What Is a Fuel Percentage Calculator?

A fuel percentage calculator is a tool that calculates:

• Fuel blend ratio (example: 9:1)
• Final blended octane rating (AKI)
• Ethanol percentage (E10, E30, E85, etc.)
• Fuel density
• Energy content
• Required mixing volumes
• Suitability for your application (street, track, turbo, drag)

It removes guesswork and replaces it with clear numbers.

If you are blending 93 octane with E85, or adding race fuel to pump gas, this tool shows what you actually get.

Why Fuel Blending Matters

Fuel blending directly affects:

• Knock resistance
• Power output
• Fuel economy
• Air-fuel ratio
• Injector duty cycle
• Fuel system compatibility

For example:

• Higher ethanol increases octane.
• Higher ethanol lowers energy per gallon.
• More octane allows more timing and boost.
• Too much ethanol can cause lean conditions if not tuned.

A proper fuel mixture calculator helps you balance performance and safety.

Understanding the Fuel Options

The calculator includes common fuels used in street and racing applications.

87 AKI Regular (E0)

Standard pump gasoline with no ethanol.
Typical octane: 87 AKI.

Best for daily drivers with low compression.

91 AKI Premium (E0)

Higher octane pump fuel.
Typical octane: 91 AKI.

Common in performance street cars.

93 AKI Premium+ (E0)

High-octane pump gas available in some regions.
Typical octane: 93 AKI.

Often used as a base fuel for ethanol blending.

E85 (Pump, 51–83% Ethanol)

Pump ethanol blend. Ethanol content varies seasonally.

Typical properties:

• Octane: ~105 AKI
• Lower energy than gasoline
• High knock resistance

Ideal for turbo and high boost builds.

Pure Ethanol (E100)

• Octane: ~108.6 AKI
• Very high knock resistance
• Lower energy density than gasoline

Requires full fuel system compatibility.

Pure Methanol

• Octane: ~108.7 AKI
• Very high cooling effect
• Much lower energy content

Common in drag racing applications.

C16 Race Fuel

• Octane: 116 AKI
• Very high energy content
• Designed for extreme boost and compression

Used in professional motorsport.

100LL Avgas

• Octane: 100 AKI
• Aviation gasoline
• Not designed for modern emissions systems

Sometimes used in racing builds, though not recommended for street use.

How the Fuel Percentage Calculator Works

The calculator processes five main inputs:

1. Primary fuel (base)
2. Secondary fuel (additive)
3. Mixture ratio
4. Total mixture volume
5. Target application

Let’s break these down.

1. Primary Fuel (Base)

This is your main fuel. For example:

• 93 AKI pump gas
• E85
• Race fuel

The base fuel provides:

• Base octane
• Density (g/mL)
• Energy content (kJ/kg)

2. Secondary Fuel (Additive)

This is the fuel you add to increase octane or ethanol content.

Examples:

• Adding E85 to 93 octane
• Adding race gas to pump fuel
• Adding methanol

If you choose “None,” the calculator treats it as a single fuel.

3. Mixture Ratio (9:1 Example)

The ratio field determines percentage.

Example:

9 : 1

Total parts = 10

That equals:

• 90% base fuel
• 10% secondary fuel

You can choose:

• Volume ratio (most common)
• Mass/weight ratio (advanced use)

The calculator automatically converts ratio into percentage.

4. Total Mixture Volume

You can enter:

• Gallons (US)
• Liters
• Fluid ounces

If you enter 10 gallons with a 9:1 ratio, the calculator shows exactly how many liters of each fuel you need to pour.

It also calculates total mixture mass.

5. Target Application

This helps the calculator evaluate safety and performance.

Options include:

• Street Daily (87–93 AKI)
• Premium Street (91–95 AKI)
• Track Day (95–100 AKI)
• Drag Racing (100+ AKI)
• High Boost Turbo
• Flex Fuel / E85 conversion

The tool checks if your blended octane meets the minimum requirement.

If not, it gives a warning.

What the Calculator Outputs

Once you click Calculate Mixture, you get:

1. Blended Octane Rating (AKI)

The calculator uses linear blending approximation:

Blend Octane =
(Percentage Base × Base Octane) +
(Percentage Mix × Mix Octane)

Note: Real octane blending is not perfectly linear. Actual results may vary ±2–3 AKI.

2. Ethanol Content (E%)

The calculator estimates ethanol percentage:

• E10
• E30
• E50
• E85
• etc.

This helps determine:

• Fuel system compatibility
• Tuning requirements
• CEL risk in non-flex vehicles

3. Blend Density

Displayed in g/mL.

Important for:

• Injector scaling
• Mass-based tuning calculations

4. Energy Content

Shown in kJ/kg.

This affects:

• Fuel economy
• Required fuel flow
• Injector sizing

Higher ethanol = lower energy per unit volume.

5. Energy Change vs Base

The tool compares blended energy to your base fuel.

Example:

• -5% energy means lower MPG
• +2% energy means slight efficiency gain

6. Octane Status

You’ll see:

• Adequate for application
• Excellent headroom for tuning
• Insufficient for target application

If your blend is too low for turbo or track use, it warns you.

7. Exact Mixing Instructions

If you enter total volume, the tool shows:

• Base fuel in liters
• Secondary fuel in liters
• Total mixture mass

This removes guesswork at the pump.

Example: 93 Octane + E85 Blend

Let’s say:

• Base: 93 AKI
• Mix: E85
• Ratio: 7:3
• Total volume: 10 gallons
• Application: High Boost Turbo

The calculator might output:

• ~99–100 AKI blended
• ~30% ethanol (E30)
• Slight drop in energy vs pure gasoline
• Safe for moderate boost tuning

This is how many tuners create E30 blends for street turbo cars.

Important Technical Notes

1. Octane Blending Is Not Perfectly Linear

The calculator uses linear approximation.

In reality:

• Ethanol can blend non-linearly.
• Real octane may differ slightly.

Treat results as a close estimate, not lab-grade data.

2. Ethanol Affects Fuel Consumption

Higher ethanol:

• Lowers energy density
• Requires more fuel volume
• Reduces MPG

But it:

• Increases knock resistance
• Allows more timing and boost

It’s a trade-off.

3. High Ethanol Requires Compatibility

Blends above E50 may require:

• Ethanol-safe fuel lines
• Larger injectors
• Higher flow fuel pump
• Flex fuel sensor

Always confirm your system supports the blend.

Who Should Use a Fuel Percentage Calculator?

This tool is ideal for:

• Performance car owners
• Turbo and supercharged builds
• Track day drivers
• Drag racers
• DIY tuners
• Flex fuel conversions

If you adjust fuel mixtures even occasionally, this calculator saves time and reduces risk.

Benefits of Using This Calculator

• Accurate percentage breakdown
• Instant octane estimation
• Ethanol content visibility
• Application-based safety checks
• Simple volume instructions
• Clear warnings

It turns a complicated chemical mix into something simple and readable.