# Trip fuel cost calculator

> Fuel cost of a trip from distance, mpg or L/100 km and fuel price, with tolls, a round-trip option and the cost split per person.

Interactive version: https://www.calcopenly.com/construction/fuel-cost-calculator
Subject: Construction and home calculators

Fuel used is the distance divided by the fuel economy, and fuel cost is that volume times the price per litre or gallon. Tolls and parking are added for each leg, a round trip doubles both the distance and the tolls, and the total is divided by the people sharing the car. Economy can be entered in L/100 km, km/L, US mpg or UK mpg, and the price per litre, US gallon or imperial gallon.

With the defaults, 300 km at 7 L/100 km burns 21 L. At 1.75 a litre that is 36.75 of fuel, and 10 of tolls brings the trip to 46.75, or 23.38 each for two people. The same sum prices a commute, a holiday drive or a share of the petrol money.

The answer is only as good as the economy figure. Speed, traffic, load and cold weather all change consumption, so a figure worked out from your own fill-ups gives a closer cost than the official rating.

## Inputs

- **Distance (one way)**
- **Fuel economy**
- **Fuel price per** (options: Litre, US gallon, UK gallon)
- **Fuel price**
- **Tolls and parking (one way)**
- **Round trip**
- **People sharing the cost**

## Results

- Trip cost — main result
- Cost per person
- Fuel cost
- Fuel used (L)
- Fuel used (US gal)
- Cost per km
- Cost per mile

## Formula

$$
\text{fuel} = \frac{d}{\text{km/L}},\qquad \text{cost} = \text{fuel} \times p + \text{tolls},\qquad \text{per person} = \frac{\text{cost}}{\text{people}}
$$

## Worked examples

### 300 km at 7 L/100 km, 1.75 per litre, 10 in tolls, 2 people

- Distance (one way): 300 km
- Fuel economy: 7 L/100 km
- Fuel price per: Litre
- Fuel price: 1.75
- Tolls and parking (one way): 10
- People sharing the cost: 2
- **Fuel used: 21 L**
- **Fuel cost: 36.75**
- **Trip cost: 46.75**
- **Cost per person: 23.38**
- **Cost per km: 0.16**
- Checked against: Hand calculation: 300 × 7/100 = 21 L × 1.75 = 36.75 + 10 = 46.75; ÷ 2 = 23.375

### 500 mi each way at 30 mpg, $3.50/gal, round trip, 4 people

- Distance (one way): 500 mi
- Fuel economy: 30 mpg (US)
- Fuel price per: US gallon
- Fuel price: 3.5
- Tolls and parking (one way): 0
- Round trip: yes
- People sharing the cost: 4
- **Fuel used: 33.33 US gal**
- **Trip cost: 116.67**
- **Cost per person: 29.17**
- **Cost per mile: 0.12**
- Checked against: Hand calculation: 1,000 mi ÷ 30 mpg = 33.33 gal × 3.50 = 116.67; ÷ 4 = 29.17

### 200 miles at 45 mpg (UK), £1.45 per litre

- Distance (one way): 200 mi
- Fuel economy: 45 mpg (UK)
- Fuel price per: Litre
- Fuel price: 1.45
- Tolls and parking (one way): 0
- People sharing the cost: 1
- **Fuel used: 20.2 L**
- **Trip cost: 29.30**
- Checked against: Python decimal: 200 ÷ 45 × 4.54609 L = 20.2048 L × 1.45 = 29.297

### Edge: round trip doubles the tolls too

- Distance (one way): 100 km
- Fuel economy: 5 L/100 km
- Fuel price per: Litre
- Fuel price: 2
- Tolls and parking (one way): 5
- Round trip: yes
- People sharing the cost: 3
- **Fuel used: 10 L**
- **Trip cost: 30.00**
- **Cost per person: 10.00**
- Checked against: Hand calculation: 200 km × 5/100 = 10 L × 2 = 20, plus 2 × 5 tolls = 30; ÷ 3 = 10

## Questions

### How do you calculate the fuel cost of a trip?

Divide the distance by the fuel economy to get the fuel used, then multiply by the price. 300 km at 7 L/100 km uses 300 × 7 ÷ 100 = 21 L, which costs 36.75 at 1.75 a litre. In US units, 500 miles at 30 mpg uses 16.7 gallons, or $58.33 at $3.50 a gallon. Add tolls and parking, then double everything for a round trip.

### How do you convert mpg to L/100 km?

Divide 235.21 by US mpg, or 282.48 by UK mpg; the same division converts L/100 km back to mpg. The constants follow from the US gallon (231 cubic inches, 3.785411784 L), the imperial gallon (4.54609 L) and the mile (1.609344 km), as listed in NIST SP 811. So 7 L/100 km is 33.6 US mpg or 40.4 UK mpg.

### Why is a UK mpg figure higher than a US one for the same car?

The imperial gallon holds 4.54609 L and the US gallon 3.785 L, so a UK gallon is 20% larger and the same car travels 20% further on it. Multiply UK mpg by 0.8327 to get US mpg: 45 UK mpg is 37.5 US mpg. Reading a UK figure as US mpg understates the fuel used by a sixth.

### How do you split gas money fairly?

Add fuel, tolls and parking and divide by the number of people sharing: the default 46.75 trip is 23.38 each for two. That covers only out-of-pocket costs. To include wear, insurance and depreciation, some drivers charge the IRS standard mileage rate instead, 76 cents a mile for business driving from 1 July 2026 (IR-2026-29); fuel alone at 30 mpg and $3.50 a gallon is 11.7 cents a mile.

### Why does my car use more fuel than its official rating?

Driving style and weather move real consumption away from the label. The US Department of Energy's fueleconomy.gov says aggressive driving can cut gas mileage by 15–30% at highway speeds and 10–40% in stop-and-go traffic, and a petrol car's city mileage is roughly 15% lower at 20 °F (−7 °C) than at 77 °F (25 °C). Economy measured from your own fill-ups gives the closest trip cost.

### How accurate is the trip fuel cost calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “300 km at 7 L/100 km, 1.75 per litre, 10 in tolls, 2 people” is checked against Hand calculation: 300 × 7/100 = 21 L × 1.75 = 36.75 + 10 = 46.75; ÷ 2 = 23.375.

### Where does the method come from?

US DOE / EPA fueleconomy.gov — trip cost calculator; NIST Handbook 44 Appendix C — gallon and litre definitions; NIST SP 811 Appendix B.9 — conversion factors for gallon (US and imperial) and mile.

## Sources

- [US DOE / EPA fueleconomy.gov — trip cost calculator](https://www.fueleconomy.gov/trip/)
- [NIST Handbook 44 Appendix C — gallon and litre definitions](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)
- [NIST SP 811 Appendix B.9 — conversion factors for gallon (US and imperial) and mile](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9)