Frequently Asked Questions

It depends on what's actually in the pump and what gasoline you're mixing with. With E80 pump fuel and E10 gasoline in a 15-gallon tank, roughly 8.6 gallons of E85 and 6.4 gallons of 93. Use the calculator above with your real numbers.

No. ASTM D5798 allows 51–83% ethanol in every class and season. Warm-climate states typically run near the top of that range year round; cold-winter states drop lower in winter for cold-start reasons. Nothing labeled E85 is required to contain 85% ethanol — in fact the standard caps it at 83%.

Yes, that's the most common way to reach a target blend like E30 or E50. The calculator handles the gasoline's own ethanol content — most pump 93 is E10, around 9.8% ethanol, which shifts the math more than people expect.

Choose "Fix my current blend." If there's room in the tank you can simply add gasoline. If the tank is full, the calculator tells you how much to drain, or how far to burn it down first, and what each option gets you.

For a non-flex-fuel vehicle, yes — ethanol needs substantially more fuel volume than gasoline, and running it without a calibration that accounts for that risks a dangerously lean condition. Flex-fuel vehicles handle it natively. This calculator does not confirm whether your vehicle or fuel system can handle a given blend.

Yes — the gal/L toggle switches every volume. The engine works in liters internally, so there's no conversion drift either way.

The calculator runs entirely in your browser with no network calls, so once the page has loaded it keeps working with no signal. The station finder will need a connection for live data.