E85 Fuel Calculator

Mixing E85 with regular gasoline to hit a specific ethanol blend (like E30 or E50) requires precise ratios — the E85 Fuel Calculator works out exactly how much of each fuel to pump. Enter your total fuel needed, target ethanol content, fuel properties (E85 ethanol content, regular gas ethanol content, and octane ratings), and current prices per gallon to get the exact gallons of E85 and regular gas needed. Secondary outputs include your blend octane rating, total fill-up cost, and effective cost per gallon.

gallons

How many gallons you want to add to your tank

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Desired ethanol percentage (E30, E50, etc.)

%

Actual ethanol content in E85 (varies by season)

%

Ethanol content in regular gasoline (usually E10)

E85 typically has 105-108 octane

per gallon
per gallon

Results

E85 Needed

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Regular Gas Needed

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Blend Octane Rating

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Total Fill-up Cost

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Effective Cost per Gallon

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Frequently Asked Questions

What is E85 fuel and why use it?

E85 is a fuel blend containing 85% ethanol and 15% gasoline. It offers higher octane ratings (105+) compared to regular gas, allowing for more aggressive tuning and potentially more power in flex-fuel or modified vehicles.

Can any car use E85 fuel?

Only flex-fuel vehicles (FFV) or properly modified cars can safely use E85. Regular vehicles require fuel system modifications including compatible fuel lines, injectors, and engine tuning to handle ethanol blends.

Why does E85 ethanol content vary?

E85 ethanol content varies seasonally and by region, typically ranging from 70-85%. Winter blends may have lower ethanol content for cold-weather starting, while summer blends are closer to 85%.

How do I calculate the right mix for my tune?

Use your tuner's specified ethanol percentage (like E30 or E50). Enter this as your target content, along with your fuel amounts and the actual ethanol content of available fuels to get precise mixing ratios.

Is E85 more cost-effective than regular gasoline?

E85 is typically cheaper per gallon but provides 15-25% lower fuel economy. The cost effectiveness depends on the price difference and your vehicle's efficiency on ethanol blends.

What octane rating will my ethanol blend have?

Ethanol blends increase octane ratings significantly. E30 typically provides 91-93 octane, while E50 can reach 95-98 octane, depending on the base gasoline octane rating.

How accurate do ethanol mix ratios need to be?

For optimal performance and engine safety, aim for within 2-3% of your target ethanol content. Most modern engine management systems can adapt to small variations in ethanol content.