MPG Calculator
Calculate your vehicle's miles per gallon from odometer readings or total miles driven. See your fuel efficiency rating, cost per mile, and metric L/100km equivalent - all updated in real time.
Enter Your Trip Data
📍 Distance
Enter odometer readings or total distance directly. If both odometer fields are filled, the distance is calculated automatically.
⛽ Fuel Used
Results
Average MPG by Vehicle Type
Reference table based on EPA data for model year 2024. Compare your result to your vehicle category.
| Vehicle Type | City MPG | Highway MPG | Combined MPG |
|---|---|---|---|
| Compact Car / Sedan | 30 | 38 | 33 |
| Midsize Sedan | 28 | 36 | 31 |
| Full-size Sedan | 23 | 32 | 27 |
| Small SUV / Crossover | 26 | 32 | 28 |
| Midsize SUV | 22 | 28 | 25 |
| Full-size SUV | 16 | 22 | 18 |
| Pickup Truck | 18 | 24 | 21 |
| Minivan | 22 | 28 | 25 |
| Sports Car | 20 | 28 | 24 |
| Hybrid | 48 | 46 | 47 |
🛠 How to Improve Your Fuel Economy
1. Keep Tires Properly Inflated
Underinflated tires increase rolling resistance and can reduce fuel economy by 3% or more. Check tire pressure monthly when tires are cold. The correct PSI is on the driver's door jamb sticker, not the tire sidewall.
2. Drive Smoothly - Avoid Jackrabbit Starts
Aggressive acceleration and hard braking can lower MPG by 15–30% on the highway and 10–40% in city traffic. Accelerate gently, maintain steady speeds, and coast to red lights instead of braking hard at the last moment.
3. Slow Down on the Highway
Aerodynamic drag increases exponentially with speed. Driving 65 mph instead of 75 mph can improve fuel economy by 10–15%. Use cruise control on flat highways to maintain a consistent speed.
4. Reduce Excess Weight & Drag
Every 100 lbs of extra weight reduces MPG by about 1%. Remove roof racks, cargo carriers, and heavy items you don't need. An empty roof rack alone can decrease fuel economy by up to 5%.
5. Stay on Top of Maintenance
Replace dirty air filters, use the recommended motor oil grade, keep your engine tuned, and fix any check-engine lights promptly. A faulty oxygen sensor alone can reduce MPG by up to 40%.
6. Minimize Idling
Idling gets 0 MPG. If you'll be stopped for more than 60 seconds (not in traffic), turn off the engine. Modern engines use less fuel restarting than idling for extended periods. Use remote start sparingly.
How the MPG Calculator Works
This calculator determines your vehicle's fuel economy using the fundamental relationship between distance traveled and fuel consumed. In the Imperial system used in the United States, fuel economy is expressed as miles per gallon (MPG) - a higher number means better efficiency. The core formula is straightforward:
MPG = Miles Driven ÷ Gallons Used
When you toggle to Metric mode, the calculator accepts kilometers and liters, then computes liters per 100 kilometers (L/100km) - the standard fuel consumption metric used throughout Europe, Australia, Canada, and most of the world. In L/100km, a lower number indicates better efficiency, which is the inverse logic of MPG. The calculator also derives the equivalent MPG so you always have both values side-by-side.
The odometer feature lets you enter starting and ending readings instead of manually computing trip distance. The calculator subtracts start from end and auto-fills the distance field. If you also enter your local fuel price, it computes cost per mile (or cost per kilometer) and total trip fuel cost - critical numbers for fleet operators, rideshare drivers, and anyone tracking vehicle operating expenses.
The efficiency rating classifies your result against EPA fleet averages: below 20 MPG is rated Poor, 20–24 MPG is Fair, 25–29 MPG is Good, and 30+ MPG is Excellent. These thresholds align with the EPA's reported real-world fleet average of approximately 25.4 MPG for model year 2022 light-duty vehicles, as published in the EPA Automotive Trends Report.
The Math Behind It - The 235.214583 Conversion Constant
Converting between MPG and L/100km is not a simple multiplication because the two metrics have an inverse relationship. MPG measures distance per unit of fuel; L/100km measures fuel per unit of distance. The exact conversion uses the constant 235.214583:
L/100km = 235.214583 ÷ MPG
MPG = 235.214583 ÷ L/100km
Where does 235.214583 come from? It is derived from two precisely defined unit conversions established by the National Institute of Standards and Technology (NIST):
- 1 US gallon = 3.785411784 liters (exact, per NIST Handbook 44 and the international yard and pound agreement). The US liquid gallon is defined as exactly 231 cubic inches.
- 1 mile = 1.609344 kilometers (exact, per the 1959 international yard and pound agreement, where 1 yard = 0.9144 meters exactly).
The derivation works as follows. Start with 1 MPG, which means 1 mile traveled on 1 gallon of fuel. To express this in L/100km:
1 mile = 1.609344 km
1 gallon = 3.785411784 L
Fuel rate = 3.785411784 L ÷ 1.609344 km = 2.352145833… L/km
Per 100 km: 2.352145833… × 100 = 235.2145833… L/100km
So a vehicle achieving exactly 1 MPG consumes 235.214583 liters per 100 km. Because the relationship is inverse, dividing this constant by any MPG value yields the L/100km equivalent, and vice versa. This constant is mathematically exact to the precision of the underlying unit definitions and is used universally by engineers, the EPA, and automotive standards bodies.
For km/L (used in Japan, India, and parts of South America), the conversion from MPG is: km/L = MPG × (1.609344 ÷ 3.785411784) = MPG × 0.425143707. Alternatively, km/L = 100 ÷ L/100km.
Industry Standards & References
The U.S. Environmental Protection Agency (EPA) is the federal authority responsible for testing and certifying fuel economy ratings for all passenger vehicles sold in the United States, under 40 CFR Part 600. The EPA uses a five-cycle testing protocol that includes:
- FTP-75 (City): The Federal Test Procedure simulates urban driving - 11 miles over 31 minutes with 23 stops, averaging 21.2 mph, including cold start and hot start phases.
- HWFET (Highway): The Highway Fuel Economy Test covers 10.3 miles at an average speed of 48.3 mph with no stops, simulating free-flow highway driving.
- US06 (High Speed/Aggressive): An 8-mile route with aggressive acceleration, highway speeds up to 80 mph, and rapid speed changes.
- SC03 (A/C): Tests fuel economy with the air conditioning system running at 95°F ambient temperature.
- Cold FTP: The city test repeated at 20°F to account for cold-weather fuel consumption.
The Combined MPG rating on the EPA window sticker is calculated as a weighted harmonic mean of city and highway: Combined = 1 ÷ (0.55/City + 0.45/Highway), reflecting that 55% of typical driving is city and 45% is highway. Note the harmonic mean is used (not the arithmetic mean) because fuel consumption rates, not efficiency rates, are what add linearly.
The European WLTP (Worldwide Harmonized Light Vehicles Test Procedure) replaced the older NEDC cycle in 2017. WLTP results in L/100km tend to be 10–20% higher (worse) than NEDC values because of more realistic test conditions, but they still differ from EPA values. A vehicle rated at 6.0 L/100km on WLTP may test closer to 7.0–7.5 L/100km under EPA methods due to the EPA's more aggressive adjustment factors.
Step-by-Step Example
Scenario: You own a 2023 Honda Civic rated at 33 MPG combined by the EPA. You're comparing it to a European colleague's Volkswagen Golf rated at 5.2 L/100km on the WLTP cycle. After a road trip, you want to calculate your actual fuel economy and see how it compares in metric terms.
Step 1 - Record your data: You filled up at 45,200 miles on the odometer. After driving a mix of city and highway, you filled up again at 45,550 miles. The pump dispensed 12.5 gallons to fill the tank. Fuel price was $3.50/gallon.
Step 2 - Calculate distance:
Distance = 45,550 − 45,200 = 350 miles
Step 3 - Calculate MPG:
MPG = 350 miles ÷ 12.5 gallons = 28.0 MPG
Step 4 - Convert to L/100km:
L/100km = 235.214583 ÷ 28.0 = 8.40 L/100km
Step 5 - Calculate cost per mile:
Total fuel cost = 12.5 gal × $3.50 = $43.75
Cost per mile = $43.75 ÷ 350 = $0.125/mile
Result: Your actual 28.0 MPG is about 15% below the EPA combined rating of 33 MPG - within the typical 10–20% real-world gap. In metric terms, your 8.40 L/100km consumption is significantly higher than your colleague's Golf at 5.2 L/100km (WLTP), though part of that difference is the test-cycle discrepancy. If you convert 5.2 L/100km to MPG: 235.214583 ÷ 5.2 = 45.2 MPG, you can see the Golf is genuinely more efficient - but the gap narrows somewhat when both cars are measured under the same EPA protocol.
Common Mistakes to Avoid
- Not filling the tank completely on both fill-ups: The tank-to-tank method only works if you fill to the same level each time. Topping off to the first click of the pump nozzle at the same station gives the most consistent results. Why it matters: A half-gallon error on 10 gallons used creates a 5% error in your MPG calculation.
- Confusing US gallons with Imperial (UK) gallons: A US gallon is 3.785 liters; an Imperial gallon is 4.546 liters - about 20% larger. UK MPG figures are always higher than US MPG for the same vehicle. This calculator uses US gallons. Why it matters: Using the wrong gallon definition produces a 20% error and makes cross-country comparisons meaningless.
- Averaging MPG values arithmetically: If you got 20 MPG on one tank and 30 MPG on another, your average is not 25 MPG. You must use the harmonic mean or convert to gallons-per-mile first. Over equal distances, the correct average is
2 ÷ (1/20 + 1/30) = 24.0 MPG. Why it matters: The arithmetic mean always overestimates fuel economy because MPG is an inverse measure. The EPA uses the harmonic mean for this reason. - Comparing EPA ratings to WLTP or NEDC ratings directly: Different test cycles produce different numbers. A car rated at 40 MPG by the EPA might be listed as 4.8 L/100km (≈49 MPG) on WLTP. Why it matters: You'll think a vehicle is more or less efficient than it actually is if you compare across different testing standards without adjustment.
- Ignoring ethanol content: E85 (85% ethanol) contains roughly 27% less energy per gallon than pure gasoline. Even standard E10 (10% ethanol) reduces fuel economy by about 3–4% compared to pure gasoline. Why it matters: Switching fuel blends will change your MPG results even if nothing else about your driving or vehicle changes.
When to Use This Calculator
- Tracking real-world fuel economy per fill-up - compare your actual MPG against the EPA window sticker value to spot declining efficiency that may indicate maintenance issues like a failing O2 sensor, clogged fuel injector, or dragging brake caliper.
- Converting between MPG and L/100km - essential when comparing US-market vehicles to European, Australian, or Canadian specifications, importing a vehicle, or reading international automotive reviews.
- Fleet management and expense reporting - calculate cost per mile for mileage reimbursement (the IRS standard mileage rate for 2024 is 67 cents/mile, which includes fuel, depreciation, and maintenance), or verify whether your fleet vehicles are performing within expected efficiency bands.
- Diagnosing fuel economy problems - a sudden drop of more than 10–15% from your established baseline MPG is a reliable early warning of mechanical issues. Track every fill-up to establish your vehicle's normal range across seasons and driving conditions.
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Frequently Asked Questions
How do I calculate my car's MPG?
Fill your tank completely, reset your trip odometer (or note your current mileage), then drive normally until you need fuel again. Fill up completely and note how many gallons it took. Divide the miles driven by the gallons used: MPG = Miles Driven ÷ Gallons Used. For example, if you drove 350 miles and used 12.5 gallons, your MPG is 350 ÷ 12.5 = 28 MPG. For the most accurate result, fill up at the same pump and stop at the first click.
What is a good MPG for a car?
For a gasoline-powered vehicle, 25–30 MPG combined is considered good, and anything above 30 MPG is excellent. Compact cars and hybrids often achieve 35–55+ MPG. Full-size trucks and SUVs typically get 15–22 MPG. The best comparison is against the EPA estimate for your specific vehicle - you can look it up at fueleconomy.gov.
How do I convert MPG to L/100km?
To convert US miles per gallon to liters per 100 kilometers, divide 235.215 by your MPG value: L/100km = 235.215 ÷ MPG. For example, 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. Note that a lower L/100km number means better fuel economy - the opposite of MPG where higher is better. This calculator does the conversion automatically when you toggle to metric.
Why is my actual MPG lower than the EPA estimate?
EPA estimates are measured under controlled lab conditions that don't reflect real-world driving. Factors that reduce your actual MPG include: stop-and-go traffic, cold starts (especially in winter), aggressive acceleration, highway speeds above 60 mph, running A/C, carrying extra weight, underinflated tires, and short trips where the engine never fully warms up. Most drivers get 10–20% less than the EPA combined rating.
Does driving speed affect MPG?
Yes, significantly. Most vehicles reach peak fuel efficiency between 35–55 mph. Above 50 mph, aerodynamic drag increases rapidly with the square of speed. Every 5 mph over 50 is roughly equivalent to paying an extra $0.20–$0.30 per gallon. Driving at 70 mph vs. 55 mph can reduce your fuel economy by 15–25%. Use cruise control on the highway to maintain steady, efficient speeds.
How often should I check my MPG?
Track your MPG every fill-up for the most accurate picture. A sudden drop in fuel economy - more than 10–15% below your normal average - can indicate problems like underinflated tires, a dirty air filter, failing oxygen sensor, dragging brakes, or engine issues. Consistent tracking helps you catch maintenance problems early before they become expensive repairs.