Real math for the garage.
The Grease-Stained Gearhead for the Weekend Wrencher — free calculators for engine builds, drivetrain, fuel systems, wheels and shop work. Just the numbers you actually need.
Browse by category
10 calculators
Engine
Compression, cam timing, displacement & more
5 calculators
Drivetrain
Gear ratios, quarter mile & driveshaft speed
5 calculators
Fuel & Forced Induction
Injectors, carbs, boost & turbo sizing
3 calculators
Wheels & Tires
Tire size, offset & backspacing
10 calculators
Shop & Body
Paint, coating, budget & shop tools
3 finders
Finders
Which paint, media & project fits you?
9 tools
Converters & Lookups
Torque, sockets, taps & lug patterns
Start here
Gear Ratio / RPM / Speed Calculator
Solve for gear ratio, engine RPM, or road speed from any two of the three — the most-searched calculator in the whole auto-enthusiast space.
Tire Size Calculator
Compare tire dimensions, sidewall height, and overall diameter between two sizes before you buy.
Compression Ratio Calculator
Calculate static and dynamic compression ratio — a genuinely underserved search with weak competition online.
Guides
Gear Ratios Explained: Axle, Transmission and Tire Size
How axle, transmission and tire size set rpm, and how to pick gears for towing or the strip.
Reading a Tire Sidewall and Choosing a New Size
Decode the sidewall, work out diameter and speedometer error, and pick a size that fits.
Compression, Cam Timing and Pump Gas: Making the Combination Work
How compression, cam duration, overlap and octane interact, and how to match them.
Sizing an Air Compressor for Your Shop
CFM, PSI, tank size and duty cycle explained, with a method for matching a compressor to your tools.
All GarageCalcs tools
Engine
Cam Timing Calculator Compression Ratio Calculator Coolant Mix Calculator Cylinder Head Flow Horsepower Calculator Displacement Calculator Engine Rebuild Cost Calculator Header Primary Tube Calculator Horsepower and Torque Calculator Piston Speed Calculator Rocker Ratio & Valve Lift CalculatorDrivetrain
Drag Racing Gear Calculator Driveshaft Critical Speed Calculator Gear Ratio Calculator Quarter Mile Calculator Speedometer Gear CalculatorFuel & Forced Induction
Boost Horsepower Calculator Carburetor CFM Calculator Fuel Injector Calculator Fuel Pump Calculator Turbo Pressure Ratio CalculatorShop & Body
Auto Paint Calculator Body Filler & Primer Calculator Brake Pedal Ratio Calculator EV vs Hybrid vs Gas Cost Calculator Powder Coating Calculator Pressure Washer Chemical Dilution Calculator Restoration Budget Calculator Sandblaster Compressor CFM Calculator Wire Gauge Calculator Workshop Heating (BTU) CalculatorNo calculators match your search.
How GarageCalcs works
A garage project is a chain of calculations: how big an engine you are building, what gearing and tires you need, how much paint to buy, what fits your car. GarageCalcs does the arithmetic and explains the method, so you can see how each answer was reached. Each tool says where a figure is an estimate, and your vehicle's service manual always has the last word.
Where to start
- Planning an engine: start with the Engine Displacement and Compression Ratio calculators.
- Changing wheels or gearing: use the Tire Size Converter and the Speedometer Gear Calculator.
- Planning paint work: take the Paint Finish Finder and use the Auto Paint Calculator.
- Choosing a first project: try the Project Car Finder.
Read more about the site, how we calculate and our disclaimer and safety notes. Spotted a mistake? Tell us.