The amount of gas available for mixing determines the calculated amount of oil required. Consult the manual for the manufacturer's preferred gas-to-oil ratio for its equipment. Convert the gas from gallons into ounces, since two-cycle oil is calibrated in ounces. Divide the ounces of gas by the manufacturer's gas-to-oil ratio, and round off the result to the nearest half or whole number.
Most tools, recreational and transportation machinery with two-cycle engines have gas-to-oil ratios ranging from 20:1 to 80:1. For a new two-stroke engine, there is a break-in period where a ratio that is double the normal is required. For example, in the case of a gas-to-oil ratio of 60:1, a ratio of 30:1 is required during the break-in period. This means that more oil is needed during the initial period of operation.
Experts advise that it is better to err towards excess oil rather than not having enough. Rideau-info.com provides gas-to-oil fuel mix charts that serve as an ideal reference for any two-cycle engine. During the process of mixing, it is advised to blend a gallon of gas with oil at a time to impede settling in the gas can and raising the chances of engine and carburettor deposits.