Is octane blending truly linear?

For most pump-gas blends (87–93 octane range) the linear approximation is accurate within about 0.5 octane numbers. High-concentration oxygenate blends (E85, M100) or certain racing fuels can deviate slightly due to synergistic chemistry, but the linear rule is the industry-standard starting point.

What octane number does this tool calculate — RON, MON, or AKI?

The tool calculates blended AKI (Anti-Knock Index), also called pump octane (R+M/2), which is the number displayed on US fuel pumps. If you enter RON values the result will be a blended RON. The blending math is the same regardless of the octane scale you use.

Can I use this to mix more than two fuels?

The tool handles two fuels in one step. To blend three fuels, first blend fuels 1 and 2, note the result and combined volume, then blend that result with fuel 3.

Does adding higher-octane fuel always eliminate knock?

Higher octane raises the knock threshold, but knock can also be caused by heat soak, carbon deposits, ignition timing, lean air-fuel ratio, or intake air temperature. Octane blending addresses fuel quality only — other factors need separate attention.

How much 100-octane fuel do I need to raise 93 octane to 95?

Use the "target octane" mode in the tool. For example, to hit 95 with a 93/100 blend you need roughly 28.6% of the volume in 100-octane fuel and 71.4% in 93-octane fuel.

Octane Blend Calculator

Enter the octane ratings and volumes of two fuels to calculate the blended octane rating instantly.

Calculator Mode

Unit:

Fuel A

Octane Rating (AKI / pump octane)

Volume

Fuel B

Octane Rating (AKI / pump octane)

Volume

Enter your fuel values and click Calculate

Summary

This tool computes the blended octane rating of two fuels mixed in a known volume ratio. The calculation uses the linear blending rule: (octane_A × volume_A + octane_B × volume_B) / (volume_A + volume_B). This is the standard method for estimating pump-octane (R+M/2) of a blend and is accurate enough for street and mild performance applications. Race-fuel blending at high concentrations may deviate slightly due to non-linear synergistic effects.

How it works

Enter the octane rating of your first fuel (e.g., 87 for regular pump gas).
Enter the volume of the first fuel in gallons or liters.
Enter the octane rating of your second fuel (e.g., 93, 100, or 110).
Enter the volume of the second fuel in the same unit.
The tool calculates the blended octane rating and shows the volume proportions.

Use cases

Estimate the octane of a pump gas blend when 91 is unavailable.
Calculate how much race fuel to add to pump gas to hit a target octane.
Verify a mixed tank meets the minimum octane requirement of a turbocharged engine.
Plan a cost-effective fuel strategy using partial fills of premium fuel.
Check the result of accidentally mixing two different fuel grades.
Determine the proportion needed to achieve a specific target octane rating.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu