Driving
How To Calculate A Cost Per Mile
Cost per mile is the number that tells you what driving actually costs, and it is almost always higher than the fuel receipt alone suggests.
Quick Answer
cost per mile = total cost / miles driven
- c
- Cost per mile for the trip
- miles
- Distance driven
- mpg
- Fuel efficiency in miles per gallon
- price
- Fuel price per gallon
- other
- Tolls, parking and wear costs
Divide the miles by the fuel efficiency to get gallons used, multiply by the fuel price, add any other costs, then divide the total by the miles. A 120 mile trip at 32 mpg with 3.50 fuel and 15 of extras comes to 0.2344 per mile.
What Is A Cost Per Mile?
Cost per mile is the total cost of a journey divided by its distance. A hundred and twenty mile trip using 3.75 gallons at 3.50 with fifteen of other costs comes to twenty eight twelve, which is 0.2344 per mile.
Fuel is only part of the picture. Tolls, parking, and the wear that each mile puts on tyres, brakes and oil all belong in the calculation, which is why the per mile figure is usually higher than the fuel receipt suggests.
The fuel component comes from dividing the distance by the efficiency to get gallons, then multiplying by the price. It is worth noticing that efficiency appears in the denominator: improving it from 25 to 32 miles per gallon cuts the fuel cost by more than a fifth.
Because the fuel price is a multiplier on gallons used, both halves matter. A more efficient car on an expensive route can cost more per mile than a thirstier one where fuel is cheap, which is why the comparison is worth doing rather than assuming.
Manufacturer efficiency figures are measured under standardised conditions that are hard to reproduce. Real world figures are typically ten to twenty percent worse, so using the official number makes the cost estimate optimistic.
Adding wear costs turns this from a fuel calculation into a true running cost. Depreciation is the largest single cost of car ownership for most people, and allocating a share of it per mile is what makes the figure realistic.
The reimbursement rate used by many employers and tax authorities is essentially an official cost per mile, intended to cover fuel plus wear. Comparing your own figure against it tells you whether you are being fairly compensated for driving on business.
For a business with a fleet, cost per mile is the metric that decides vehicle choice and route planning. Two vehicles with different purchase prices and efficiencies can be compared directly once both are reduced to a cost per mile.
The calculation is easy to invert. Multiply the cost per mile by the distance to get the total, which is what you need for a quote or an expense claim. Multiply by the annual mileage to get a yearly running cost.
Keep the distance in a single unit. Miles with miles per gallon and price per gallon is consistent; kilometres with miles per gallon is not, and the answer will be wrong by a factor of about 1.6.
Finally, be clear about whether the figure is for one trip or for the vehicle overall. A single trip's cost per mile includes only the costs incurred on that trip, while the vehicle's true cost per mile spreads annual insurance, tax and depreciation across the whole year's mileage.
Formula
cost per mile = total cost / miles
Total cost includes fuel and every other cost attributable to the journey.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| c | Cost per mile | currency per mile | Effective cost of each mile driven. |
| C | Total cost | currency | Fuel plus tolls, parking and wear. |
| m | Miles | miles | Distance driven. |
gallons = miles / miles per gallon
Efficiency is in the denominator, so improving it reduces the fuel used and the cost.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| g | Gallons used | gallons | Fuel consumed on the journey. |
| m | Miles | miles | Distance driven. |
| e | Efficiency | mpg | Miles per gallon for the vehicle. |
fuel cost = gallons x price per gallon
The price multiplies the gallons, so both efficiency and fuel price drive the total.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| F | Fuel cost | currency | Money spent on fuel. |
| g | Gallons used | gallons | Fuel consumed. |
| p | Price | currency per gallon | Cost per gallon. |
How To Calculate A Cost Per Mile
- 1
Measure the distance of the trip
Use the actual route distance, not the straight line between the endpoints. Route planners give a realistic figure that accounts for the roads you will actually drive.
- 2
Look up the vehicle's real world efficiency
Manufacturer figures are optimistic by ten to twenty percent. Use a figure from your own fill ups if you have one, or discount the official number.
- 3
Divide distance by efficiency to get gallons
A hundred and twenty miles at thirty two miles per gallon is 3.75 gallons. Notice that efficiency is in the denominator, so a larger number here means less fuel.
- 4
Multiply by the fuel price
3.75 gallons at 3.50 is 13.125. Fuel prices vary by region and by day, so use the price you actually expect to pay rather than a national average.
- 5
Add other costs and divide by the distance
Fifteen of tolls and parking brings the total to 28.125, which divided by a hundred and twenty miles is 0.2344 per mile. This is the figure to compare between vehicles and routes.
Examples
Example 1: A 120 mile trip at 32 mpg
- Distance
- 120 miles
- Efficiency
- 32 mpg
- Fuel price
- 3.50 per gallon
- Other costs
- 15
| Step | Calculation | Result |
|---|---|---|
| Gallons used | 120 / 32 | 3.75 |
| Fuel cost | 3.75 x 3.5 | 13.125 |
| Cost per mile | 28.125 / 120 | 0.2344 |
Result: The trip costs 28.125 in total, which is 0.2344 per mile once fuel and the 15 of other costs are included.
Example 2: A 300 mile drive in a less efficient vehicle
- Distance
- 300 miles
- Efficiency
- 25 mpg
- Fuel price
- 4.00 per gallon
- Other costs
- 20
| Step | Calculation | Result |
|---|---|---|
| Gallons used | 300 / 25 | 12 |
| Fuel cost | 12 x 4 | 48 |
| Cost per mile | 68 / 300 | 0.2267 |
Result: Despite a higher fuel price, this trip comes in at 0.2267 per mile because the longer distance spreads the fixed costs further.
Example 3: A short 50 mile round trip
- Distance
- 50 miles
- Efficiency
- 40 mpg
- Fuel price
- 3.20 per gallon
- Other costs
- 5
| Step | Calculation | Result |
|---|---|---|
| Gallons used | 50 / 40 | 1.25 |
| Fuel cost | 1.25 x 3.2 | 4 |
| Cost per mile | 9 / 50 | 0.18 |
Result: A short efficient trip comes to 0.18 per mile, but the figure rises quickly when fixed costs are spread over fewer miles.
Calculator
Cost per mile
0.2344
- Fuel cost
- $13.13
- Total trip cost
- $28.13
- Gallons used
- 3.75
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
Prefer a full-width tool? Open the A Cost Per Mile calculator page.
Common Mistakes
Using the manufacturer's efficiency figure
Official figures are measured under ideal conditions and are typically ten to twenty percent better than real world driving. Using them makes the cost estimate too low.
Leaving out non fuel costs
Tolls, parking and the wear each mile puts on tyres and brakes are real costs. Counting only fuel understates the true cost per mile, sometimes by half.
Mixing miles with litres
Miles per gallon only works with miles and gallons. Using kilometres with miles per gallon, or litres with a per gallon price, gives an answer out by a factor of several.
Dividing by gallons instead of miles
The formula is total cost over distance. Inverting it gives miles per unit of currency, which is a different and much less useful number.
Forgetting that efficiency is in the denominator
Improving efficiency lowers the gallons used and therefore the cost. Treating it as a multiplier makes a more efficient car look more expensive.
Comparing trips of different lengths
A long trip spreads fixed costs over more miles and therefore has a lower cost per mile. Comparing a short trip against a long one is not a like for like comparison.
Ignoring depreciation in a full running cost
For vehicle ownership rather than a single trip, depreciation is usually the largest cost. A per mile figure that excludes it is a fuel cost, not a running cost.
FAQ
How do you calculate cost per mile?
Divide the distance by the fuel efficiency to get gallons, multiply by the fuel price, add other costs, then divide the total by the distance. A 120 mile trip at 32 mpg with 3.50 fuel and 15 of extras is 0.2344 per mile.
What costs should be included?
At minimum fuel and tolls. For a true running cost, add parking, tyres, servicing and a share of depreciation, which for most owners is the single largest component.
Why is my cost per mile higher than the fuel receipt suggests?
Because fuel is only part of what a mile costs. Wear on tyres and brakes, and the fall in the vehicle's value, happen whether or not you notice them at the pump.
Does a longer trip cost less per mile?
Usually yes, because fixed costs such as tolls and parking are spread over more miles. The fuel component per mile stays roughly constant, so the total falls only if fixed costs do not rise proportionally.
How does efficiency affect the cost?
It sits in the denominator, so improving miles per gallon reduces the gallons used and the fuel cost. Going from 25 to 32 miles per gallon cuts fuel cost by more than a fifth.
Can I use this for kilometres?
Yes, if you convert consistently. Use litres per hundred kilometres and a price per litre, then divide by kilometres. Mixing miles with litres will give a wrong answer.
References
- [1]Wikipedia, Fuel economy in automobiles — https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles
- [2]Wikipedia, Cost per mile — https://en.wikipedia.org/wiki/Cost_per_mile
- [3]Wikipedia, Vehicle depreciation — https://en.wikipedia.org/wiki/Depreciation#Vehicles
- [4]Wikipedia, Miles per gallon — https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles#Miles_per_gallon