Automotive Tools

Free automotive and car calculators that run entirely in your browser — tire size comparison, gear ratio and RPM/speed, engine displacement, compression ratio, quarter-mile ET and horsepower, EV charging time, 0-60, power-to-weight, wheel offset, towing and payload, vinyl wrap, tire pressure and lease-vs-buy. No accounts, nothing uploaded.

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Tire Size Comparison Calculator

Compare two tire sizes side by side: diameter, sidewall, circumference, revs per mile and the speedometer error from a plus-size change.

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Gear Ratio, RPM & Speed Calculator

Solve for engine RPM, speed, gear ratio, axle ratio or tire diameter from the other four using the classic RPM = MPH·gear·axle·336 / tire formula.

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Engine Displacement Calculator

Calculate engine displacement in cc, liters and cubic inches from bore, stroke and cylinder count, plus the bore/stroke ratio.

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Compression Ratio Calculator

Work out an engine's static compression ratio from bore, stroke, chamber, head-gasket, deck clearance and piston dish or dome volume.

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Quarter-Mile ET, Trap Speed & HP Calculator

Estimate quarter-mile ET, trap speed or flywheel horsepower from vehicle weight using the Roush/Fox drag-racing formulas.

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EV Charging Time Calculator

Estimate EV charging time from battery size, charge levels and charger power (Level 1/2 or DC fast), plus energy and range added.

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0-60 mph Estimator

Estimate a car's 0-60 mph time from horsepower and weight, or the horsepower needed to hit a target time, by drivetrain.

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Power-to-Weight Ratio Calculator

Work out your car's power-to-weight ratio in W/kg, hp per ton and hp per 1000 lb, with a performance-class read-out.

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Vinyl Wrap Material Calculator

Estimate the square footage, linear feet and yards of vinyl needed to wrap your car, with a waste allowance.

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Car Lease vs Buy Calculator

Compare leasing against financing a car over the lease term: lease total cost, net buying cost and which is cheaper.

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Wheel Offset & Backspacing Calculator

Convert wheel width and offset to backspacing in inches, and compare a new wheel against your old one for fitment.

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Towing & Payload Capacity Calculator

Check payload capacity, remaining payload and max trailer weight against GVWR and GCWR, with pass/fail warnings.

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Tire Pressure Temperature Calculator

See how tire pressure changes with temperature using the ideal gas law, plus the ~1 psi per 10°F rule of thumb.

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Horsepower Calculator

Calculate engine horsepower from torque and RPM, or estimate HP from a quarter-mile trap speed or elapsed time, and back-solve torque from a known HP figure.

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2-Stroke Fuel/Oil Mix Calculator

Work out exactly how much 2-stroke oil to add to your fuel for a target ratio like 32:1, 40:1, or 50:1, with the oil amount shown in both millilitres and fluid ounces.

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Speedometer Error Calculator

See how changing tire size shifts your true speed versus the speedometer reading and how much your odometer drifts, by comparing stock and new overall tire diameters.

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Wheel HP ↔ Crank HP Calculator

Convert between dyno wheel horsepower and crankshaft (flywheel) horsepower using a drivetrain-loss estimate based on your drivetrain layout and transmission type.

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Paint Mix Ratio Calculator

Split a target volume of automotive paint into base, hardener, and reducer parts from a mix ratio like 4:1:1, or scale the whole batch up from a known amount of one component.

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Detailing Dilution Ratio Calculator

Work out how much concentrated car-care product and water to combine for a target dilution ratio or percent in any spray bottle or bucket size.

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Coolant / Antifreeze Mix Calculator

Find the antifreeze-to-water volumes for a target concentration and cooling-system capacity, with freeze and boil protection for ethylene-glycol coolant.

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Fuel Injector Size Calculator

Calculate the fuel-injector flow rate needed for a target horsepower from cylinder count, BSFC and duty cycle, or the max HP a given injector supports.

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Engine RPM & Vehicle Speed Calculator

Find engine RPM at a road speed (or speed at an RPM) from transmission gear ratio, final-drive ratio and tire diameter — e.g. RPM at 70 mph in top gear.

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Octane Blending Calculator

Find the octane of a blend of two fuels, or the volumes of each fuel needed to hit a target octane — pump gas with race fuel, E85 or an octane booster.

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