How to Estimate Gas Cost for a Road Trip (With Examples)
Gas is usually the easiest road trip cost to predict, because it comes down to three numbers you can look up before you leave: how far you are driving, how many miles your vehicle gets per gallon, and what gas costs.
The formula
Gallons = miles ÷ MPG
Cost = gallons × price per gallon
That is all the calculator does. Everything else in this guide is about getting those three inputs right.
Step 1: get the real distance
Use the driving distance from a maps app, not the straight-line distance, and decide whether you are pricing one way or the round trip. Then add a margin. Detours, driving around at your destination and missed exits add up; 5% to 10% extra is a reasonable allowance on a long trip.
Step 2: use the right MPG
Your vehicle has more than one fuel economy figure.
- Highway MPG fits long stretches at steady speed.
- Combined MPG fits a mix of highway and town driving.
- Your own measured MPG is the best of all: divide the miles driven on a tank by the gallons it took to refill.
Expect lower fuel economy than the sticker figure if the car is fully loaded, you carry a roof box or bikes, you tow, or you drive fast. You can look up official figures for any make and model on fueleconomy.gov.
Step 3: pick a gas price
Prices differ between states and even between exits. Check prices along your route rather than at home, and use a figure toward the higher end so the estimate does not come up short. The examples here use $3.25 a gallon as a round illustration, not as a current average.
Worked example
A 600-mile round trip in a car that gets 28 MPG, with gas at $3.25:
- Gallons: 600 ÷ 28 = 21.4 gallons
- Cost: 21.4 × $3.25 ≈ $69.64 (using the unrounded gallons)
- Split between 3 people: $23.21 each
Quick reference: gallons and cost by distance
| Miles (one way) | 20 MPG | 25 MPG | 30 MPG | 40 MPG |
|---|---|---|---|---|
| 25 | 1.3 gal, $4.06 | 1 gal, $3.25 | 0.8 gal, $2.71 | 0.6 gal, $2.03 |
| 50 | 2.5 gal, $8.13 | 2 gal, $6.50 | 1.7 gal, $5.42 | 1.3 gal, $4.06 |
| 100 | 5 gal, $16.25 | 4 gal, $13.00 | 3.3 gal, $10.83 | 2.5 gal, $8.13 |
| 250 | 12.5 gal, $40.63 | 10 gal, $32.50 | 8.3 gal, $27.08 | 6.3 gal, $20.31 |
| 500 | 25 gal, $81.25 | 20 gal, $65.00 | 16.7 gal, $54.17 | 12.5 gal, $40.63 |
| 1,000 | 50 gal, $162.50 | 40 gal, $130.00 | 33.3 gal, $108.33 | 25 gal, $81.25 |
Costs are at $3.25 a gallon. For a different price, multiply the gallons by your price.
Think in cost per mile
Dividing the gas price by your MPG gives a cost per mile you can apply to any trip.
| Fuel economy | $3.00 / gal | $3.50 / gal | $4.00 / gal |
|---|---|---|---|
| 15 MPG | 20¢ | 23.3¢ | 26.7¢ |
| 20 MPG | 15¢ | 17.5¢ | 20¢ |
| 25 MPG | 12¢ | 14¢ | 16¢ |
| 30 MPG | 10¢ | 11.7¢ | 13.3¢ |
| 35 MPG | 8.6¢ | 10¢ | 11.4¢ |
| 40 MPG | 7.5¢ | 8.8¢ | 10¢ |
| 50 MPG | 6¢ | 7¢ | 8¢ |
At 25 MPG and $3.50 a gallon, every 100 miles costs $14.00.
Splitting gas fairly
The simplest method is to divide the total fuel cost equally among everyone in the car, driver included. If one person is supplying the car, some groups have the passengers cover all of the gas instead, since the owner is absorbing wear, tires and oil. Agree on the method before the trip rather than at the pump.
What gas money does not cover
Fuel is only part of the cost of driving. Tolls, parking, and wear on the vehicle are separate, and on a long trip they can be significant. If you are comparing driving with flying or taking a train, include them.
Sources
- U.S. Department of Energy and EPA: fueleconomy.gov
- U.S. Energy Information Administration: gasoline and diesel fuel update
This article is general information, not tax, legal or financial advice. See our disclaimer.