Gas Oil Ratio Calculator (2-Stroke)

2-Stroke Fuel Mixing: Why It Matters

Unlike 4-stroke engines, 2-stroke engines do not have a separate oil reservoir. The oil that lubricates the engine’s pistons, bearings, and cylinder walls must be mixed directly into the gasoline before it enters the engine. Getting the ratio wrong has serious consequences.

The Formula Oil Volume = Gas Volume ÷ Ratio

For example, at 50:1: for every 50 parts of gasoline, you add 1 part of 2-stroke oil.

• 1 US gallon of gas at 50:1 → add 2.56 oz (75.7 mL) of oil
• 1 liter of gas at 50:1 → add 20 mL of oil

Common Ratios and When to Use Them Different engines require different ratios. Always check your owner’s manual. When in doubt, use a slightly richer mix (lower ratio number) rather than leaner, because running too little oil will destroy the engine.

• 50:1: Most modern 2-stroke equipment (chainsaws, string trimmers, leaf blowers, many dirt bikes, outboard motors). This is the most common ratio today.
• 40:1: Common on older equipment and some dirt bikes. Also used as a safe general-purpose ratio.
• 32:1: High-stress or older engines. Snowmobiles from the 1990s. Some Yamaha and Polaris outboards.
• 25:1: Very old or high-wear engines. Also recommended by many manufacturers during engine break-in.
• 16:1: Very old engines from the 1950s to the 1970s.

What Happens With Wrong Mix Ratios Too much oil (rich mix): excessive smoke from the exhaust, fouled spark plugs, carbon buildup in the exhaust port, reduced power, oily residue. Too little oil (lean mix): insufficient lubrication, overheating, piston seizure, permanent engine damage. A seizure can happen within minutes of starting.

The direction of the error matters far more than the size of it. Mixing 40:1 fuel into a saw that wanted 50:1 gives you 25% more oil than specified, and the worst you get is a smoky exhaust and a plug you clean sooner. Mixing 50:1 into a saw that wanted 32:1 leaves you 36% short of the oil the engine was designed around, and that one can end the engine. If you are guessing, guess rich.

Always Use Quality 2-Stroke Oil Use oils rated JASO FD, ISO-L-EGD, or API TC. Avoid substituting with motor oil, gear oil, or vegetable oil, which can damage seals and cause premature wear.

Bottle-First Mixing Most people work the other way round from this calculator: they have a bottle in hand and want to know how much gas it treats. Fill in the bottle size and the page answers that too. One 100 mL bottle makes 5 liters of 50:1 mix, which is the reason so many bottles are exactly that size. The 2.6 oz (77 mL) size sold in the US is the same idea in different units, cut to dose exactly one US gallon at 50:1.