Two-stroke engines in chainsaws, trimmers, outboards and dirt bikes are lubricated by oil mixed into the fuel. Too little oil scores the cylinder; too much fouls plugs and smokes. Always use the ratio in the owner’s manual – most modern equipment uses 50:1, older engines 32:1 or 25:1.
How to use the Gas Oil Ratio Calculator
- Mix ratio (gas : oil)
- Custom ratio
- Gas (petrol) volume
- Every result field is editable: type into Oil to add and Gas (petrol) volume plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the ratio (or enter your own) and the amount of gas. Type an oil amount into the result to find how much gas it mixes with.
Oil per amount of gas
| Gas | 25:1 | 32:1 | 40:1 | 50:1 |
|---|---|---|---|---|
| 1 US gal | 5.1 fl oz | 4.0 fl oz | 3.2 fl oz | 2.6 fl oz |
| 2.5 US gal | 12.8 fl oz | 10.0 fl oz | 8.0 fl oz | 6.4 fl oz |
| 5 US gal | 25.6 fl oz | 20.0 fl oz | 16.0 fl oz | 12.8 fl oz |
| 1 L | 40 mL | 31 mL | 25 mL | 20 mL |
| 5 L | 200 mL | 156 mL | 125 mL | 100 mL |
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| Mix ratio (gas : oil) | Choose one: 50 : 1, 40 : 1, 32 : 1, 25 : 1 … |
| Custom ratio | A number |
| Gas (petrol) volume | Units: US gal, L, UK gal |
Formula
Oil = gas volume ÷ ratioTotal mix = gas + oilWorked example
Inputs — Mix ratio (gas : oil): 50 : 1; Custom ratio: 60; Gas (petrol) volume: 1 US gal.
Results — Oil to add = 2.56 fl oz; Total mixture = 1.02 US gal.
Frequently asked questions
How much oil for 1 gallon at 50:1?
2.6 fl oz (76 mL).
How much oil per litre at 40:1?
25 mL.
Can I store mixed fuel?
Use it within about 30 days, or add a fuel stabiliser; ethanol blends absorb water over time.
What formula does the Gas Oil Ratio Calculator use?
Oil = gas volume ÷ ratio.