Automotive
Automotive tools are free online calculators for engine and driving math — find displacement, compression ratio, horsepower, fuel cost, tire size, gear ratio and MPG in seconds.
Estimate alternator replacement cost from parts and labor. Enter the alternator price, labor hours and shop rate for an instant total and low-to-high range.
Estimate brake pad and rotor replacement cost from parts and labor. Enter pad sets, rotors, prices, labor hours and shop rate for an itemized total.
Free compression ratio calculator finds your engine's static CR from swept and clearance volume in cc. Get an X.XX : 1 result instantly, with worked examples.
Free engine displacement calculator finds total cc, litres and cubic inches from bore, stroke and cylinders. Works in mm or inches, with worked examples and a size chart.
Free fuel cost calculator works out trip gas cost from distance, MPG or L/100km and fuel price. Get total cost and cost per mile, with worked examples.
Estimate fuel injector replacement cost from parts and labor. Enter how many injectors, price each, labor hours and shop rate for an instant itemized total.
Estimate fuel filter replacement cost from parts and labor. Enter the filter price, labor hours and shop rate for an instant total and a low-to-high range.
Estimate fuel pump replacement cost from parts and labor. Enter the pump price, labor hours and shop rate for an instant total and a low-to-high range.
Estimate fuel cost for a road trip. Enter distance, your car's MPG, and gas price to get total gallons, cost, and the cost split per person, instantly.
Free gear ratio calculator finds gear ratio from driven and driving teeth, then output RPM from input speed. Includes the formula, worked examples and a ratio chart.
Free horsepower calculator finds HP from torque and RPM using HP = torque × RPM ÷ 5252. Convert torque to horsepower instantly, with worked examples and a chart.
Free MPG calculator finds miles per gallon from miles driven and gallons used: MPG = miles ÷ gallons, with L/100km and km/L equivalents and worked examples.
Calculate your car or bike's power-to-weight ratio from horsepower and weight. Get hp/lb, hp/ton and kW/kg instantly with the formula and worked steps shown.
Estimate timing belt replacement cost from parts and labor. Enter parts price, labor hours and shop rate for an instant low-to-high total with the math shown.
Calculate how tire pressure changes with temperature using the gas law. Enter your PSI and the temperature change to see the new pressure. Free, with the formula shown.
Free tire size calculator turns a 225/45R17-style size into sidewall height, overall diameter, circumference and revolutions per mile, with worked examples and a size chart.
Decode any tire size like 225/45R17 into sidewall height, overall diameter, circumference and revolutions per mile. See exactly what the numbers on your tire mean.
Check if your cargo fits a truck by weight and volume. Enter payload, cargo space and item size to see total weight, space used and whether the load fits.
Estimate water pump replacement cost from parts and labor. Enter the pump price, labor hours and shop rate for an instant total and a low-to-high range.
What are automotive tools?
Automotive tools are free online calculators that handle the everyday math of cars and engines: how big an engine is, how hard it squeezes, how much power it makes, what your tires and gearing do, and what driving costs to fuel. Engine builders, tuners, restorers, racers, students and ordinary owners use them to plan a rebuild, spec parts, read a dyno sheet, size wheels, or budget fuel without working the algebra by hand.
Automotive tools on Toolzent
Here are the automotive calculators currently available, each with worked examples on its page.
| Tool | What it does |
|---|---|
| Engine Displacement Calculator | Finds total displacement in cc, litres and cubic inches from bore, stroke and cylinder count, in mm or inches. |
| Compression Ratio Calculator | Returns the static compression ratio as X.XX to 1 from a cylinder’s swept and clearance volume in cc. |
| Horsepower Calculator | Converts between horsepower, torque (lb-ft) and engine speed (RPM); enter any two to solve for the third. |
| Fuel Cost Calculator | Estimates the fuel cost of a trip or commute from distance, fuel economy and price per unit of fuel. |
| Tire Size Calculator | Decodes a tire’s width, aspect ratio and rim size into overall diameter, and compares two sizes for fitment. |
| Gear Ratio Calculator | Works out gear and final drive ratios, plus engine RPM at a given road speed for a chosen gearing. |
| MPG Calculator | Calculates miles per gallon (fuel economy) from the distance driven and the fuel used. |
Key automotive formulas at a glance
These are the equations behind several of the calculators above, with the units each one expects. Keep them nearby when checking your own working.
| Quantity | Formula | Units |
|---|---|---|
| Displacement | (pi/4) x bore squared x stroke x cylinders | mm or inches in; cc, L, ci out |
| Compression ratio | (swept + clearance) / clearance | both volumes in cc; ratio unitless |
| Horsepower | torque x RPM / 5252 | lb-ft, RPM, hp |
| Fuel economy (MPG) | miles driven / gallons used | miles, gallons, MPG |
| Trip fuel cost | distance x price / MPG | miles, price per gallon, total cost |
A few results exactly as the tools return them: an 86 mm bore, 86 mm stroke, 4-cylinder engine gives about 1998 cc, which is 2.0 L and 121.9 cubic inches. A cylinder with 500 cc swept and 50 cc clearance volume gives a static 11.00 to 1 compression ratio. And 400 lb-ft at 5000 RPM works out to 380.8 hp, since horsepower and torque always read equal at 5252 RPM.
How do I choose the right tool?
Match the tool to the number you need to find:
- Working out engine size, or converting cc to cubic inches: use the Engine Displacement Calculator with bore, stroke and cylinder count.
- Speccing pistons, a head gasket or how much to mill a head: use the Compression Ratio Calculator with your per-cylinder swept and clearance volumes.
- Estimating output from a dyno torque reading, or finding the torque a power goal demands: use the Horsepower Calculator and solve for whichever value is missing.
- Budgeting a road trip or daily commute: use the Fuel Cost Calculator, and find your economy first with the MPG Calculator.
- Fitting bigger wheels or checking speedometer error: use the Tire Size Calculator to compare overall diameter.
- Choosing a differential or reading cruising RPM: use the Gear Ratio Calculator.
These pair up naturally: size the engine, set the squeeze, estimate power, then dial in gearing, tires and running cost.
Why use Toolzent’s automotive tools?
Every automotive calculator is 100% free with no sign-up and nothing to install. The tools run privately in your browser, so the bore, volume, torque, mileage and price figures you type stay on your device and results appear instantly. Each page is mobile-friendly, so you can use it in the garage from a phone or tablet, and each documents its formula plus worked examples, so you can both get an answer and verify it. The engine results are clean theoretical figures from ideal geometry, so treat displacement and compression ratio as accurate nominal specs and measure the actual engine for a precise build.
For related calculations, explore our Math & Algebra, Unit Converters and Finance & Investing category hubs.
Frequently asked questions
Are these automotive calculators free to use?+
Yes. Every automotive tool on Toolzent is 100% free, with no sign-up, no download and no usage limits.
How do I calculate engine displacement from bore and stroke?+
Use displacement = (pi/4) x bore squared x stroke x cylinders. An 86 mm bore, 86 mm stroke, 4-cylinder engine works out to about 1998 cc, or 2.0 L and 121.9 cubic inches.
How do I find horsepower from torque and RPM?+
Multiply torque in pound-feet by RPM, then divide by 5252. At 400 lb-ft and 5000 RPM, HP = 400 x 5000 / 5252 = 380.8 hp.
What does a gear ratio tell me about my car?+
It is the ratio of driven to drive gear teeth (or final drive ratio). A higher number means stronger acceleration and more RPM at a given speed; a lower number means relaxed, fuel-efficient cruising.
How do I work out MPG and fuel cost for a trip?+
MPG = miles driven / gallons used. For trip cost, multiply distance by price per gallon and divide by MPG, so 300 miles at 30 MPG and 4.00 dollars per gallon costs about 40.00 dollars.
Do these tools work in both metric and imperial units?+
Most do. The displacement tool accepts mm or inches and reports cc, litres and cubic inches, while fuel and economy tools support common distance, volume and currency choices.