How to Calculate Gas Mileage and Fuel Cost
Gas mileage, measured in miles per gallon (MPG), tells you how efficiently your vehicle uses fuel. Knowing your MPG helps you estimate trip costs, compare vehicles, and budget for fuel expenses. The average American drives about 13,500 miles per year and spends $2,000-$3,500 on gasoline depending on their vehicle's fuel efficiency and gas prices.
Fuel Cost Formulas
Gallons Needed = Distance / MPG
Trip Cost = Gallons Needed x Gas Price
Cost Per Mile = Gas Price / MPG
Where:
Distance = Trip distance in miles
MPG = Your vehicle's fuel efficiency
Gas Price = Current price per gallon of gasoline
Gas Mileage Calculation Example
Given
Distance
300 miles
MPG
28 MPG
Gas Price
$3.50/gallon
Calculation Steps
- 1Gallons needed: 300 miles / 28 MPG = 10.71 gallons
- 2Trip cost: 10.71 gallons x $3.50 = $37.50
- 3Cost per mile: $3.50 / 28 = $0.125 per mile
- 4Annual cost (12,000 miles): 12,000 / 28 x $3.50 = $1,500/year
- 5Monthly fuel cost: $1,500 / 12 = $125/month
Result
A 300-mile trip in a car getting 28 MPG at $3.50/gallon costs $37.50 in fuel (10.71 gallons). Annual fuel cost for 12,000 miles is $1,500.
Annual Fuel Cost by Vehicle Type
| Vehicle Type | Average MPG | Annual Gallons | Annual Cost | Monthly Cost |
|---|---|---|---|---|
| Large SUV/Truck | 18 MPG | 667 | $2,333 | $194 |
| Midsize SUV | 24 MPG | 500 | $1,750 | $146 |
| Midsize Sedan | 30 MPG | 400 | $1,400 | $117 |
| Compact Car | 35 MPG | 343 | $1,200 | $100 |
| Hybrid | 50 MPG | 240 | $840 | $70 |
| Plug-in Hybrid | 70+ MPGe | 171 | $600 | $50 |
| Electric Vehicle | 100+ MPGe | ~$480 electric | $480 | $40 |
How to Calculate Your Actual MPG
Track Your Real MPG
1
Fill Up Completely
Fill your tank to full and note the odometer reading (or reset the trip meter).
2
Drive Normally
Drive until you need to refuel, using your normal driving patterns.
3
Fill Up Again and Record
Fill up completely again. Note the gallons purchased and the new odometer reading.
4
Calculate MPG
Divide miles driven by gallons purchased. Example: 300 miles / 10.5 gallons = 28.6 MPG.
5
Track Over Time
Repeat for 3-5 fill-ups and average the results for a reliable MPG figure.
Tips to Improve Gas Mileage
- Keep tires properly inflated (under-inflation reduces MPG by 0.2% per 1 PSI drop)
- Remove excess weight from the trunk (100 lbs reduces MPG by ~1%)
- Use cruise control on highways (saves 7-14% on fuel)
- Avoid aggressive acceleration and hard braking (can reduce MPG by 15-30%)
- Drive the speed limit (MPG decreases rapidly above 50 mph)
- Keep up with maintenance: clean air filters, fresh oil, tuned engine
- Combine errands into fewer trips (cold starts use more fuel)
- Use the recommended octane grade (premium is not better if your car does not require it)
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Gas vs. Electric Cost Comparison
At $3.50/gallon with a 30 MPG car, driving costs $0.117/mile in fuel. An electric vehicle at $0.14/kWh and 3.5 miles/kWh costs $0.04/mile, about 66% cheaper. For 12,000 annual miles, that is $1,400 for gas vs. $480 for electricity, saving $920/year.
Road Trip Fuel Cost Planner
| Trip Distance | Gallons Needed | Fuel Cost | Fuel Cost (Round Trip) |
|---|---|---|---|
| 50 miles | 1.8 gal | $6.25 | $12.50 |
| 100 miles | 3.6 gal | $12.50 | $25.00 |
| 200 miles | 7.1 gal | $25.00 | $50.00 |
| 300 miles | 10.7 gal | $37.50 | $75.00 |
| 500 miles | 17.9 gal | $62.50 | $125.00 |
| 1,000 miles | 35.7 gal | $125.00 | $250.00 |