Gas Mileage Calculator
Calculate gas mileage (MPG) from odometer readings and fuel fill-up with metric equivalents (km/L, L/100km).
Reviewed by CalculatorApp.me Tools Team
Gas Mileage Calculator — Fuel Economy Guide
Calculate MPG, cost per mile, fuel consumption rates, and compare vehicle efficiency to optimize fuel spending.
25.7 MPG
US avg (2023)
$3.40/gal
US avg regular
~$2,400
Annual fuel cost
15,000 mi
Avg annual miles
Understanding Gas Mileage & Fuel Economy
Gas mileage (fuel economy) measures how efficiently a vehicle converts fuel into distance traveled. In the United States, it's expressed as miles per gallon (MPG) — the higher the number, the more efficient the vehicle. Most other countries use liters per 100 kilometers (L/100 km), where a lower number indicates better efficiency.
The average new car sold in the U.S. in 2023 achieved 25.7 MPG combined (city + highway), according to the EPA. This represents a significant improvement from 20.0 MPG in 2004, driven by federal CAFE (Corporate Average Fuel Economy) standards, turbocharging, direct injection, hybrid drivetrains, and lightweight materials.
The two most important factors affecting your real-world MPG are driving behavior (aggressive acceleration reduces fuel economy by 15-33%) and speed (every 5 mph above 50 mph costs roughly an extra $0.20 per gallon). Tire pressure, vehicle maintenance, AC usage, cargo weight, and weather also significantly impact fuel consumption.
Gas Mileage & Fuel Cost Formulas
MPG = Miles Driven ÷ Gallons Used Example: 350 miles on 14.2 gallons MPG = 350 ÷ 14.2 = 24.6 MPG Combined MPG (EPA method): 1/Combined = 0.55/City + 0.45/Hwy Example: 28 city / 36 highway 1/Combined = 0.55/28 + 0.45/36 = 0.01964 + 0.01250 = 0.03214 Combined = 1 / 0.03214 = 31.1 MPG Note: EPA combined weights 55% city and 45% highway to reflect typical American driving patterns.
Track MPG by recording odometer and gallons at every fill-up. Consistency over multiple tank-fulls gives the most accurate picture.
L/100km = (Liters Used ÷ km) × 100 Convert MPG → L/100km: L/100km = 235.215 ÷ MPG Convert L/100km → MPG: MPG = 235.215 ÷ L/100km Examples: 30 MPG = 235.215 ÷ 30 = 7.84 L/100km 6 L/100km = 235.215 ÷ 6 = 39.2 MPG Imperial (UK) gallons: MPG(UK) = MPG(US) × 1.20095 30 US MPG = 36.0 UK MPG Note: UK gallon = 4.546 L (larger than US gallon = 3.785 L).
When reading European or Canadian fuel economy specs, they use L/100km. UK often uses MPG but with larger imperial gallons — don't confuse with US MPG.
Cost Per Mile ($): = Gas Price ÷ MPG Annual Fuel Cost ($): = (Annual Miles ÷ MPG) × Gas Price Example: 25 MPG, $3.50/gal, 15,000 mi/yr Cost/mile = $3.50 ÷ 25 = $0.14 Annual = (15,000 ÷ 25) × $3.50 = 600 gallons × $3.50 = $2,100 Comparison: 35 MPG vs 25 MPG 35 MPG: 15,000 ÷ 35 = 429 gal = $1,500 25 MPG: 15,000 ÷ 25 = 600 gal = $2,100 Annual savings: $600 (29% less) EV equivalent: 30 kWh/100mi × $0.16 = $0.048/mi vs gasoline at 25 MPG: $0.14/mi
When comparing vehicles, annual fuel cost matters more than MPG. Going from 15 to 20 MPG saves more money than going from 35 to 50 MPG for the same annual miles.
Trip Fuel Cost ($): = (Distance ÷ MPG) × Gas Price Tank Range (miles): = Tank Size × MPG Example: 400-mile road trip, 28 MPG Gallons needed = 400 ÷ 28 = 14.3 Cost at $3.50/gal = $50.00 Tank range: 15-gal tank, 28 MPG Range = 15 × 28 = 420 miles Safe range (leave 10%) = 378 miles Round-trip cost: 800 miles ÷ 28 MPG = 28.6 gallons 28.6 × $3.50 = $100.00 Split between passengers: 4 passengers: $25.00 each vs. flying: ~$200+ per person
Always calculate fuel costs BEFORE road trips. For long trips, compare driving cost (fuel + tolls + wear) vs flying or train — driving is usually cheaper for 2+ passengers.
Fuel Economy by Vehicle Type
| Vehicle Type | City MPG | Highway MPG | Combined MPG | Annual Fuel* |
|---|---|---|---|---|
| Compact sedan | 30–35 | 38–44 | 33–39 | $1,300–$1,550 |
| Midsize sedan | 28–32 | 36–42 | 31–36 | $1,400–$1,650 |
| Full-size sedan | 24–28 | 32–38 | 27–32 | $1,600–$1,900 |
| Compact SUV | 26–30 | 32–38 | 28–33 | $1,550–$1,800 |
| Midsize SUV | 22–26 | 28–34 | 24–29 | $1,750–$2,150 |
| Full-size SUV / truck | 16–20 | 22–28 | 18–23 | $2,200–$2,850 |
| Hybrid sedan | 48–58 | 44–52 | 46–55 | $700–$900 |
| Hybrid SUV | 38–44 | 36–40 | 37–42 | $950–$1,100 |
| Plug-in hybrid | 80–120 MPGe | 35–42 gas | 50–80 actual | $500–$900 |
| EV (no gas) | 100–140 MPGe | 90–120 MPGe | 95–130 MPGe | $450–$700† |
| Diesel truck | 18–22 | 24–30 | 20–25 | $2,000–$2,500 |
| Motorcycle | 40–60 | 50–70 | 45–65 | $700–$1,000 |
*At $3.40/gal, 15,000 mi/year. †EV cost based on $0.16/kWh average. MPGe = miles per gallon equivalent (33.7 kWh = 1 gallon). Ranges reflect 2023-2024 model averages.
Fuel Cost Comparison: Gasoline vs Alternatives
| Fuel Type | Unit Price | Energy / Unit | Cost per 100 mi | Annual Cost* |
|---|---|---|---|---|
| Regular (87 oct) | $3.40/gal | 33.7 kWh/gal | $13.60 (25 MPG) | $2,040 |
| Premium (93 oct) | $4.00/gal | 33.7 kWh/gal | $16.00 (25 MPG) | $2,400 |
| Diesel | $3.80/gal | 37.9 kWh/gal | $15.20 (25 MPG) | $2,280 |
| E85 (Flex fuel) | $2.80/gal | 26.5 kWh/gal | $14.74 (19 MPG) | $2,211 |
| Electricity (home) | $0.16/kWh | 1 kWh | $4.80 (30 kWh) | $720 |
| Electricity (DC fast) | $0.40/kWh | 1 kWh | $12.00 (30 kWh) | $1,800 |
| Hydrogen (FCEV) | $16/kg | 33.3 kWh/kg | $24.24 | $3,636 |
| CNG | $2.50/GGE | 33.7 kWh/GGE | $10.00 (25 MPGGE) | $1,500 |
*Based on 15,000 mi/year. GGE = gasoline gallon equivalent. Prices are US national averages (2024). Actual costs vary by region and vehicle efficiency.
Proven Tips to Improve Gas Mileage
Drive at steady speed
7-14%Use cruise control on highways. Every 5 mph above 50 costs ~$0.20/gallon extra.
Avoid aggressive acceleration
15-33%Gradual acceleration and braking dramatically improve city MPG. Coast to red lights.
Check tire pressure monthly
3-4%Under-inflated tires increase rolling resistance. Every 1 PSI drop costs ~0.2% MPG.
Remove excess weight
1-2% per 100 lbsAn extra 100 lbs in trunk reduces MPG by ~1%. Clean out unnecessary cargo.
Use recommended fuel grade
VariesPremium fuel doesn't help engines designed for regular. Only use premium if required by manufacturer.
Plan and combine trips
Up to 20%Several short cold-start trips use more fuel than one multi-stop trip. Engines are most efficient when warm.
History of Fuel Economy Standards
1908
The Ford Model T gets approximately 13-21 MPG. With gasoline at $0.18/gallon, fuel economy wasn't a concern for early motorists.
1973
The OPEC oil embargo causes gas prices to quadruple overnight. Long lines at gas stations spark national urgency for fuel-efficient vehicles.
1975
Congress passes the Energy Policy and Conservation Act, establishing CAFE (Corporate Average Fuel Economy) standards — requiring automakers to achieve 18 MPG by 1978, rising to 27.5 MPG by 1985.
1993
The EPA introduces the current fuel economy testing procedure, replacing the overly optimistic 1975 test cycle. This results in more realistic (lower) MPG numbers on window stickers.
2007
The Energy Independence and Security Act raises CAFE targets to 35 MPG by 2020. This accelerates development of hybrids, turbo engines, and lightweight materials.
2012–present
Obama-era rules target 54.5 MPG by 2025 (later relaxed to ~40 MPG). EV sales accelerate, reaching 9% of new US car sales in 2023. The EPA introduces MPGe ratings for electric vehicles.
Research & Industry Data
EPA Fuel Economy Guide (fueleconomy.gov)
Official US government source for MPG ratings on every vehicle sold since 1984. Compare vehicles, calculate fuel costs, and find the most efficient models in each class.
Visit EPA Fuel Economy Guide (fueleconomy.gov) →DOE Alternative Fuels Data Center
Comprehensive data on alternative fuel prices, station locations, vehicle availability, and fuel cost comparisons across gasoline, diesel, electricity, hydrogen, and CNG.
Visit DOE Alternative Fuels Data Center →Oak Ridge National Laboratory — Transportation Energy Data Book
The definitive reference for US transportation energy statistics: fleet fuel economy trends, fuel consumption by vehicle type, and historical efficiency data since 1960.
Visit Oak Ridge National Laboratory — Transportation Energy Data Book →ICCT — Real-World Fuel Economy Gap
The International Council on Clean Transportation researches the gap between laboratory fuel economy ratings and real-world driving. Studies show a 25-40% gap in Europe and 10-20% in the US.
Visit ICCT — Real-World Fuel Economy Gap →Common Gas Mileage Myths vs Facts
MYTH
Premium gasoline gives better gas mileage in any car.
FACT
Premium fuel only benefits engines specifically designed for it (high-compression or turbocharged engines that require 91+ octane). In a regular car, premium fuel provides zero MPG improvement — you're just paying 15-20% more per gallon for no benefit.
MYTH
Warming up your car for 5-10 minutes improves fuel economy.
FACT
Modern fuel-injected engines need only 30-60 seconds of idle time even in cold weather. Idling for 10 minutes wastes 0.1-0.2 gallons and produces unnecessary emissions. The fastest way to warm your engine is to drive gently.
MYTH
Manual transmissions always get better gas mileage than automatics.
FACT
This was true decades ago, but modern automatic transmissions with 8-10 speeds and torque converter lock-up often match or exceed manual MPG. CVTs (continuously variable transmissions) in hybrids are among the most efficient.
MYTH
Opening windows is always more fuel-efficient than using AC.
FACT
Below 40-45 MPH, open windows are more efficient. Above that speed, the aerodynamic drag from open windows actually uses MORE energy than the AC compressor. On the highway, use AC; in city driving, open the windows.
MYTH
Smaller cars always get better gas mileage than larger cars.
FACT
Vehicle size is only one factor. A modern midsize turbocharged sedan (35 MPG) can beat a poorly designed compact (28 MPG). Aerodynamics, engine technology, weight, and drivetrain design matter as much or more than overall size.
MYTH
Fuel additives and 'MPG boosters' significantly improve fuel economy.
FACT
The FTC and EPA have tested hundreds of aftermarket MPG-improvement products. None have been proven to improve fuel economy by more than 1-2%. The best 'fuel saver' is gentle driving, proper tire pressure, and regular maintenance.
Frequently Asked Questions
How do I calculate my car's mileage (MPG)?+
Fill your tank completely, note your odometer reading, drive normally until near empty, then refill and note the gallons added. Divide miles driven by gallons used — this calculator does that division for you from your start odometer, end odometer, and gallons filled. For accuracy, average results across at least 3 full tanks.
What is the difference between city and highway MPG?+
City MPG accounts for stop-and-go driving with frequent braking and acceleration. Highway MPG reflects steady-speed cruising. Highway MPG is typically 20-40% higher because constant speed is more fuel-efficient.
How does speed affect gas mileage?+
Most vehicles reach peak fuel efficiency around 35-50 MPH. Above 50 MPH, aerodynamic drag increases sharply. Each 5 MPH increase above 50 costs roughly $0.20 more per gallon — driving 70 vs 55 can reduce MPG by 15-25%.
What is MPGe and how does it apply to EVs?+
MPGe (miles per gallon equivalent) converts electric energy into a gasoline-equivalent figure using 33.7 kWh = 1 gallon. A 100 MPGe EV travels 100 miles on the same energy content as 1 gallon of gas.
Does AC actually hurt gas mileage?+
Yes, AC compressors typically reduce MPG by roughly 5-15% depending on the system and driving conditions. At highway speeds (45+ mph), however, running AC is usually more efficient than driving with open windows due to reduced aerodynamic drag.
How much does tire pressure affect MPG?+
Every 1 PSI drop in tire pressure decreases MPG by roughly 0.2%. Being under-inflated by 10 PSI across all four tires can cost 3-4% MPG. Check tires monthly when cold — pressure drops about 1 PSI per 10°F temperature decrease.
How do I convert between MPG and L/100km?+
Divide 235.215 by the MPG value: 30 MPG = 235.215 ÷ 30 ≈ 7.84 L/100km. To go the other way, divide 235.215 by the L/100km value. This calculator uses that same 235.215 conversion constant for its metric-equivalent result. Note: UK MPG uses imperial gallons (4.546 L), while US MPG (used here) uses US gallons (3.785 L).
Does ethanol (E10, E15, E85) reduce gas mileage?+
Yes. Ethanol contains roughly 33% less energy per gallon than gasoline. E10 (standard US gas) typically reduces MPG by a few percent; E85 (flex fuel) reduces MPG more substantially, though it is also usually priced lower per gallon.
How much can I save by switching to a more efficient car?+
Going from 20 MPG to 30 MPG on 15,000 miles/year saves about 250 gallons annually. Enter your own distance, gallons, and fuel price into the calculator above to see your actual cost per mile and total fuel cost, then compare it against a target vehicle's MPG.
What is hypermiling?+
Hypermiling is a set of driving techniques aimed at maximizing fuel economy: steady speed, gentle acceleration, anticipating traffic, minimizing braking, maintaining tire pressure, and reducing vehicle weight and drag.
Why does my actual MPG differ from the EPA rating?+
EPA ratings come from lab testing under controlled conditions. Real-world factors — aggressive driving, short trips with a cold engine, AC use, cargo weight, hills, wind, rain, and tire condition — typically bring real-world MPG below the sticker value. Tracking your own fill-ups with this calculator gives you your actual, real-world number.
How do I calculate the cost of a road trip?+
Estimate your distance, divide by your MPG to get gallons needed, then multiply by the fuel price per gallon. This calculator's cost-per-mile and total-fuel-cost figures are based on exactly this math, so you can also multiply its cost-per-mile result by any other trip distance to estimate a different route.
References & Sources
- U.S. Environmental Protection Agency & Department of Energy. "Fuel Economy Guide — Model Year 2024." fueleconomy.gov
- U.S. Department of Energy. "Tips to Improve Your Gas Mileage." Office of Energy Efficiency & Renewable Energy. energy.gov
- Oak Ridge National Laboratory. "Transportation Energy Data Book," Edition 42, 2024. tedb.ornl.gov
- NHTSA. "Corporate Average Fuel Economy Standards." National Highway Traffic Safety Administration. nhtsa.gov
- AAA. "Your Driving Costs — 2024 Edition." American Automobile Association. aaa.com
- International Council on Clean Transportation. "From Laboratory to Road: Real-World Fuel Consumption and CO2 Emissions." 2023. theicct.org
Track Your Gas Mileage & Save on Fuel
Calculate MPG, compare fuel costs, and discover proven strategies to improve your vehicle's fuel economy.
Try the Gas Mileage Calculator →Gas Mileage Calculator — Answer & Method
Calculate fuel efficiency in MPG or L/100km and track fuel consumption over time.
Formula: MPG
MPG = Miles Driven / Gallons Used
Example Calculation
350 miles on 12 gallons = 29.17 MPG.
Important limitation
Check the result against your specific circumstances before making a decision.
Key Facts
- The average fuel economy for new US cars in 2025 is about 27.5 MPG.