Fuel Cost Calculator

The formula

• litres_used = distance_km ÷ 100 × L_per_100km
• total_cost = litres_used × price_per_litre
• cost_per_km = total_cost ÷ distance_km
• round_trip_cost = one_way_cost × 2

A worked example

500 km at 8 L/100 km with fuel at $1.20/L: 500 ÷ 100 × 8 = 40 litres; 40 × $1.20 = $48.00 total, or $0.096 per km.

More about the Fuel Cost Calculator

MPG or L/100 km, both work, and here is the difference

L/100 km tells you consumption (lower is better); mpg tells you efficiency (higher is better). They are reciprocals with a unit twist, and mixing them up is the classic error, 8 L/100 km is about 29 mpg, not 8 mpg.

Enter efficiency exactly as your car reports it. If your dashboard shows mpg and your trip is in miles, use miles throughout; if it shows L/100 km, use kilometres. The tool converts internally and keeps every result in the units you chose.

The worked example, step by step

500 km at 8 L/100 km with fuel at $1.20/L: first the fuel, 500 ÷ 100 × 8 = 40 litres. Then the money, 40 × $1.20 = $48.00 total, or $0.096 per km. Flip the round trip toggle and everything doubles: 80 litres, $96.

The imperial version: 500 miles at 30 mpg needs 500 ÷ 30 = 16.7 gallons; at $3.50 a gallon that is about $58. Same arithmetic, different units.

How accurate is the number, really

As accurate as your inputs. Your car's official efficiency figure was measured in a lab; real driving adds traffic, hills, air conditioning, roof boxes and a heavy right foot. Highway cruising usually beats the official figure; stop start city driving usually does not.

For a conservative budget, add 10 to 15% to the fuel figure, or better, use your car's actual long term average from the trip computer instead of the brochure number. And remember tolls, which this calculator does not include: add them under transport in the Trip Budget Calculator for the full picture.

Cutting the fuel bill

The big wins are unglamorous: steady moderate speed (fuel use climbs steeply past ~110 km/h), properly inflated tyres, no roof box unless you need it, and combining errands into fewer trips. Air conditioning costs less than open windows at highway speed, but less than both is just driving smoothly.

For the drive vs fly decision, compare this fuel figure plus tolls against the flight price plus airport transport. Under ~500 km, driving usually wins on cost; beyond that, flying often wins on everything except the scenery.

Why your dashboard lies (a little)

Trip computers are usually optimistic by 5 to 10%. They measure fuel flow, not pump receipts. The honest number is manual: fill the tank, reset the trip odometer, drive normally, refill, and divide litres by kilometres. Do it three times and average.

Use that real world figure here instead of the dashboard's. Your budget will thank you, and you will finally know whether the 'eco' mode actually does anything.

Splitting fuel costs fairly

For road trips with friends, the per km figure is your friend: total fuel cost divided by passengers is the fair split, since everyone benefits equally from the drive. Tolls and parking split the same way.

Do not split by 'who drove most', the driver already paid in attention and fatigue. Equal shares of fuel, tolls and parking is the standard, and the calculator's total makes the math take ten seconds.

Fuel price apps and timing

Fuel prices vary more than people think, 10 to 20% between stations in the same city is common. A fuel price app checked before a long drive routinely saves more than any driving technique.

Fill up before leaving rather than on the motorway, where prices peak. And if your route crosses a border or a state line, check prices on both sides, the difference can be worth a small detour. The calculator tells you the cost; the app tells you where to pay less of it.

Electric vehicles: the fuel cost parallel

EV drivers do the same math with kilowatt hours: (battery size × electricity rate) ÷ range = cost per mile. At $0.15/kWh and 3.5 mi/kWh, that is about 4 cents a mile, roughly a quarter of petrol costs.

Public fast charging costs 2 to 4x home rates, so the 'fuel' math depends heavily on where you charge. Road tripping on fast chargers narrows the gap with petrol significantly.

If you are comparing EV vs. petrol for a purchase decision, run both calculations above with your actual mileage and local prices, the answer is personal, not universal.

The formula, and why cost per mile is the number that matters

The whole calculation is three steps: miles per month divided by MPG gives gallons burned; gallons times the pump price gives the monthly cost; and the pump price divided by MPG gives your cost per mile. That last number is the quiet star of the show. It turns every driving decision into simple arithmetic.

Cost per mile makes comparisons effortless. A car that costs $0.14 a mile to fuel versus one at $0.10 saves $480 a year over 12,000 miles. Delivery and rideshare drivers live by this figure because it decides whether a job actually pays after fuel; car shoppers should too, because two cars with similar sticker prices can differ by thousands in running costs over a few years.

If a single trip is the question rather than the whole month, our Fuel Cost Calculator prices individual journeys with round trip mode and per passenger splits.

MPG or L/100 km, gallons or litres, enter what you know

MPG and L/100 km measure the same thing from opposite ends: MPG is distance per unit of fuel (higher is better), L/100 km is fuel per unit of distance (lower is better). Mixing them up is the classic error, 8 L/100 km is roughly 29 mpg, not 8 mpg.

Enter efficiency exactly as your car reports it and pick the matching fuel price unit: per gallon with mpg, per litre with L/100 km. The calculator converts internally (235.214 ÷ mpg = L/100 km) and reports fuel used in both litres and gallons, so the result reads correctly wherever you are.

Diesel drivers: the arithmetic is identical, just enter the diesel price and your car's diesel efficiency. Diesel usually returns better mileage but costs more per litre, so let the monthly total settle the petrol vs diesel debate rather than the efficiency figure alone.

From a monthly number to a monthly budget

A number is not a budget until it has a home. Slot your monthly fuel cost into your transport category and set the budget 10 to 15% above your real figure, fuel prices swing with crude markets and seasons, and one price spike should not break the plan.

The 50/30/20 Budget Calculator is a good next step: it shows where your fuel line sits inside a full monthly budget and whether transport is quietly eating the savings category. Revisit the fuel number quarterly, or whenever your commute changes, a new job across town can move this figure more than any driving tip.

Cutting the monthly fuel bill

The big wins are unglamorous and free: combine errands into fewer, fuller trips; keep tyres at the manufacturer's pressure (under inflation alone can cost 2 to 3% in fuel); remove the roof box and excess weight; and drive at a steady moderate speed, since fuel use climbs steeply at high speeds. Smooth acceleration beats every gadget ever sold for this purpose.

When shopping for the next car, run two scenarios here before you fall in love: a 35 mpg car costs about 30% less to fuel than a 25 mpg one on the same commute. That gap dwarfs most feature packages over five years of ownership.

You will find this tool alongside the rest of our Car & Auto calculators, including the Car Loan vs Lease Calculator, which answers the bigger question of what the car itself costs you each month, not just the fuel.

When your driving mixes city streets and highway

Most commutes mix city streets and highway, and averaging the two MPG figures directly gives the wrong answer. Suppose 70 of your weekly 100 miles are highway miles at 35 mpg and 30 are city miles at 25 mpg. The highway miles burn 2 gallons, the city miles 1.2, 3.2 gallons total, an effective 31.25 mpg.

The simple average of 35 and 25 is 30 mpg, predicting 3.33 gallons, an overestimate, because gallons add up while MPG figures do not average cleanly. Better to measure: record the odometer, keep a month of receipts, and divide miles by gallons. That figure already contains your real mix, traffic and driving style.

What a more efficient car actually saves, in dollars

Suppose you drive 900 miles a month with petrol at $3.80 a gallon. A 25 mpg car burns 36 gallons, costing $136.80 a month, $1,641.60 a year, and 15.2 cents a mile in fuel alone. A 40 mpg car burns 22.5 gallons, costing $85.50, saving $51.30 a month, or $615.60 a year.

That yearly saving is the honest yardstick for a pricier efficient model. A $1,200 premium is repaid by fuel alone in about 23 months; a $4,000 premium takes past six years, so the decision must then rest on other grounds, reliability, comfort or resale value, rather than fuel.

Mistakes that quietly wreck the estimate

The sneakiest error is building a monthly figure from one week multiplied by four. Months average 4.33 weeks, so the shortcut understates a weekly pattern by roughly 8 percent. Multiply by 52 and divide by 12 instead, or read the odometer twice, one month apart, and use the difference.

The second mistake is entering a fuel price from memory. A 20 cent error on 36 gallons is $7.20 a month, and it compounds into the yearly total and cost per mile. Use the average of your last few receipts, or the price at the station you use most, refreshed whenever prices move.

How to use the Fuel Cost Calculator

1. Enter the trip distance in km or miles.
2. Enter your car's fuel efficiency (L/100 km or mpg).
3. Enter the fuel price per litre (or gallon).
4. Read the fuel used, cost per km and total trip cost, toggle round trip if needed.