2-Stroke Fuel Mix Calculator
This 2-stroke fuel mix calculator tells you exactly how much oil to add to your gasoline to obtain the correct fuel-oil mixture for a two-stroke engine. Just enter how many liters of petrol you are preparing and the mix ratio recommended by the manufacturer — such as 50:1, 40:1 or 25:1 — and it instantly returns the amount of oil in milliliters. It is ideal for motorcycles, chainsaws, brush cutters, string trimmers, leaf blowers, outboard boat motors and any other equipment that runs on a premixed gasoline-and-oil blend.
Oil to add
Always use the mix ratio specified by your engine manufacturer. An incorrect mix can damage the engine: too little oil reduces lubrication, while too much oil fouls the spark plug and produces smoke.
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How it works
A two-stroke engine has no separate oil sump, so the lubricating oil must be mixed directly into the fuel. The mix ratio X:1 means X parts of gasoline for 1 part of oil. To find the oil, the calculator converts the fuel from liters to milliliters (1 liter = 1000 ml) and divides by the ratio: oil (ml) = liters × 1000 ÷ ratio. For example, 5 liters of petrol at 50:1 needs 5 × 1000 ÷ 50 = 100 ml of oil. At 40:1 the same 5 liters would need 125 ml, and at 25:1 it would need 200 ml — the smaller the first number, the more oil per liter of fuel.
How much oil for each mix ratio
The amount of oil depends only on the ratio: to turn it into milliliters per liter of petrol, divide 1000 by the first number (at 50:1 that is 20 ml/L, at 25:1 it is 40 ml/L). This table sums up the most common ratios with the oil needed for 1 and for 5 liters of fuel. Ratios with a smaller first number (20:1, 25:1) carry more oil and are typical of older or heavily loaded engines; 50:1 is standard on modern equipment.
| Ratio | Oil per 1 L | Oil per 5 L |
|---|---|---|
| 50:1 | 20 ml | 100 ml |
| 40:1 | 25 ml | 125 ml |
| 33:1 | 30.3 ml | 151.5 ml |
| 25:1 | 40 ml | 200 ml |
| 20:1 | 50 ml | 250 ml |
Why you should respect the manufacturer's ratio
A two-stroke engine is lubricated by the very oil dissolved in the petrol, so the proportion is not a minor detail. If the mix is lean (too little oil), the moving parts do not get enough lubrication: the engine overheats, the piston scores and, in the worst case, seizes. If the mix is rich (too much oil), the excess lubricant does not fully burn: bluish smoke appears, the spark plug fouls and carbon builds up in the exhaust and combustion chamber. That is why it is best to measure the oil with a syringe or dosing bottle rather than by eye, and to always follow the value stated in the tool's manual.
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Preguntas frecuentes
- What does a ratio like 50:1 mean?
- A 50:1 ratio means 50 parts of gasoline for every 1 part of oil. In practical terms, for each liter of petrol (1000 ml) you add 1000 ÷ 50 = 20 ml of oil. So 5 liters at 50:1 need 100 ml of oil, and 10 liters need 200 ml.
- How much oil do I add per liter of fuel?
- Divide 1000 by the first number of the ratio. At 50:1 that is 20 ml of oil per liter, at 40:1 it is 25 ml per liter, and at 25:1 it is 40 ml per liter. Multiply that figure by the number of liters you are mixing to get the total oil.
- What happens if I use the wrong ratio?
- Too little oil starves the engine of lubrication and can cause overheating, scoring or seizure. Too much oil leads to excessive smoke, spark-plug fouling and carbon build-up. Always follow the ratio in your owner's manual rather than guessing.
- Can I use car engine oil for a 2-stroke mix?
- No. Two-stroke engines require oil specifically formulated to burn with the fuel (labeled 2T, TC or JASO FB/FC/FD). Ordinary 4-stroke car oil is not designed to be burned and will damage a two-stroke engine, so always use a dedicated two-stroke oil.
- What are typical mix ratios for different tools?
- Many modern chainsaws and trimmers use 50:1, older equipment often specifies 40:1 or 32:1, and some vintage or high-load engines call for 25:1. The correct ratio depends on the engine and the oil, so check the tool's label or manual and use this calculator with that value.