E85 Ethanol Mix Calculator
Find how much E85 and pump gas to hit a blend.
Default 85%
Default 10%
Results update as you type.
How it works
Performance and flex-fuel enthusiasts often blend E85 with regular pump gasoline to dial in a specific ethanol content, and this calculator tells you exactly how much of each to mix. You enter the target ethanol percentage you want, the total volume you are mixing, and optionally the actual ethanol content of your E85 and pump gas, and it returns the gallons of E85 and pump gas to combine. Blending matters because ethanol has a high octane rating and cooling effect that can support more boost or timing, but pure E85 may be too much for a given tune, so tuners target an intermediate blend like E30 or E50. The tricky part is that E85 is rarely exactly 85 percent ethanol; it varies seasonally and by region, often ranging from around 51 to 83 percent, and pump gas already contains up to 10 percent ethanol. This calculator lets you enter the real percentages for an accurate mix. The math is a standard mixing equation that finds the split producing your target when the two fuels combine. Always verify the final blend with an ethanol content tester, since fuel percentages vary, and never exceed what your engine and tune safely support. Enter your target ethanol content and tank volume to compute the E85 and pump-gas amounts.
E85 gallons = total × (target − pump%) / (E85% − pump%)
To reach a target ethanol content in a given total volume, the calculator solves a simple blend equation. The E85 volume equals the total volume times the difference between the target and the pump-gas ethanol percentages, divided by the difference between the E85 and pump-gas percentages. The remaining volume is filled with pump gas to complete the blend.
Source:Fuel blending
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter target ethanol content and total volume to mix.
- 2
Adjust the options
Adjust e85 ethanol content and pump gas ethanol content if they apply — sensible defaults are already set.
- 3
Read your result
E85 to add updates instantly as you type — no button to press.
Frequently asked questions
How do I mix E85 to a target ethanol content?
Decide your target ethanol percentage and total volume, then use the blend equation: E85 volume equals total times the target minus pump-gas ethanol, divided by E85 minus pump-gas ethanol. The rest is pump gas. The calculator solves this instantly when you enter your target, volume, and the actual ethanol content of each fuel.
Is E85 always 85 percent ethanol?
No. Despite the name, E85 ethanol content varies by season and region, often ranging from about 51 to 83 percent, with less ethanol in winter for cold starting. Pump gasoline typically contains up to 10 percent ethanol too. For an accurate blend, test or look up the actual percentages and enter them rather than assuming exactly 85 and 10.
Why blend E85 with regular gas?
Blending lets tuners target an intermediate ethanol content, such as E30 or E50, to gain ethanol's high octane and cooling benefits for more boost or timing without the drawbacks of full E85, like reduced range and cold-start issues. The right blend depends on the engine, tune, and goals, and must stay within what the setup safely supports.
How do I verify the final ethanol content?
Use an ethanol content tester, either a simple graduated test kit or an inline sensor, to measure the actual percentage after mixing. Because fuel percentages vary and mixing is not perfectly precise, verifying is important, especially for aggressive tunes that depend on a specific ethanol level for safe operation. Adjust the blend if the measured value differs.
Can any car run an E85 blend?
Only flex-fuel vehicles or cars with a compatible tune and fuel-system components should run high ethanol blends. Ethanol carries less energy per gallon and can affect fuel delivery, so a standard engine not designed or tuned for it may run poorly or be damaged. Always confirm your vehicle and tune support the blend before using it.