2-Cycle Oil Mix Calculator

A mix ratio is written as gas:oil, so 50:1 means 50 parts gasoline to 1 part oil. To find the oil, you divide the fuel by the ratio. One US gallon is 128 fluid ounces, so 128 ÷ 50 = 2.56 oz per gallon; one litre is 1000 ml, so 1000 ÷ 50 = 20 ml per litre.

The other common ratios come from the same division: 40:1 is 3.2 oz per gallon and 32:1 is 4 oz. The calculator does that arithmetic in both unit systems at once, and it works in reverse too, for when you know how much oil you have and want to know how much gas it will treat.

The short answer is whatever the decal on the fuel cap or the owner's manual says. As a general guide, modern handheld tools (Stihl, Husqvarna, Echo and Makita chainsaws, trimmers and blowers) are 50:1; equipment from the 1970s through the 1990s is often 40:1; vintage machines and older Lawn-Boy mowers are 32:1; and older outboards and some break-in schedules call for 25:1.

When you are torn between two ratios, take the richer one. Too much oil fouls a plug and sooties an exhaust, which a cleaning reverses. Too little oil removes the lubricating film and scores a piston, which no cleaning fixes.

• Use fresh 89 octane or higher, ethanol-free where you can get it.
• Measure the oil into the empty can and add the gas second, so pouring stirs the mixture.
• Seal the can and shake it before filling the tank.
• Mix only what you will burn within a month, and label the can with the ratio and the date.
• Use a real 2-stroke oil carrying the rating your engine calls for: JASO FD for air-cooled, NMMA TC-W3 for water-cooled outboards. Never car engine oil.