Gas Cost Calculator
Estimate how much fuel a trip will cost, in US or metric units. Enter a distance and your vehicle's fuel efficiency to get a cost, or work backward from a recent fill-up (distance driven and fuel used) to find your actual mpg or L/100km.
- Trip Fuel Cost
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- Fuel Needed
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- Fuel Efficiency
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- Cost Per Person
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Rates and figures last updated: July 24, 2026
Assumptions
- Fuel price defaults to the U.S. national average for regular gasoline. Gas prices vary significantly by region and change frequently, so replace the default with your local price for an accurate estimate.
- The metric fuel price default is a direct unit conversion of the same U.S. dollar-per-gallon average, not an independently sourced metric-region price.
- Real-world fuel economy depends heavily on driving style, terrain, vehicle load, tire pressure, and vehicle condition, and typically runs lower than a vehicle's rated or manufacturer-claimed figure, especially in city driving or cold weather.
- When calculating from a fill-up, the distance and fuel amount you enter are assumed to cover exactly one full tank between fill-ups. Partial fill-ups or topping off partway through a tank will skew the calculated efficiency.
- This estimates fuel cost only. It does not include tolls, parking, maintenance, depreciation, or other costs of driving.
Sources
- U.S. Energy Information Administration, Gasoline and Diesel Fuel Update, U.S. Regular Gasoline Prices, accessed July 24, 2026 ($4.001 per gallon as of July 20, 2026).
- U.S. Environmental Protection Agency, Fuel Economy Guide, on typical passenger vehicle fuel economy ratings and how real-world driving affects them.
How trip cost is calculated
Fuel needed is distance divided by fuel efficiency (miles divided by mpg, or litres per 100 km scaled to the actual distance), and cost is that fuel amount multiplied by the price per gallon or litre. The same formula runs in reverse for the fill-up mode: fuel efficiency comes from dividing the distance you drove by the fuel it took to refill, and cost comes from multiplying that same fuel amount by the price you enter.
Why your real mpg might differ from the sticker number
A vehicle's advertised fuel economy rating comes from standardized lab testing, not your actual roads. City driving, stop-and-go traffic, cold starts, highway speeds above about 50 mph, a loaded trunk or roof rack, underinflated tires, and aggressive acceleration all reduce real-world fuel economy, sometimes substantially. Calculating your own mpg from an actual fill-up, using the reverse mode here, gives a more honest number for your specific vehicle and driving conditions than relying on the rated figure alone.
Worked example
A 300-mile trip in a vehicle rated at 25 mpg, with gas at $4.00 per gallon.
Fuel needed = 300 miles / 25 mpg = 12 gallons. Cost = 12 gallons x $4.00 = $48.00 for the trip. Splitting that between, say, 3 people sharing the drive would bring it to $16.00 each.
Frequently asked questions
How does this calculator estimate what a trip will cost in gas?
It divides your trip distance by your vehicle's fuel efficiency to get the fuel needed, then multiplies that by the price per gallon or litre you enter. The default price is the current U.S. national average, but your actual cost depends on local prices, which can vary by more than a dollar a gallon between regions.
Can I use this to estimate gas cost for a multi-day road trip?
Yes. Enter your total planned driving distance for the whole trip, not just one day, and the result gives you total fuel cost across the entire route. If you're sharing the trip with others, enter how many people are splitting the cost to see the per-person amount too.
What if I only know how many miles I drive in a typical week or month?
Enter that mileage as the distance, along with your vehicle's fuel efficiency and local gas price, to get the fuel cost for that period. The math is identical whether the distance represents a single trip, a week of commuting, or any other stretch of driving.
How do I find my cost per mile instead of a trip total?
Divide the trip fuel cost this calculator gives you by the distance you entered. At 25 mpg and $4.00 a gallon, for example, $48.00 over 300 miles works out to 16 cents per mile. This calculator shows the trip total rather than a per-mile figure directly, since per-mile cost is most useful once you already have a total to divide.
How accurate is this gas cost estimate?
It's only as accurate as the fuel efficiency and price you enter. Using your vehicle's actual mpg, calculated from a real fill-up with the 'distance and fuel used' mode, gives a more reliable estimate than relying on the manufacturer's rated figure, since real-world driving conditions typically bring fuel economy down from the sticker number.
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