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

🛞

Tire Size Comparison

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

Free Tool
⛽

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
📊

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
🏎️

Speedometer Correction

Calculate actual speed vs. indicated speed after changing tire sizes. See exactly how much your speedometer is off.

Free Tool
⚙️

Gear Ratio Calculator

Calculate overall drive ratio, RPM at speed, and theoretical top speed from transmission gear, axle ratio, and tire size.

Free Tool
🔩

Torque Conversion

Convert between ft-lbs, in-lbs, Nm, and kg-cm instantly. Includes common automotive torque specs reference table.

Free Tool
🔧

Engine Displacement

Calculate engine displacement from bore, stroke, and cylinder count. Shows results in cc, cubic inches, and liters simultaneously.

Free Tool
🌡️

Coolant Mix Ratio

Calculate water/coolant ratios for your target freeze point. Supports ethylene and propylene glycol coolant types.

Free Tool
🎯

Wheel Offset Calculator

Calculate offset, backspacing, and track width changes. Compare stock vs new wheel fitment with visual diagrams.

Free Tool
💰

Cost Per Mile

Calculate total vehicle operating cost per mile including fuel, insurance, maintenance, and depreciation.

Free Tool
🐎

HP ↔ Torque Converter

Convert between horsepower and torque at any RPM. Supports HP, kW, PS, ft-lbs, and Nm with instant results.

Free Tool
🔩

Compression Ratio Calculator

Calculate engine compression ratio from bore, stroke, chamber volume, gasket specs, and deck clearance. Includes common engine presets.

Free Tool
🏎️

0-60 & Quarter Mile Calculator

Estimate 0-60 mph time, quarter mile ET, and trap speed from vehicle weight and horsepower. Includes vehicle presets and drivetrain adjustments.

Free Tool
🌡️

Tire Pressure Temperature

Calculate how tire pressure changes with temperature using Gay-Lussac's Law. Find the right cold-set PSI for your target hot pressure.

Free Tool
🔘

Bolt Pattern / PCD Calculator

Calculate your wheel's Pitch Circle Diameter from bolt measurements. Includes vehicle lookup table and standard pattern matching.

Free Tool
🛢️

Oil Mix Ratio (2-Stroke)

Calculate exact 2-stroke oil amounts for any gas/fuel mix ratio. Supports 50:1, 40:1, 32:1 and custom ratios in gallons or liters.

Free Tool
⚙️

Transmission Gear Speed Calculator

Calculate engine RPM and redline speed in up to six gears with transmission presets, final drive, and tire size.

Free Tool
📐

Automotive Alignment Calculator

Convert toe between degrees and linear measurements, then calculate cross camber and cross caster.

Free Tool
⚙️

Wheel Torque Calculator

Estimate total wheel torque after gearing and drivetrain loss, plus optional tractive force at the tire contact patch.

Free Tool

More Calculators

⚙️

Regear Calculator

Find the axle gear ratio needed after a tire-size change and compare nearby available ratios.

Free Tool
↪️

Turning Radius & Turning Circle

Calculate turning radius, turning circle diameter, swept path, and trailer offtracking.

Free Tool
🛞

Revs Per Mile Calculator

Calculate tire revolutions per mile, then compare two sizes for speedometer accuracy.

Free Tool
🏁

Drag Racing ET & Horsepower

Estimate elapsed time, trap speed, or horsepower from vehicle weight and performance data.

Free Tool

Browse by Category

🛞

Tires & Wheels

Compare tire sizes, correct a speedometer, check wheel offset and bolt patterns, and calculate tire pressure and fitment.

11 Tools
⛽

Fuel & Cost

Calculate trip fuel cost, fuel economy, and total operating cost per mile.

3 Tools
🔧

Engine & Performance

Calculate displacement, compression ratio, air-fuel ratio, horsepower and torque, and drag-strip performance.

8 Tools
⚙️

Drivetrain

Calculate gear ratios, axle changes, engine RPM at speed, transmission gear speed, and wheel torque.

7 Tools
🔩

Shop & Repair

Convert torque, estimate bolt torque, mix coolant or two-stroke oil, check towing capacity, and plan brake service.

8 Tools
📐

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.