Automotive calculator glossary: car terms & formulas

Axle Ratio compares how different axle (differential) ratios affect towing torque multiplication, highway cruise RPM, and fuel economy for a tow vehicle.

Battery CCA determines minimum cold cranking amps (CCA) car battery needs based on engine size and climate, and check a candidate battery's rating.

Bolt Pattern calculates wheel's bolt circle diameter (PCD) from the number of lugs and the measured distance between adjacent or straight-across bolt holes.

Boost Horsepower estimates horsepower gain from adding turbo or supercharger boost pressure to a naturally aspirated engine's baseline horsepower.

Brake Fade / Rotor Sizing estimates brake kinetic energy from a stop and compares it to rotor thermal mass to gauge brake-fade risk on track or mountain roads.

BSFC calculates Brake Specific Fuel Consumption (BSFC) from fuel flow rate and horsepower, in lb/hp-hr or g/kWh, to gauge engine efficiency.

Car Lease vs Buy compares leasing vs buying a car over time.

Car Maintenance Cost estimates annual maintenance costs by car age, type, and mileage. See a 5-year forecast and keep vs. buy new comparison.

Car Ownership vs Rideshare compares the true cost of owning a car against going car-free with rideshare, transit, and occasional rentals, and finds break-even trips per month.

Car Payment estimates monthly car payment from price, down payment, trade-in, sales tax, fees, term, and APR, with a full amortization schedule and total interest.

Commute cost calculations evaluate total annual commuting expenses across driving fuel, vehicle depreciation, parking, insurance, mass transit fares, and travel time valuation.

Compression Ratio calculates engine's compression ratio from the swept and clearance volumes, or work back to the volume needed for a target ratio.

Compression Ratio to PSI estimates cranking compression pressure from an engine's static compression ratio.

Coolant Mixture calculates how much antifreeze concentrate and water to mix for a target coolant ratio (e.g. 50/50 or 70/30) and see the resulting freeze protection point.

Cost Per Mile calculates total cost per mile to operate a vehicle from fuel, maintenance, insurance, depreciation, and other costs over annual mileage.

Drag Horsepower calculates horsepower required to overcome aerodynamic drag at a given speed, from a vehicle's drag coefficient (Cd) and frontal area.

Dyno Correction Factor calculates SAE J1349 dyno correction factor from temperature and barometric pressure, then convert observed dyno horsepower to corrected horsepower.

E85 Blend calculates how much E85 and pump gasoline to mix in a tank to reach a target ethanol percentage for flex-fuel tuning.

An engine's static compression ratio from cylinder bore, stroke, and combustion chamber/clearance volume.

Engine Displacement calculates engine displacement from bore, stroke, and cylinder count, in liters, cc, and cubic inches.

Engine Hours to Miles converts engine hours to an equivalent mileage estimate (or back) for equipment, trucks, and boats, using the standard ~25-60 mph equivalency rule.

EV Charging Cost calculates electric vehicle charging cost per mile.

EV Home Charger Install Cost estimates cost to install a Level 2 home EV charger: charger, electrician labor, wiring distance, panel work, and permits, plus any incentives.

EV vs Gas Cost compares the total cost of owning an EV vs a gas car — purchase price, incentives, fuel or charging, maintenance, insurance, and resale value.

Final Drive Ratio calculates vehicle's final drive ratio from the transmission gear ratio and rear axle (differential) ratio, and see its effect on RPM at speed.

Fuel Cost estimates fuel cost for any trip by distance and gas price.

Fuel Injector Size calculates minimum fuel injector size (lb/hr or cc/min) needed for a target horsepower, using BSFC, cylinder count, and a safe maximum duty cycle.

Fuel Pump Sizing calculates minimum fuel pump flow rate (liters per hour) needed to safely support a target horsepower level.

Fuel Savings compares two vehicles or MPG figures to see the annual fuel and cost savings from better gas mileage over driving distance.

Gas vs Electric compares gas vs electric vehicle total cost of ownership.

Gas-Oil Ratio calculates amount of two-stroke oil to mix with gasoline for a target ratio like 32:1, 40:1, or 50:1, for any fuel tank size.

Gear Ratio calculates gear ratio from teeth count, plus vehicle speed at a given RPM and engine RPM at a given speed for tire size and final drive.

Gear Ratio for Speed determines axle gear ratio that puts an engine at a target cruise RPM at a given highway speed, based on tire diameter and transmission overdrive ratio.

GVWR/GCWR calculates vehicle's remaining weight margin against its GVWR (loaded weight) and GCWR (combined weight with trailer) ratings.

Horsepower estimates engine horsepower from vehicle weight and quarter-mile trap speed or elapsed time using the standard drag-racing formulas.

Horsepower to Torque converts horsepower, torque, and RPM.

Idling Fuel Cost calculates how much fuel and money idling wastes over a day, month, or year, from idle time and vehicle's idle fuel consumption rate.

Intercooler Sizing estimates minimum intercooler core volume needed to handle a target horsepower and boost level for a turbocharged engine.

Lease Mileage Overage projects whether you'll go over lease's mileage allowance and estimates the overage fee based on current pace of driving.

Miles Per Year calculates average annual mileage from two odometer readings and the time between them, useful for lease mileage checks and insurance estimates.

MPG calculates vehicle's miles per gallon fuel economy.

Nitrous Jetting calculates nitrous and fuel jet sizes needed for a target horsepower shot from a wet nitrous system, and the resulting fuel-to-nitrous ratio.

Oil Change Interval calculates when next oil change is due, in both miles and months, based on driving habits and oil type.

Payload Capacity calculates vehicle's remaining payload capacity — passengers, cargo, and tongue weight combined — from its GVWR and curb weight.

Plus Sizing determines replacement tire size that matches original overall diameter when upgrading to larger wheels, so speedometer stays accurate.

Power-to-Weight Ratio calculates vehicle's power-to-weight ratio in horsepower per pound and horsepower per ton, and compares it against common performance benchmarks.

Quarter-Mile ET estimates vehicle's quarter-mile elapsed time and trap speed from its horsepower and weight, using the Hale and Fox performance formulas.

Road Trip Fuel Cost calculates total fuel cost for a multi-leg road trip, entering distance and gas price per leg, plus a combined total for the whole trip.

RPM from Speed calculates engine RPM at a given road speed from tire diameter, axle ratio, and gear ratio, or find the RPM for every gear in transmission.

Shift Point RPM calculates optimal shift point RPM between gears to keep an engine in its powerband, from the horsepower curve peak RPM and gear ratios.

Speedometer Error calculates how a different tire size changes true speed and odometer reading versus what the speedometer shows.

Stopping Distance calculates braking distance by speed and conditions.

Tire Diameter calculates tire's overall diameter, circumference, and revolutions per mile from its sidewall size code (e.g. 225/45R17).

Tire Pressure by Temperature calculates how tire pressure changes with ambient temperature using the roughly 1 PSI per 10°F rule, so you can adjust fill pressure for the season.

Tire Rotation Interval calculates how many miles until next tire rotation is due, and when that will happen based on average driving mileage.

Tire Size compares tire sizes and check speedometer accuracy.

Torque to Horsepower converts engine torque (lb-ft) and RPM to horsepower, or horsepower and RPM back to torque, using the standard hp=T×RPM/5252 formula.

Towing Capacity calculates vehicle's maximum safe towing capacity from its GCWR, curb weight, and passenger/cargo load, and check a trailer's weight against it.

Trailer Tongue Weight calculates ideal tongue weight range for a loaded trailer — typically 10-15% of total trailer weight — and check actual tongue weight against it.

Turbo Size estimates compressor airflow (lb/min) a turbocharger needs to support a target horsepower, to help select an appropriately sized turbo.

Two-Stroke Fuel Mix calculates two-stroke fuel-to-oil mix amounts for multiple containers at once, with running totals, for chainsaws, trimmers, and outboard motors.

Used EV Battery Health & Resale Value estimates used EV's remaining battery range and how degradation affects resale value, from model, age, mileage, chemistry, and climate.

Volumetric Efficiency calculates engine's volumetric efficiency (VE%) from displacement, RPM, and actual airflow, to gauge how effectively the engine fills its cylinders.

Wheel Backspacing converts wheel offset (ET, mm) and backspacing (inches), or calculate backspacing directly from wheel width and offset.

Wheel Horsepower converts flywheel (crank) horsepower and wheel horsepower (WHP) using drivetrain loss percentages for manual, automatic, AWD, and CVT transmissions.

Wheel Offset calculates how a wheel offset change shifts the wheel's position in or out of the fender, and the resulting change in track width.

Winch Size calculates minimum rated line pull a winch needs using the standard rule of 1.5x vehicle's fully loaded (GVWR) weight.

0-60 MPH calculates 0-60 mph time from horsepower and weight.