Octane Mix Calculator

The Octane Mix Calculator helps you blend two fuels to a target octane rating. Tell it the octane of your two fuels and either the octane you are aiming for — to get the exact recipe of how much of each to pour — or two known volumes, to see the octane you will end up with. It uses the standard volume-weighted blending model and shows the mix ratio, an animated mixing tank, an octane number line, and the full step-by-step working so you can trust the numbers before you pour.

How Octane Blending Works

Octane numbers do not add — they average by volume. When you combine two fuels, each contributes its octane in proportion to its share of the tank. That gives the simple, reliable formula below, which is how anyone from racers to refinery blenders estimates a mix.

To go the other way — from a target octane to a recipe — rearrange the same equation to solve for the fraction of the higher-octane fuel you need:

Here \(f_A\) is the fraction of Fuel A by volume. Multiply it by your total desired volume to get how much high-octane fuel to add; the remainder is your base fuel. Because the result is a weighted average, the blend always lands between the two fuels — you can never blend higher than your highest fuel or lower than your lowest.

How to Use This Calculator

1. Enter both fuel octanes: Put your higher-octane fuel in Fuel A and your base fuel in Fuel B, using the same standard (AKI, RON, or MON) for both.
2. Pick a mode: Choose Find the mix to enter a target octane and total volume, or Check a blend to enter two known volumes.
3. Enter your target or volumes: For Find the mix, add the target octane and how much total blend you want. For Check a blend, add how much of each fuel you are pouring.
4. Calculate: Read off the recipe or blended octane, the mix ratio, the octane number line, and the step-by-step breakdown.

Common Octane Ratings (Reference)

Approximate octane values you can plug in. Pump grades vary by country and altitude, and race fuels vary by brand — always check the label.

Popular Uses

Accuracy & Safety Notes

• Linear model: Real fuels blend slightly non-linearly, especially with ethanol and other oxygenates. The result is a close estimate, not a lab value.
• Match the standard: Enter both fuels using the same rating system. Mixing an AKI number with a RON number gives a meaningless result.
• Leaded vs unleaded: Leaded race fuel can damage catalytic converters and oxygen sensors. Only use it in engines designed or approved for it.
• Verify under load: When octane matters for engine safety, confirm with a knock sensor, data log, or octane tester — do not rely on math alone.

Frequently Asked Questions

How do you calculate the octane of a fuel blend?

Octane blends by volume. The blended octane equals (Volume A × Octane A + Volume B × Octane B) divided by the total volume. This volume-weighted average is the standard approximation used for mixing pump gas with race fuel or ethanol.

How much race fuel do I add to reach a target octane?

The fraction of the higher-octane fuel you need equals (Target − Fuel B octane) ÷ (Fuel A octane − Fuel B octane). Multiply that fraction by your total desired volume to get how much high-octane fuel to add, and the rest is your base fuel.

Can I blend fuels to get an octane higher than both?

No. Blending always produces an octane between the two fuels. The result can never be higher than your highest-octane fuel or lower than your lowest-octane fuel, because it is a weighted average of the two.

Is fuel octane blending really linear?

For most practical mixing it is treated as linear by volume, which is accurate enough for blending pump grades or adding race fuel. Real fuels have small non-linear blending effects, especially with oxygenates like ethanol, so treat the result as a close estimate and verify with a knock sensor or octane tester when precision matters.

What is the difference between AKI, RON, and MON?

RON (Research Octane Number) and MON (Motor Octane Number) are two lab test methods. AKI, the number on US pumps, is their average (RON + MON) ÷ 2. Europe posts RON. As long as you enter both fuels using the same standard, the blend math works the same.

Does mixing 87 and 93 give 90 octane?

Only if you mix them in equal amounts. Equal volumes of 87 and 93 average to 90. If you use more of one than the other, the blend shifts toward that fuel's octane in proportion to its share of the tank.

Additional Resources

• Octane Rating - Wikipedia
• Gasoline - Wikipedia