Mix to E85 (target 85% ethanol)

Enter your pump/tested ethanol percentage (typical 55–85) and how many gallons of that fuel you have. We’ll compute how many gallons of E98 to add to reach ~E85.

Method: Let the difference to E85 be (85 − tested) / 100. Multiply by gallons to get pure ethanol needed; divide by 0.13 to convert to E98 gallons (because 0.98−0.85 = 0.13); add back to original gallons. See the PDF for derivation.
Impressions since Jan 17, 2025 1:23am: 190,380
Calculations provided by Thomas Gartman, B.S. Mathematics. View details here.