio such as 50:1 or 40:1. The engine has no separate oil sump, so this mixture is the only lubrication the crankshaft and piston receive.

Source: https://chainsawdata.net/en/glossary/two-stroke-mix-ratio/
Site: ChainsawData (chainsawdata.net) — open technical specification database
Last updated: 2026-08-24
License: free to quote with attribution to chainsawdata.net

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Always use the ratio in your own manual: modern saws commonly specify 50:1 with a quality two-stroke oil, while some older or air-cooled designs call for richer mixes. Getting it wrong is expensive in both directions — too little oil seizes the engine, too much fouls the plug, coats the exhaust and costs power. Mix in a clean, marked can rather than by eye, and use fresh fuel, because pump petrol with ethanol separates and degrades within weeks; premixed alkylate fuel avoids that entirely and burns much cleaner. Never run straight petrol, even briefly.