Octane Blending Calculator
Calculate blended octane rating from up to three gasoline component volumes and octane numbers.
About this calculator
Gasoline blending in the field is often approximated as a straightforward volume-weighted average of each component's octane rating, and that's the model this calculator uses: blend octane = (V₁×O₁ + V₂×O₂ + V₃×O₃) / total volume, for up to three components like reformate, straight-run naphtha, and isomerate. It's worth knowing this linear-blending assumption is a simplification refiners actually rely on for routine gasoline blending, but it isn't exact — real blending can show measurable nonlinear ("blending index") effects, particularly with oxygenates like ethanol or with components that interact chemically, so a finished-fuel lab test is still the final word before a batch ships. Beyond the blend number itself, the calculator flags whether you've hit your target octane and by how much (the octane gap), and — when you're working with just two components — solves the linear-blend equation in reverse to tell you exactly what percentage of the higher-octane component you'd need to hit a specific target exactly.
It also throws in a rough economic estimate: a $0.03-per-gallon premium for every octane number above 87 (a common baseline regular-grade octane), converted to barrels at 42 gallons per barrel, to give a ballpark sense of how much blend-value you're capturing or leaving on the table. Treat that premium figure as directional only — actual octane premiums move with market conditions and specific buyer contracts, not a fixed formula.
Inputs
Results
Blend Octane Rating
85 RON
How to Use This Calculator
- Enter Component 1 Volume, Component 1 Octane, and Component 2 Volume.
- Set Component 2 Octane, Component 3 Volume, and Component 3 Octane.
- Adjust Target Octane as needed.
- Review the Blend Octane Rating (RON) result.
- Use Octane Gap from Target (RON) and Meets Target to inform your decision.
How the result changes with Component 1 Octane
| Component 1 Octane | Blend Octane Rating |
|---|---|
| 50 | 60 RON |
| 75 | 72.5 RON |
| 130 | 100 RON |
What each input means
- Component 1 Volume
- Volume of the first blending component (e.g., reformate).
- Component 1 Octane
- Research Octane Number of the first component. Reformate is typically 95–102.
- Component 2 Volume
- Volume of the second blending component (e.g., straight-run naphtha).
- Component 2 Octane
- Research Octane Number of the second component. Straight-run naphtha is typically 65–75.
- Component 3 Volume
- Volume of an optional third component (e.g., isomerate). Set to 0 if only two components.
- Component 3 Octane
- Research Octane Number of the optional third component. Collected for the blend but has no effect on the result while Component 3 Volume is 0.
- Target Octane
- Desired octane rating for the finished gasoline blend.
What each result means
- Meets Target
- 1 = Yes, 0 = No
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersComponent 1 Volume = 5000, Component 1 Octane = 100, Component 2 Volume = 5000, Component 2 Octane = 70 = 7 input(s) provided
- Calculate Blend Octane Rating85 = 85
- Calculate Octane Gap from TargetOctane Gap from Target-6 = -6
- Calculate Meets TargetMeets Target0 = 0
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why is the blend octane just a volume-weighted average instead of something more complex?
The calculator uses blend octane = (V₁×O₁ + V₂×O₂ + V₃×O₃) ÷ total volume because linear blending by volume is the standard field approximation refiners use for routine gasoline blending decisions. It's simple and generally close enough for planning, but it's not exact — real components can interact non-linearly, so this number is a directional estimate, not a stand-in for a finished-fuel lab octane test.
How does the calculator figure out the required percentage of Component 1?
When Component 3's volume is zero, the calculator solves the two-component blend equation in reverse: requiredPct1 = (targetOctane − octane2) ÷ (octane1 − octane2), expressed as a percentage. This tells you exactly what share of the higher (or lower) octane component you need to land precisely on your target, but it only runs for genuine two-component blends — it stays at zero if you're using all three components or if the two octane numbers are equal.
What does the estimated octane premium value actually represent?
It's a rough economic signal, not a market price: the calculator applies a flat $0.03-per-gallon premium for every RON point the blend sits above 87 (a common baseline regular-grade octane), then multiplies by total volume converted to gallons (42 gal/bbl). Actual octane premiums move with market conditions, season, and buyer contracts, so treat this as directional only.
Why does the octane gap matter if my blend already meets the target?
The octane gap (blend octane minus target octane) tells you not just whether you passed, but by how much — a large positive gap means you're likely over-blending with premium-octane components you could redirect elsewhere at a lower cost, while a value near zero means you're right at the target with little margin for measurement or component variability. Meets Target only reports a yes/no; the gap quantifies how much room you actually have.
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