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Free Automotive Calculators

Precision tools for performance builds — tire sizing, boost math, gear ratios, injector flow, compression ratios, and more. No login, no charge, always free.

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Tire Size & Speedometer Correction
Calculate the actual diameter, circumference, and how changing tire sizes affects your speedometer reading.
Most Popular
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Gear Ratio & RPM Calculator
Find your engine RPM at any speed given your transmission gear, final drive ratio, and tire size.
Performance
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Turbo Boost Pressure Ratio
Convert boost PSI to pressure ratio, or work backwards from a target pressure ratio to required boost.
Forced Induction
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Fuel Injector Size Calculator
Size injectors for a target horsepower goal using BSFC, duty cycle, and number of cylinders.
Fuel System
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Horsepower ↔ Torque
Convert between horsepower and torque at any RPM using the SAE formula used on every dyno sheet.
Dyno Math
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Fuel Cost Calculator
Calculate cost per mile, monthly, and annual fuel spend. Compare premium vs regular for your car.
Daily Driver
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Compression Ratio Calculator
Calculate engine compression ratio from bore, stroke, head gasket thickness, deck clearance, and combustion chamber volume.
Engine Build
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AFR & Lambda Calculator
Convert between air-fuel ratio and lambda (λ) for gasoline, E85, ethanol, and diesel fuels.
Tuning
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About TunerBench

TunerBench is a collection of free precision calculators built for performance car enthusiasts, tuners, and builders. Every formula is sourced from SAE standards, factory service manuals, and established motorsport engineering references.

All calculations run entirely in your browser — no data is sent to any server, no account required. Use them on your phone in the garage or at your desk before a build.

Who These Tools Are For