40:1 Fuel Mix Chart – 2-Stroke Gas to Oil Ratio Guide
Mixing fuel at a 40:1 ratio is a common requirement for many older two-stroke engines. This ratio ensures your engine runs smoothly, stays well-lubricated, and avoids long-term damage. On this page, you’ll find everything you need to know about premix ratios, how to mix correctly, and quick-reference charts for both US and metric measurements.
What Is a 40:1 Fuel Mix?
A 40:1 fuel mix means 40 parts gasoline to 1 part 2-stroke oil. This is slightly richer in oil than the 50:1 mix, making it ideal for older or high-performance engines that need a bit more lubrication.
For example:
- 1 gallon of gas (128 oz) mixed with 3 oz of oil equals a 40:1 mix.
- 1 litre of gas mixed with 25 millilitres of oil also gives you a 40:1 mixture.
Using the correct fuel ratio is essential for avoiding overheating, wear, and carbon buildup.
Why Use a 40:1 Mix?
This ratio is often recommended for:
- Older 2-stroke engines that were built before synthetic oils became widely available.
- High-RPM tools that require extra lubrication.
- Engines running under heavy loads or hot conditions.
Using the proper oil ratio helps:
- Extend engine life
- Improve combustion
- Prevent piston scoring and overheating
To make it easier you can use the following old school reference charts.
Metric (Litres:Millilitres)
| Fuel (L) | Oil (mL) |
|---|---|
| 1 | 25 |
| 2 | 50 |
| 3 | 75 |
| 4 | 100 |
| 5 | 125 |
| 7.5 | 188 |
| 10 | 250 |
| 15 | 375 |
| 20 | 500 |
| 25 | 625 |
US (Gallons:Fluid Ounces)
| Fuel (gal) | Oil (fl oz) |
|---|---|
| 1 | 3 |
| 1.5 | 5 |
| 2 | 6 |
| 2.5 | 8 |
| 3 | 10 |
| 4 | 13 |
| 5 | 16 |
| 7.5 | 24 |
| 10 | 32 |
| 15 | 48 |
How to Mix Gas and Oil Safely
- Use a clean, approved fuel container.
- Measure oil precisely—don’t guess.
- Pour oil into the container first, then add gasoline.
- Seal and shake to mix thoroughly.
- Label the container with the mix ratio and date.
Tip: Mix only what you’ll use within 30 days to maintain fuel freshness.
Recommended Tools and Supplies
- Fuel mixing jugs with ratio markings
- 2-stroke oil measuring bottles
- Digital fuel mix calculators or apps
- High-quality 2-cycle oil (e.g., Stihl, Echo, Husqvarna, or marine-grade brands)
2 Stroke Mix App
If you’re looking for something to help with other ratios and remind you how old your fuel is, please take a look at our app for iPhone and Apple Watch on the App Store?
FAQs About 40:1 Mix
Q: Is 40:1 the same as 50:1?
A: No. 40:1 uses more oil than 50:1, making it slightly richer. Using too much oil might result in more smoke but offers extra protection. Never go leaner (less oil) than the recommended ratio. Always consult the manual for the correct ratio for the specific engine.
Q: Can I use synthetic 2-stroke oil?
A: Yes! High-quality synthetic oil burns cleaner and provides excellent protection. Just be sure it’s labeled for air-cooled 2-stroke engines.
Q: What engines use 40:1?
A: You’ll typically find this richer mix recommended for:
- Older chainsaws and trimmers
- Leaf blowers and hedge trimmers
- Some vintage motorcycles and mopeds
- Older outboard motors