Automotive Calculators
Calculate IRS mileage reimbursement, gas mileage, tire size, horsepower, and fuel cost — free, in your browser, no account required.
Page verified • Last updated: August 2026
NumCalcX has 5 automotive calculators for the math that comes up around owning and driving a car — from reimbursing business miles at the current IRS rate to decoding a tire size code. Every calculator below runs entirely client-side: nothing you type is sent to a server, and there's nothing to sign up for. Click any calculator to jump straight in.
Fuel Economy
Mileage Calculator
Calculate a mileage reimbursement or tax deduction using the current IRS standard mileage rate for business, medical, moving, or charitable miles.
→Gas Mileage Calculator
Calculate your vehicle's MPG (miles per gallon) and cost per mile from distance traveled and fuel used.
→Fuel Cost Calculator
Calculate the total fuel cost for a trip from distance, your vehicle's MPG, and the price per gallon.
→Performance & Fit
Tire Size Calculator
Decode a tire size code like 225/45R17 into overall diameter, circumference, and revolutions per mile.
→Horsepower Calculator
Calculate horsepower from torque and RPM using the standard HP = (torque × RPM) / 5252 formula.
→Frequently Asked Questions
Are these automotive calculators free to use?
Yes. Every calculator on NumCalcX runs entirely in your browser — no sign-up, no account, and no data sent to a server.
Which calculator should I use for a business mileage tax deduction?
Use the Mileage Calculator — it applies the current IRS standard mileage rate to your business, medical, moving, or charitable miles.
How do I decode a tire size like 225/45R17?
Use the Tire Size Calculator — it parses the width, aspect ratio, and wheel diameter from the code to give you the tire's overall diameter and circumference.