Automotive Calculators
Decode a tire size, check the speedometer error from a new set of wheels, work out road speed from RPM, size an engine or convert fuel economy between MPG and L/100km. Every tool is exact geometry or a definitional conversion — no estimates — and runs entirely in your browser.
- Tire Size Calculator Enter a tire size like 225/45R17 and get its true measurements
- Tire Size Comparison & Speedometer Error Compare your current and a new tire size to see the diameter difference and exactly how much your speedometer will read off after the change.
- Gear Ratio & RPM Calculator Enter your gear ratio, final drive
- Engine Displacement Calculator Enter the bore, stroke and number of cylinders to get the engine’s displacement in litres, cubic centimetres and cubic inches.
- Compression Ratio Calculator Enter the swept volume and the clearance
- Horsepower & Torque Calculator Convert between horsepower and torque at any engine speed
- Fuel Economy Converter (MPG, L/100km) Convert fuel economy between US MPG, UK MPG, litres per 100 km and kilometres per litre
- Wheel Offset & Backspacing Calculator Convert between wheel offset
- EV Charging Time Calculator Enter your battery size, the charge levels and the charger power to estimate the charging time and energy added.
- Power-to-Weight Ratio Calculator Enter power
- Stopping Distance Calculator Enter your speed, reaction time and the tyre–road grip to get the reaction, braking and total stopping distances.
- Quarter-Mile ET & Trap Speed Calculator Enter horsepower and weight to estimate the 1/4-mile elapsed time and trap speed.
- Fuel Cost Calculator Enter your trip distance, fuel economy and fuel price to see what the fuel will cost.
- Fuel Range Calculator Enter your tank capacity and fuel economy to see how far a full tank will take you.
- Tire Pressure Temperature Calculator Enter your set pressure and the temperature when you set it versus now to see the current pressure.
Frequently asked questions
Are these automotive calculators accurate?
Yes — every one uses exact geometry or a definitional unit conversion, not estimates. Tire dimensions come from the standard code formula, horsepower uses the exact HP = torque × RPM ÷ 5252 relationship, and fuel-economy conversions use the precise US and imperial gallon definitions. They’re Node-tested.
Do they handle metric and imperial units?
Yes. Tire sizes mix millimetres and inches (as the standard does); the displacement tool takes mm or inches; and the fuel-economy converter covers US MPG, UK MPG, L/100km and km/L — correctly accounting for the different US and UK gallons.
Is my data uploaded?
No. Every tool runs entirely in your browser — nothing is sent to a server, and they work offline.
Can I use these for modifications and fitment?
They’re a solid starting point for tire, gearing and wheel-fitment maths. Always verify clearances and manufacturer specifications on your actual vehicle before making changes.