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Octane Number Blending Calculator

Work out octane number blending instantly with clear inputs, formula shown and shareable results.

About Octane Number Blending Calculator

Octane numbers blend approximately linearly by volume, so the blend rating is the volume-weighted average of the components. Sixty litres of 91 with forty litres of 98 gives 93.8. Real refinery blending uses blending octane numbers that differ slightly from the neat values because components interact, but volumetric averaging is the standard first estimate.

Formulas

Volumetric blend

octane = (V1 x O1 + V2 x O2) / (V1 + V2)

Volume share

share = V1 / (V1 + V2)

Worked example

With the default values below, Octane Number Blending Calculator returns Blended Octane Rating of 93.80. Change any input above and every figure here is recalculated in your browser.

Inputs used

Volume of the first fuelminimum 0 L
60 L
Octane rating of the first fuelminimum 0
91
Volume of the second fuelminimum 0 L
40 L
Octane rating of the second fuelminimum 0
98

Results

Blended Octane Rating
93.80
Total Blend Volume
100.00 L
Share Of The First Fuel
60.00%
Gain Over The Lower-Rated Fuel
2.80

Step by step

  1. 1Values used
  2. 2Volumetric blend
  3. 3Volume share
  4. 4Blended Octane Rating= 93.80
  5. 5Total Blend Volume= 100.00 L
  6. 6Share Of The First Fuel= 60.00
  7. 7Gain Over The Lower-Rated Fuel= 2.80

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is octane blending really linear?

Close but not exactly. Aromatics and ethanol show non-linear blending, so refiners use empirically corrected blending values for precise work.

Does a higher octane number mean more energy?

No. Octane measures resistance to knock, not energy content. High-octane petrol often carries slightly less energy per litre.

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