Two-Stroke Fuel Mix Calculator

About this calculator

Two-stroke engines have no separate oil sump, so oil must be pre-mixed into the petrol at a specific ratio — this calculator computes oil needed = fuel volume ÷ ratio (a 50:1 ratio on 5 liters of petrol needs 100 ml of oil), scaling to whatever ratio the engine manufacturer specifies.

Owners of chainsaws, string trimmers, outboard motors, and mopeds use this before every fill-up, since running a two-stroke engine on straight petrol destroys it within minutes from lack of lubrication, while too much oil fouls spark plugs and leaves excess carbon deposits — getting the ratio exactly right matters more than with any four-stroke engine, where oil and fuel are always kept separate.