Some owners run modern oils leaner in old engines; only do that if the engine or oil maker says it is safe.
How the fuel mix calculator works
FuelMixCalc treats a ratio such as 50:1 as 50 volumes of gasoline to 1 volume of oil. The oil needed is the gasoline divided by the ratio; the gasoline for a bottle of oil is the oil times the ratio; and the ratio of an existing mix is the gasoline divided by the oil. Everything is converted to millilitres first, using 1 US gallon = 128 US fl oz = 3.785 L, 1 imperial gallon = 4.546 L and 1 US fl oz = 29.57 ml.
Oil needed by ratio
| Ratio | fl oz per US gal | ml per US gal | ml per litre | ml per 5 L |
|---|---|---|---|---|
| 16:1 | 8 | 237 | 62.5 | 313 |
| 20:1 | 6.4 | 189 | 50 | 250 |
| 24:1 | 5.33 | 158 | 41.7 | 208 |
| 25:1 | 5.12 | 151 | 40 | 200 |
| 32:1 | 4 | 118 | 31.3 | 156 |
| 40:1 | 3.2 | 95 | 25 | 125 |
| 50:1 | 2.56 | 76 | 20 | 100 |
| 100:1 | 1.28 | 38 | 10 | 50 |
Mix in a clean, approved fuel can: add the oil, then half the gas, shake, then the rest of the gas and shake again. Mixed fuel keeps about 30 days unless you add a stabilizer, and ethanol-free or pre-mixed canned fuel lasts longer. Shake the can before each refill.
Use the ratio and the oil type (for example JASO FD or TC-W3 for outboards) your engine’s manual specifies. The wrong mix can damage an engine and void a warranty.
Frequently asked questions
How much oil for 1 gallon at 25:1?
5.12 US fl oz, about 151 ml.
How much oil per litre at 25:1?
40 ml.
What engines use 25:1?
Mostly older outboard motors, mopeds and lawn equipment; check the manual or the cap.
Is FuelMixCalc free?
Yes, with no sign-up or ads.
Are my settings saved?
Yes, in this browser only.