Gas Cost Calculator – Road Trip Fuel Cost Estimator

Planning a drive? This free gas cost calculator estimates your road trip's fuel cost in the US from the distance in miles, your car's MPG and the current gas price — plus the cost per mile for easy splitting.

How to Use the Gas Cost Calculator

Enter the one-way trip distance in miles — Google Maps gives you this in seconds. Next, enter your car's fuel efficiency in miles per gallon (MPG). If you don't know it, fill the tank, reset your trip odometer, drive normally until the tank is low, then divide the miles driven by the gallons refilled. Finally, enter the current gas price per gallon (the default is $3.50 — update it to today's pump price) and press Calculate Gas Cost.

The result shows four figures: total fuel cost for the trip, gallons of gas needed, cost per mile, and the round-trip cost. The per-mile figure is the most useful of the bunch — it lets you split costs fairly with passengers and compare the running cost of different cars at a glance.

The Formulas

Gallons needed is simply distance divided by MPG — a car that gets 28 MPG needs about 8.6 gallons to cover 240 miles. Multiplying by the price per gallon gives the total cost.

The cost-per-mile formula is the same idea rearranged: each mile consumes 1/MPG gallons, each costing the pump price. At $3.50/gallon and 28 MPG, every mile costs $0.125 — a number that stays constant no matter how far you drive, which is why it's the fairest basis for splitting.

Worked Example: A 240-Mile Road Trip

A weekend road trip of about 240 miles — roughly New York City to Boston. Take a midsize sedan getting 28 MPG with gas at $3.50 per gallon:

Now compare with an SUV getting 20 MPG: 240 ÷ 20 × 3.50 = $42.00 one way — $12.00 more for the same trip. That difference, multiplied over a year of driving, is exactly why MPG matters more than most buyers realize.

How to Cut Your Per-Mile Cost — What Basic Calculators Don't Tell You

The calculator gives you the number; this section helps you shrink it. MPG is not a fixed property of your car — it is a range, and where you sit in the range is mostly driving behavior:

The single biggest lever is speed: aerodynamic drag rises with the square of speed, so cruising at 65 instead of 80 on the interstate can take a 28 MPG car to 32–33 MPG. On the 240-mile example, that alone saves roughly $4.50 per one-way trip. Measure your own MPG honestly (with your normal AC use and load) rather than trusting the EPA sticker figure — sticker numbers are measured in ideal conditions you will never reproduce.

Limitations

This is a fuel-cost estimate, not a full trip budget. Tolls (the Mass Pike alone is a real add-on), food, parking, and wear-and-tear are not included. MPG varies with traffic, road condition, load, tire pressure and driving style — city driving can be 30% worse than highway MPG, so a single figure is always an approximation. Gas prices move frequently, so the default $3.50 is a starting point, not a quote. For a monthly budget, multiply the per-mile cost by your typical monthly miles and add 10–15% as a buffer.

Guides for This Tool

A downloaded route map, a "free" PDF itinerary, a confirmation that will not open — travel files deserve the same suspicion as any download. The Fake File Detector checks what a file really is beneath its extension, right in your browser, before you trust it.

Frequently Asked Questions

Related Tools