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MPG Calculator
Calculate your vehicle actual miles per gallon (MPG) from odometer readings and fuel fill-up data. Track whether your MPG matches the EPA rating, find how driving habits affect fuel efficiency, and compare gas vs electric vehicle efficiency.
Your vehicle real-world MPG often differs from the EPA sticker rating by 10-20%. City driving, aggressive acceleration, highway speeds, cold weather, and carrying extra weight all reduce fuel economy. Calculating your actual MPG regularly helps identify when maintenance is needed and shows the true cost of your driving habits.
Formula
MPG = Miles Driven / Gallons Used | Miles Driven = Ending Odometer - Starting Odometer | L/100km = 235.215 / MPG
How to Calculate Your Real MPG
To accurately measure your MPG: fill your tank completely, record the odometer reading, drive normally, fill up completely again, record the new odometer reading and gallons pumped. MPG = (New Odometer - Old Odometer) / Gallons Pumped. Repeat 3-5 times for an accurate average, as one tank can vary significantly.
EPA MPG vs Real-World MPG
Condition
MPG Impact
Reason
City driving
15-20% below EPA
Stop-and-go traffic, frequent idling
Highway driving
0-10% below EPA
Most efficient but affected by speed
Combined
10-15% below EPA
Mix of city and highway
Hot weather
2-3% below EPA
AC compressor load
Cold weather
15-25% below EPA
Cold engine, thicker oil, battery drain
AC use
5-25% less
Significant at low speeds
What Hurts Fuel Economy the Most
Ranked by impact: aggressive driving (speeding, rapid acceleration, hard braking) — up to 40% reduction. Excessive speed above 55 mph — 2% per mph over 50. Cold engine warm-up — short trips under 5 miles get terrible MPG. Underinflated tires — 0.2% per PSI. Excess cargo — 1% per 100 lbs. Roof racks and cargo boxes — 2-8% reduction.
Improving Your MPG
Most impactful actions: smooth acceleration and deceleration, maintain steady speed with cruise control, reduce highway speed by 5-10 mph, eliminate unnecessary cargo and roof racks, keep tires properly inflated, get regular tune-ups (especially air filter replacement), use the manufacturer recommended oil grade, and park in shade or garage to reduce AC cooling load.
Frequently Asked Questions
MPG = Miles Driven / Gallons of Fuel Used. Fill up completely, reset trip odometer (or note mileage). Drive normally. Fill up completely again — note miles driven and gallons pumped. MPG = miles / gallons. Example: drove 320 miles, pumped 11.5 gallons = 320/11.5 = 27.8 MPG.
EPA ratings are measured under controlled laboratory conditions. Real-world factors that reduce MPG: city driving vs highway, cold weather (15-25% reduction), aggressive driving (up to 40% reduction), air conditioning (5-25%), high altitude, carrying heavy loads, and vehicle age/maintenance condition. The EPA revised ratings in 2008 to be more realistic, but gaps remain.
Good MPG by vehicle type (2024): Compact car: 35-45 MPG (combined). Midsize sedan: 28-38 MPG. SUV: 22-32 MPG. Pickup truck: 18-25 MPG. Hybrid: 45-60 MPG. Plug-in hybrid: 40-55 MPG gas mode. Electric vehicle: 100-150 MPGe. Any vehicle achieving 35+ combined MPG is considered fuel efficient.
City MPG: measured in stop-and-go traffic with frequent idling and acceleration — typically 20-30% lower than highway. Highway MPG: measured at steady 48-60 mph — engines are most efficient at steady speed. Combined MPG: 55% city + 45% highway weighting. Most drivers experience MPG closer to the combined rating for typical mixed driving.
L/100km = 235.215 / MPG. At 30 MPG: 235.215/30 = 7.84 L/100km. At 40 MPG: 5.88 L/100km. For UK MPG (Imperial gallon): L/100km = 282.481 / UK MPG. The relationship is inverse — higher MPG = lower L/100km (both mean more fuel efficient).
Below 20 MPG combined is considered poor fuel economy for a passenger vehicle. Most full-size SUVs and pickup trucks fall in the 15-20 MPG range. Sports cars with large V8 engines can dip below 15 MPG. For comparison, the US fleet fuel economy standard (CAFE) requires an average of 49 MPG by 2026.