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Automotive Calculators

Octane Blend Calculator

2026-09-27 6 min

Resulting octane from mixing two fuels by volume — blend pump gas with race fuel or E85 precisely.

Blended Octane
98.7 octane
Total Volume
15.0 gal

Calculator

Fuel A Volume(gal)
gal
Fuel A Octane(octane)
octane
Fuel B Volume(gal)
gal
Fuel B Octane(octane)
octane
Results update live as you type

Live statistics

Blended Octane

98.7 octane

Total Volume

15.0 gal

Results

Optimal

Blended Octane

98.7octane

Total Volume

15.0gal

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

98.7Blended Octane
15Total Volume

Blended Octane vs. Fuel A Volume

Blended Octane

98.7octane
85115

Formula

Volume-weighted octane averaging — accurate within ~1 number for gasoline blends.

Blend = (galA × octA + galB × octB) ÷ total gallons

Variables

SymbolNameUnitDescription
galVolumesgalEach fuel’s share
octOctanes(R+M)/2Each fuel’s rating

Explanation

Ethanol blends deviate slightly from linear (favorable synergy) — treat results as conservative.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Fuel A Volume:10 gal
Fuel A Octane:93 octane
Fuel B Volume:5 gal
Fuel B Octane:110 octane
Result: 4 inputs ready
Step 2

Apply the formula.

Blend = (galA × octA + galB × octB) ÷ total gallons
Result: Primary result = 98.7 octane
Step 3

Read every derived output.

Blended Octane:98.7 octane
Total Volume:15.0 gal
Result: Blended Octane = 98.7 octane
Final Answer
98.7

Worked Examples

See how the calculator works with different scenarios.

Scenario

10 gal of 93 + 5 gal of 110.

Inputs

A:10 gal @ 93
B:5 gal @ 110

Calculation

(930 + 550) ÷ 15 = 98.7

Result

98.7 octane, 15 gallons.

Interpretation

Covers a 96-requirement combo with margin to spare.

Understanding Your Result

Your Result: Blended Octane: 98.7 octane

What This Means

Octane of your mixed tank.

Why It Matters

Stretch expensive race fuel with pump gas to exactly the requirement — no more, no less.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

  • •Double-check units on every input before trusting the result
  • •Compare against the worked example below to sanity-check magnitude
  • •Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Blending is weighted-average chemistry — measure volumes, weight the octanes, hit the target.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

  1. Fill to first click at the same pump, record the odometer (Tank 0).
  2. Drive normally for 2–3 tanks; always refill to first click at the same pump.
  3. MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
  4. Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
  5. Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

  • •Start from the default values — they describe a typical combination
  • •Use the sensitivity chart to see which input moves the result most
  • •Keep units consistent (all inches or all mm, never mixed)

Common Mistakes

Mixing units (inches with mm, psi with kPa)
Convert every input to the unit shown on its field before calculating.
Trusting a single output blindly
Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.
Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.
No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

Linear blending accurate?
Within ~1 octane number for gasolines; ethanol blends often test slightly higher (bonus).

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG
Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km
Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe
Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE
Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance
Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag
Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling
Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II
On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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