Enrichment · Passion Projects · Cars and travel

What one tank says
about a year of driving.

Type the distance and the fuel from one fill-up. The calculator gives the economy both ways, the cost per mile, and what a year of driving costs in fuel, money and carbon dioxide, then sets it against any other car.

Work out the economyWhat you get

The fuel economy calculator

The worked example is made up: one tank in a family hatchback. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
Miles per gallon, litres per 100 km, cost per mile or km, a year’s fuel, cost and carbon dioxide, and the difference against another vehicle. It prints as a summary and downloads as a spreadsheet.
Who it is for
New drivers and families, students comparing cars, math and physics students practising rates and units, and anyone tracking fuel costs.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard, in US or metric units. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Choose miles and gallons or kilometres and litres, and the fuel.
  2. Type the distance and the fuel from one fill-up.
  3. Add the price and a year’s driving for the yearly figures.
  4. Type another vehicle’s rating to compare.
  5. Print the summary or download the spreadsheet.

Work out the economy

How the numbers work

A rate, a unit change and a year.

The worked example: a family hatchbackDistance ÷ fuel29.0 mpg342 mi ÷ 11.8 galFuel a year414 gal12,000 ÷ 29.0Cost a year$1,362414 gal × $3.29CO₂ a year3.68 t414 × 8.887 kgThe worked example: a family hatchbackDistance ÷ fuel29.0 mpg342 mi ÷ 11.8 galFuel a year414 gal12,000 ÷ 29.0Cost a year$1,362414 gal × $3.29CO₂ a year3.68 t414 × 8.887 kg
One fill-up gives the economy; the year’s distance turns it into fuel, money and carbon dioxide.

The conversions

Miles per gallon is distance per fuel; litres per 100 km is fuel per distance, so one is the other turned upside down: L/100 km = 235.215 ÷ mpg, using the exact definitions of the US gallon and the mile. Carbon dioxide comes from the carbon in the fuel: the EPA uses 8,887 grams per gallon of gasoline and 10,180 grams per gallon of diesel.

The mpg illusion

Because mpg is upside down, equal mpg gains are not equal savings. Swapping a 10 mpg truck for a 20 mpg one saves 500 gallons over 10,000 miles; swapping a 25 mpg car for a 50 mpg one saves only 200. When choosing between vehicles, compare fuel per distance, or the fuel a year this page shows.

Sources

  1. U.S. Environmental Protection Agency. Greenhouse gas emissions from a typical passenger vehicle (epa.gov).
  2. U.S. Department of Energy and EPA. FuelEconomy.gov: how to calculate fuel economy and compare vehicles (fueleconomy.gov).
  3. National Institute of Standards and Technology. Special Publication 811, Guide for the Use of the International System of Units, appendix B conversion factors (nist.gov).
  4. Larrick, R. P., and Soll, J. B. (2008). The MPG illusion. Science, 320(5883), 1593–1594.

The worked example is made up. Real-world economy varies with speed, weather and load. Your figures stay in this browser. Support: team@caveatacademic.com.