Figure out exactly how much E85 and pump gas to add at the pump to hit your target ethanol blend. Works in gallons or liters.
Ethanol content changes fuel properties and the fuel mass required for a commanded lambda. It does not create one universally safe boost, timing, or blend target. Enter only a mixture supported by the vehicle and calibration, and verify fuel pressure, injector duty, trims, and measured ethanol content where applicable.
Enter the target range specified for the exact vehicle and tune. Platform names or modification stages are not enough to establish a compatible ethanol content.
US fuel sold as E85 can contain 51% to 83% ethanol and varies by season and location. If you are mixing to a tight target without a flex-fuel sensor, test the pump fuel and enter the measured value in “Pump E85 Actual Content.”
Only add fuels approved for the vehicle, avoid overfilling, and allow the contents to mix before relying on a measured ethanol value. The blend changes fuel requirements; use only a calibration designed for that range and follow its verification process. The AFR/Lambda calculator explains how fuel-referenced AFR changes with stoichiometry.
Ethanol-rich fuel has different stoichiometry, density, and energy content from gasoline. Required volumetric flow therefore changes with actual content, base gasoline, target lambda, and calibration; it should not be assumed to be one fixed percentage. Use the injector calculator as a planning aid, then validate the entire fuel system under load.
Say you have 5 gallons of E10 already in a 15-gallon tank and you want to land at E30 on a full tank. You have 10 gallons of space to fill. Your pump E85 tested at 80% ethanol (a realistic real-world reading rather than the 85% on the sign), and the pump gas is E10. The total ethanol you need in a full 15-gallon tank at E30 is 15 × 0.30 = 4.5 gallons of pure ethanol. The 5 gallons of E10 already contribute 5 × 0.10 = 0.5 gallons. So the 10 gallons you add must supply the remaining 4.0 gallons of ethanol.
Adding about 4.3 gallons of the 80% E85 and 5.7 gallons of E10 lands the full tank right at E30. Notice that if you had assumed the pump fuel was a true 85% instead of the tested 80%, you would have added too little E85 and come up short of your target - which is exactly why testing the actual content, or running a flex fuel sensor, matters when you are aiming for a tight blend.
The result is a volume-weighted ethanol calculation and assumes the entered volumes and measured contents are accurate. See the U.S. Department of Energy's E85 fuel overview. Only use a blend supported by the calibration and fuel system; this calculator does not determine what ethanol content is safe for a vehicle.
Use only the ethanol range supported by the vehicle and calibration. There is no universal best blend because fuel-system capacity, materials, sensors, cold-start strategy, and tune requirements vary.
US E85 can contain 51% to 83% ethanol and varies by season and location. If the vehicle does not measure ethanol content, test the batch before aiming at a tight target.
Ethanol-rich fuel has different stoichiometry, density, and energy content. Required volume depends on actual ethanol content, base fuel, lambda target, power, and calibration rather than one fixed percentage.
If your car has a flex fuel sensor the ECU reads ethanol content directly. Otherwise, use a graduated ethanol test kit: add a measured amount of water to a known volume of fuel, shake, let it settle, and read how much the water layer grew. The increase is the ethanol fraction, since ethanol mixes into the water and gasoline does not.
Use a volume-weighted average: resulting ethanol % = (Vol1 × %1 + Vol2 × %2) ÷ total volume. To solve for how much E85 to add to a known amount of pump gas, rearrange for the unknown volume. The calculator on this page does both the target-blend solve and the two-fuel mix automatically.
Seasonal ethanol content can change within the allowed E85 range. A flex-fuel system can measure that change; otherwise test the batch and stay within the exact calibration requirement.
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