Calculate how much oil to add to gasoline for a 25 to 1 fuel mix, in fluid ounces or mL per gallon or liter, or find the gas for your oil.
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25 To 1 Ratio Formula
The calculator supports fuel-to-oil, oil-to-fuel, finished-mixture splitting, both directions of unit-free scaling, and checking a measured mix. Each uses the 25:1 ratio.
Fuel mix mode (find oil needed for a given fuel amount, or fuel matched to a given oil amount):
Scale mode (find the missing side of any 25:1 split):
Check mix mode (verify an existing mix):
Variables:
- fuel = volume of gasoline (any unit, converted internally to mL)
- oil = volume of two-stroke oil (any unit, converted internally to mL)
- big = the 25-part side of the ratio
- small = the 1-part side of the ratio
- ratio = actual fuel-to-oil ratio of a measured mix
Choose oil required, gasoline supported, or finished mixture in the Solve for menu. The two scaling choices use unit-free numbers. Check an existing mixture compares measured gasoline and oil volumes, then shows the arithmetic adjustment to reach 25:1. A finished batch contains 26 total parts: oil = total / 26 and gasoline = total × 25 / 26. A mathematical ratio does not establish whether two products are compatible.
Common 25:1 Volumes and Ratio Checks
Use these tables as a quick reference. The first shows oil needed at common fuel amounts. The second shows how to read the Check an existing mixture result. No equipment-safe tolerance is assumed.
| Fuel | Oil (mL) | Oil (US fl oz) |
|---|---|---|
| 1 US gal | 151.4 | 5.12 |
| 2 US gal | 302.8 | 10.24 |
| 2.5 US gal | 378.5 | 12.80 |
| 5 US gal | 757.1 | 25.60 |
| 1 L | 40.0 | 1.35 |
| 5 L | 200.0 | 6.76 |
| 10 L | 400.0 | 13.53 |
| Result | Reading | Action |
|---|---|---|
| 25:1 | Mathematical target | Confirm the equipment instructions |
| Above 25:1 | Lean on oil | Add oil |
| Below 25:1 | Rich on oil | Add fuel |
Examples and FAQ
Example 1. You have 2 US gallons of gasoline. Oil needed = 2 / 25 = 0.08 US gal, which is about 10.24 fl oz or 302.8 mL.
Example 2. You measured 1 gallon of fuel and added 8 fl oz of oil. Ratio = 128 fl oz / 8 fl oz = 16:1. That is rich on oil. To reach 25:1 with that 8 fl oz of oil, you need 8 × 25 = 200 fl oz of fuel total, so add another 72 fl oz (about 0.56 gal).
Is 25:1 the same as 4%? Yes. Oil is 1 part out of 26 total, but the conventional shorthand compares oil to fuel only, so oil volume equals fuel volume divided by 25, which is 4% of the fuel.
What engines use 25:1? Use this ratio only when the equipment manual specifies 25:1. Requirements depend on the engine and approved oil. For example, STIHL mixture guidance specifies a different ratio for its equipment and directs users to their product manuals.
Can I scale a non-fuel ratio? Yes. Choose Small side from large side or Large side from small side and use the same measurement unit for both quantities. Follow the product instructions to determine compatibility and whether a ratio is by mass or volume.
Does mix temperature matter? This calculator assumes additive measured volumes at a common temperature and does not model thermal expansion. Follow the equipment and fuel-container instructions for measuring, mixing, storage, and handling.
