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E85 Mix Calculator
Blend gasoline and E85 to a target ethanol content
The E85 mix calculator finds the ethanol percentage, and the stoichiometric air/fuel ratio, that result from blending two fuels.
Formula: Blend % = (V₁×E₁ + V₂×E₂) ÷ (V₁ + V₂) · Blend stoich ≈ weighted AFR
What this number means
This calculates how much E85 and gasoline to combine for a target ethanol percentage, accounting for the ethanol already in pump gasoline. It also works backwards to find the content of a mix you already made.
What to change next
Test your pump E85 first and enter its real content, not the 85 on the sign — seasonal blends vary widely. Retune fueling when the target content changes by more than a few points.
Worked example
To make 10 gallons at 50% ethanol from E85 tested at 80% and gasoline at 10%, mix ≈ 5.7 gallons of E85 with ≈ 4.3 gallons of gasoline.