ReckonBoxWhat a trip costs in fuel
Fuel cost is the fuel a trip burns, the distance divided by your fuel economy, multiplied by the price. Three numbers you already know turn into the cost before you leave the driveway.
A 300 mile trip in a car that gets 25 MPG needs 12 gallons. At $3.50 a gallon that is $42.00. The arithmetic is not the interesting part. What the tool adds is the cost per mile, $0.14 here, which is the number that lets you compare a route, a car, or a whole month of driving without the distance getting in the way.
Cost per mile is the honest comparison
Cost per mile for fuel is simply the price per gallon divided by your MPG. At $3.50 and 25 MPG it is $0.14 a mile, so 100 miles costs $14 in gas and 12,000 miles a year costs about $1,680.
Total trip cost mixes two things, how far you drove and how thirsty the car is. Cost per mile strips the distance out, so a 25 MPG sedan at $0.14 a mile and a 15 MPG truck at $0.23 a mile compare cleanly no matter whose commute is longer. It is also the figure that scales: multiply it by your annual miles and you have a fuel budget.
| At $3.50 a gallon | Cost per mile | 12,000 miles a year |
|---|---|---|
| 40 MPG | $0.088 | $1,050 |
| 25 MPG | $0.140 | $1,680 |
| 15 MPG | $0.233 | $2,800 |
In litres and kilometres
Switch the units to metric and the whole tool works in petrol terms: kilometres for the distance, km per litre for the economy, and a price per litre in rupees or dollars. The math is the same shape. Litres used is the distance divided by your km per litre, the cost is that times the price per litre, and the cost per kilometre is the price per litre divided by your km per litre.
A 500 km trip at 15 km per litre needs about 33.33 litres. At 100 a litre that is 3,333, and the cost per kilometre is about 6.67. As with miles, the per kilometre figure is the one worth remembering, because it lets you compare two cars or a month of commuting without the distance getting in the way.
Round trips and real economy
A round trip doubles the distance, so it doubles the fuel, and the tool doubles it for you when you pick round trip, so you key in the one-way distance once. The bigger source of error is the economy you feed it. The EPA sticker is measured under controlled conditions, and short hops, cold starts, highway speeds past 60 mph, a loaded roof rack, and a heavy right foot all pull real economy below it. For an honest estimate, use the number your trip computer actually shows on a real drive.
Comparing two cars
Open the more options section, enter a second car's economy, and the tool prices the same trip twice. On the 300 mile default at $3.50 a gallon, a 25 MPG car costs $42.00 and a 15 MPG car costs $70.00, so the thirstier one costs $28.00 more for that single trip.
The gap that counts is the yearly one. That $28.00 works out to $0.09 a mile, and across 12,000 miles it grows to about $1,120 a year, every year you own the car. When you're weighing two cars, or deciding whether a thriftier one pays for itself, the per mile difference times your real annual mileage is the figure to run.
What this does not cover
This is fuel, and only fuel. It does not add tolls, the wear that the IRS captures in its far larger per-mile rate, or the depreciation and maintenance that make the true cost of driving a mile several times the fuel alone. For an electric vehicle the same shape of math applies but the inputs change, cost per kWh and miles per kWh instead of price per gallon and MPG, so this fuel-based tool does not fit an EV cleanly.
Run your real trip computer figure through it once and the annual number is usually higher than the mental estimate.
Frequently asked questions
How do I calculate the fuel cost of a trip? Divide the distance by your MPG for the gallons, then multiply by the price per gallon. A 300 mile trip in a car that gets 25 MPG needs 12 gallons, and at $3.50 a gallon that is $42.00. Dividing the price by the MPG gives the cost per mile, $0.14 here, which is handy for comparing routes or vehicles.
How do I calculate petrol cost in litres and kilometres? Switch the units to metric and the same math runs on kilometres, litres and km per litre. Litres used is the distance divided by your km per litre, times the petrol price per litre for the total. A 500 km trip at 15 km per litre needs 33.33 litres, and at 100 a litre that is 3,333, or about 6.67 per km. Choose rupees or dollars for the currency.
What is the cost per mile or per km to drive? Cost per unit of distance is the fuel price divided by your fuel economy: price per gallon divided by MPG, or price per litre divided by km per litre. At $3.50 a gallon and 25 MPG it is $0.14 a mile, so every 100 miles costs $14 in gas. It is a cleaner number than total trip cost for comparing two cars, because it strips out how far you happen to be going.
How much does gas cost for 1,000 miles? Enter 1,000 as the distance and the tool returns it. At 25 MPG that is 40 gallons, and at $3.50 a gallon it is $140.00, which is the same $0.14 per mile scaled up. Change the MPG or the price and the 1,000 mile figure moves with them, which is why cost per mile is the number worth remembering.
How much does a round trip cost? A round trip doubles the distance, so it doubles the fuel and the cost. The 300 mile example becomes 600 miles, 24 gallons, and $84.00 at $3.50 a gallon. Select round trip and the calculator doubles the distance for you rather than making you enter it twice.
Why is my real MPG lower than the sticker? Because the EPA rating is measured under controlled conditions, and real driving rarely matches them. Short trips, cold starts, highway speeds above 60 mph, roof racks, and hard acceleration all cut fuel economy. For an honest trip estimate, use the MPG your trip computer actually shows rather than the window sticker.
How do I compare the fuel cost of two cars? Open the more options section and enter a second car's economy. The tool then shows both costs and the gap. On the same 300 mile trip at $3.50 a gallon, a 25 MPG car costs $42.00 and a 15 MPG car costs $70.00, so the thirstier car costs $28.00 more, or about $0.09 a mile. Over 12,000 miles a year that gap is about $1,120.