How ratios work
A 50:1 mix means fifty parts gasoline for every one part two-stroke oil - by volume, not weight.
For one US gallon (128 fluid ounces) of gasoline at 50:1, you need 128 ÷ 50 = 2.56 fl oz of oil. For the same gallon at 100:1, it’s 1.28 fl oz. The math scales linearly with both ratio and tank size.
oil_oz = fuel_oz ÷ ratio
Frequently asked
What ratio does my equipment need?
The owner’s manual is the only authoritative source. Most modern Stihl, Husqvarna, and Echo equipment runs 50:1. Older saws and many vintage outboards want 32:1 or 24:1. Some premium synthetics support 100:1 in equipment originally specced at 50:1 - but only with manufacturer approval.
Can I run 50:1 in a 32:1 engine?
Not safely. The engine was designed for a specific oil film at high RPM. Running leaner reduces protection and increases wear. Err richer when in doubt - extra oil just smokes; not enough seizes.
How long does mixed fuel last?
Mixed two-stroke fuel begins separating and degrading within 30 days. With ethanol-free gas and fuel stabilizer, you can stretch it to a few months. Most pros mix only what they’ll use in a week or two.