2 Stroke Oil Mix Calculator
5 min read · Updated 13 September 2026
Getting premix right is not complicated, but getting it wrong is expensive. Too little oil and the piston and big end run dry; too much and you foul plugs, load the exhaust and lose power.
Use the calculator above for the exact quantity, then check the chart below if you want the common numbers at a glance.
Calculator
2 Stroke Oil Mix Calculator
Oil required
125ml
4.23 fl oz of two-stroke oil into 5.00 litres of petrol for a 40:1 mix.
Always follow the ratio in your owner's manual or on your oil bottle. Mix in a clean, marked fuel can — never straight into the tank.
Premix chart: oil per litre of petrol
The maths is simple: oil in millilitres = litres of petrol x 1000 / the ratio number. So 5 litres at 40:1 is 5000 / 40 = 125 ml.
| Ratio | 1 litre | 5 litres | 10 litres | 20 litres |
|---|---|---|---|---|
| 20:1 | 50 ml | 250 ml | 500 ml | 1,000 ml |
| 25:1 | 40 ml | 200 ml | 400 ml | 800 ml |
| 32:1 | 31 ml | 156 ml | 313 ml | 625 ml |
| 40:1 | 25 ml | 125 ml | 250 ml | 500 ml |
| 50:1 | 20 ml | 100 ml | 200 ml | 400 ml |
| 60:1 | 17 ml | 83 ml | 167 ml | 333 ml |
| 80:1 | 12.5 ml | 62.5 ml | 125 ml | 250 ml |
Which ratio should you run?
- Follow the owner's manual or the oil bottle first — modern synthetic oils and modern motors are usually happy at 40:1 or 50:1.
- Older air-cooled and pre-mix-hungry engines often call for 32:1 or richer.
- Racing hard, high revs and hot weather favour a slightly richer mix (more oil, lower number).
- Never mix ratios in the same can, and never guess — an unlabelled can is the most common way a bike ends up run on straight petrol.
How to mix it properly
- Mix in a clean, sealed fuel can, never directly in the tank — oil needs fuel to carry it.
- Pour the oil in first, add roughly half the petrol, swirl, then top up and swirl again.
- Label the can with the ratio and the date in permanent marker.
- Use premix within about a month. Petrol goes off, and stale fuel jets badly and gums carburettors.
Signs your mix is wrong
If you are unsure what went into the tank, drain it and start again. A fresh can of fuel is a lot cheaper than a top end. Keep your fuel, hours and jetting notes in one place — see our dirt bike service intervals guide for what else to track.
| Symptom | Likely cause |
|---|---|
| Heavy smoke, oily exhaust, fouled plugs | Too much oil (ratio too rich) |
| Bogging low down, dropping revs | Too much oil or stale fuel |
| Overheating, seizure, scored piston | Too little oil (ratio too lean) |
| Pinging under load | Lean mix or wrong fuel octane |
Common questions
How much 2 stroke oil to 5 litres of petrol?
At 40:1 you need 125 ml of two-stroke oil in 5 litres of petrol. At 50:1 it is 100 ml, and at 32:1 it is roughly 156 ml.
How much oil per litre at 50:1?
20 ml of two-stroke oil per litre of petrol. Divide 1000 by the ratio number to get millilitres per litre.
What happens if I put too much oil in my 2 stroke?
It will smoke heavily, foul plugs, run rich and lose power, and carbon will build up in the exhaust. It is far less damaging than too little oil, but it still needs correcting.
Can I mix 2 stroke fuel in the tank?
No. Always mix in a separate can so the oil is fully blended before it reaches the engine. Mixing in the tank leaves pockets of neat petrol.
How long does premix last?
Around a month in a sealed can. After that the petrol starts to go off, which causes poor starting and blocked jets.
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