How Do You Calculate the Gas to Oil Ratio for a Motor?

The manufacturer of engines that require a mixture of gasoline and oil calculates the correct ratio of gas to oil, which varies widely. The operator’s manual usually indicates the correct ratio for that engine, or the owner can obtain this information from the retailer or manufacturer.

A snow blower engine may require a 32 to 1 ratio, while an outboard motor engine may require a ratio of 50 to 1 but a ratio of 25 to 1 during an initial “break-in” period. Once the proper ratio is determined, the user must calculate the actual quantities of oil and gasoline to mix, which is typically a few ounces of oil per gallon of gasoline.

Websites such as have online calculators that perform the necessary unit conversions and allow the user to input the ratio and number of gallons of gasoline to determine the correct amount of oil to add. Other sites, such as, have tables that display the correct amounts of gasoline and oil for commonly used ratios. Because retailers generally sell motor oil by the quart and gasoline by the gallon, using online calculators and tables is much easier than calculating the correct amounts manually.

The fuel tanks of most equipment requiring oil mixed with fuel are usually small and require the fuel to be mixed before filling, so manufacturers suggest using a larger container for mixing the gasoline and oil and filling the fuel tank. Adding a fuel stabilizer helps prolong the fuel mixture’s shelf-life.