40:1 Mix Ratio Calculator
Easily calculate the exact amount of 2-stroke oil needed for your fuel. Perfect for chainsaws, strimmers, outboard motors, and any 40:1 petrol-to-oil mix requirements in the UK.
Fuel & Oil Details
Enter your fuel volume to calculate the exact 2-stroke oil required for a 40:1 mix
How much unleaded petrol do you have?
Select the unit of measurement for your fuel.
Choose how you want the oil amount displayed.
40:1 Mix Calculation
Exact 2-stroke oil required for your fuel volume
Enter your fuel volume above, then click Calculate Mix to see the exact oil required.
Common 2-Stroke Mix Ratios
Different engines require different fuel-to-oil ratios. Always check your manufacturer’s manual, but here are the most common ratios used in the UK.
| Mix Ratio | Oil per 5 Litres | Common Applications |
|---|---|---|
| 50:1 | 100 ml | Modern strimmers, brush cutters, small engines |
| 40:1 | 125 ml | Chainsaws, older strimmers, outboard motors |
| 32:1 | 156 ml | Classic motorcycles, vintage garden equipment |
| 25:1 | 200 ml | Very old 2-strokes, high-load industrial tools |
2-Stroke Fuel FAQ
Everything you need to know about mixing 2-stroke fuel, engine lubrication, and maintaining your petrol-powered garden equipment.
A 40:1 mix ratio means 40 parts of unleaded petrol to 1 part of 2-stroke engine oil. For every 1 litre (1000ml) of petrol, you need to add exactly 25ml of oil. This ratio is commonly required for many modern chainsaws, strimmers, and brush cutters to ensure proper engine lubrication without causing excessive carbon buildup.
The most accurate way is to use a dedicated measuring jug or a syringe/burette marked in millilitres (ml). Many 2-stroke oil bottles come with built-in measure-and-pour spouts. Avoid guessing or using random household spoons, as an incorrect mix can severely damage your engine.
If there is too little oil in the mix, the engine will not receive adequate lubrication. This causes excessive friction, overheating, and can quickly lead to catastrophic engine failure, such as a scored cylinder or seized piston. It is always better to be slightly rich on oil than too lean.
While slightly too much oil is safer than too little, it will cause the engine to run poorly, smoke excessively, and foul the spark plug. Over time, a too-rich oil mix can lead to heavy carbon deposits in the exhaust port, muffler, and piston crown, reducing performance and potentially causing overheating.
Mixed 2-stroke fuel should ideally be used within 30 days. Over time, the petrol degrades, loses its volatility, and can form varnishes or gums that clog carburettors. If you need to store it longer, use a fuel stabiliser, but it is best practice to only mix what you need for the job.