Free Automotive Calculators

Professional-grade tools for mechanics, techs, and gearheads. Accurate enough for the shop, simple enough for the driveway. No sign-ups, no BS.

Popular Tools

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Tire Size Comparison

Compare two tire sizes side-by-side. See diameter, width, sidewall, circumference, revs/mile differences, and speedometer correction.

Free Tool

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Fuel Cost Calculator

Calculate trip fuel cost from distance, MPG, and fuel price. Supports round trips, imperial & metric units, and cost-per-mile breakdown.

Free Tool

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MPG Calculator

Calculate miles per gallon from distance and fuel used. Shows L/100km, cost per mile, efficiency rating, and fuel-saving tips.

Free Tool

Browse by Category

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Tires & Wheels

Compare tire sizes, calculate speedometer correction, check wheel offset, bolt patterns, and tire pressure by load.

1 Tool

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Fuel & Cost

Calculate trip fuel costs, MPG, gas vs. diesel vs. EV total cost of ownership, cost per mile, and annual fuel expenses.

2 Tools

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Engine & Performance

Horsepower, displacement, compression ratio, air-fuel ratio, turbo boost, fuel injector sizing, and more.

Coming Soon

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Drivetrain

Gear ratios, final drive, RPM to speed, axle ratios, clutch torque capacity, and driveshaft speed calculators.

Coming Soon

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Shop & Repair

Torque conversion, bolt specs, brake rotor thickness, coolant mix ratios, battery CCA, wiring gauge, and towing capacity.

Coming Soon

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Fabrication

Tube bending, weld filler metal, metal weight, spring rates, and roll cage tube sizing calculators.

Coming Soon

Built for the Shop Floor

WrenchRig is a collection of free automotive calculators built for people who actually work on cars. Whether you're a professional technician, a shade tree mechanic, or a weekend warrior swapping tires in the driveway — these tools are designed to give you accurate answers fast.

Every calculator uses real engineering formulas and industry standards. Big buttons for gloved hands. Imperial and metric units. No accounts, no paywalls, no ads blocking your results. Just tools that work.