Miles Per Gallon Calculator

Miles Per Gallon Calculator

About Us

This site is built around one simple mission: help everyday drivers understand their fuel efficiency and make smarter decisions at the pump. Fuel is one of the largest ongoing costs of owning a car, and knowing your miles per gallon can add up to real savings over the life of a vehicle. Our tagline says it best — Calculate Smarter. Drive Further.

We build free, easy-to-use tools that take the guesswork out of fuel math. Whether you want to calculate your miles per gallon, convert between MPG and L/100km, estimate the cost of a road trip, or compare fuel savings between two vehicles — you get fast, reliable answers without sign-ups, paywalls, or clutter. Every calculator is free, on any device.

Accuracy matters. Every calculator on this site is built on well-established formulas — the same ones used by the U.S. Department of Energy (DOE) and the EPA's fuel economy testing program — so you can trust the numbers you get. We also publish practical guides in our blog to help you put those numbers into context — from improving your driving habits to choosing a more efficient vehicle.

This tool is for anyone who drives: commuters watching their monthly fuel budget, families planning long trips, rideshare drivers tracking real costs, and car shoppers comparing efficiency before they buy. Whoever you are — we're here to help you get more out of every gallon.

What We Offer

How We Build and Check Our Calculators

Every tool on this site runs entirely in your browser. Nothing you type is sent to a server, stored, or logged — which is also why we can offer the calculators without an account. The trade-off is that we have to get the maths right the first time, so each calculator is built from published, citable formulas rather than approximations:

  • MPG (US): miles driven ÷ US gallons used.
  • MPG (UK/Imperial): miles driven ÷ Imperial gallons used. One Imperial gallon is 4.54609 L, or 1.20095 US gallons, which is why UK figures always look higher than US figures for the same car.
  • L/100km: 235.215 ÷ MPG (US). We use the full constant rather than the rounded 235 you often see, so conversions round-trip cleanly.
  • km/L: MPG (US) × 1.60934 ÷ 3.78541.
  • CO₂ output: 19.6 lb per US gallon of gasoline, from the EPA figure of 8,887 grams of CO₂ per gallon. Diesel is 10,180 grams, or 22.4 lb.
  • Nautical MPG: speed in knots ÷ gallons per hour, with 1 nautical mile treated as 1.15078 statute miles.

Reference figures are sourced from the US Environmental Protection Agency, the US Department of Energy, and the IRS for mileage reimbursement rates. Where a figure changes annually — the IRS standard mileage rate is the obvious one — we date it on the page so you can tell at a glance whether it is current. The rates built into our mileage reimbursement calculator reflect the IRS rates effective 1 July 2026.

What We Do Not Do

We are deliberately clear about the limits of these tools. Our calculators produce estimates. Real-world fuel economy varies with speed, terrain, payload, tyre pressure, ambient temperature, fuel blend, and how you drive — often by 10–20% against the window-sticker figure. We do not sell vehicles, take affiliate commission on car sales, or rank manufacturers. When we quote a number, we say where it came from.

We also do not ask you to sign up, and we do not store the figures you enter. See our privacy policy for the full detail, and our terms of service for the accuracy disclaimer that applies to every result.

Corrections and Contact

If you spot a formula that looks wrong, a figure that has gone stale, or a calculator that behaves oddly, please tell us — corrections are the fastest way this site gets better. Reach us at hello@milespergalloncalculator.com or through our contact form. We read everything and we do fix things.