Tank-to-tank trip math
You drive 287 miles on 14.2 gallons at fill-up: 287 ÷ 14.2 ≈ 20.2 MPG. That real trip figure is what many owners trust more than a single EPA combined number on the window sticker.
Fuel
MPG Calculator
Calculate true miles per gallon from trip distance and fuel used, plus L/100km and km/L conversions for international drivers. Track tank-to-tank to spot a fueling problem early.
What this calculator is for
An MPG calculator turns miles driven and gallons pumped into real fuel economy, and converts between US MPG, liters per 100 km, and km/L. Window-sticker EPA numbers are a lab benchmark; tank-to-tank math is what your wallet feels.
Commuters log winter vs summer tanks; road-trippers check whether a roof box killed highway economy; importers compare US MPG to European L/100 km listings.
A good outcome: one honest MPG number you can plug into the fuel cost calculator for trip budgeting.
Calculator
How to use this calculator
- From trip — divide miles driven by gallons pumped (full fill to full fill is most accurate).
- Convert MPG — enter a known MPG to see L/100 km and km/L.
Fill the tank to the same stop each time (same pump click) for accurate gallons.
Short trips and winter idling destroy MPG — do not judge a car on one cold commute tank.
OBD trip computers are handy but can be 3–5% optimistic vs pump math.
If you only partially fill, you cannot calculate that segment accurately — wait for a full tank.
The math: do it without a calculator
MPG = Miles ÷ Gallons
L/100 km = 235.215 ÷ MPG
km/L = MPG × 0.425144
Example: 300 miles on 12.5 gal → MPG = 300 ÷ 12.5 = 24.0 MPG → L/100 km ≈ 9.8.
MPG = Miles ÷ Gallons. L/100 km = 235.215 ÷ MPG. km/L = MPG × 0.425144.
Example: 287 miles ÷ 14.2 gal ≈ 20.2 MPG → about 11.6 L/100 km.
EPA combined on fueleconomy.gov is useful for comparison, but your driving mix, speed, and load determine real results.
Real-world examples
EPA combined vs. your log
The U.S. EPA publishes city/highway/combined fuel economy labels at fueleconomy.gov. A vehicle labeled 28 mpg combined may log 24–26 mpg in winter idling or towing — tracking gallons pumped over a full tank is the standard way to measure real MPG.
Troubleshooting & fine-tuning your setup
Why Your Real MPG Beats or Misses the Calculator
Tank-to-tank MPG swings with short trips, winter idle, roof racks, and tire pressure. A single partial fill skews gallons used. Fill to the same click, divide miles by gallons, and log several tanks before judging a mod.
EPA combined on the window sticker is a lab cycle — many drivers see lower in city winter and higher on long highway cruises. OBD trip computers can drift 3–5% from pump math.
Frequently asked questions
MPG & Fuel Economy FAQs
How do I calculate real-world MPG accurately?
Reset trip odometer at a full fill, drive your normal mix, fill again, then miles ÷ gallons pumped. Do not trust the dash alone for one tank.
Why is winter MPG worse?
Cold dense air, longer warm-up enrichment, thicker fluids, and winter blend fuel all reduce MPG. Short trips hurt hybrids and turbo cars especially.
How do I convert MPG to L/100 km?
Use L/100 km = 235.215 ÷ MPG (US gallons). Lower L/100 km is better economy, opposite of MPG scale.
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