TL;DR
Both the RAC fuel cost calculator and Calc Garden are free and need no account. The RAC tool is the better pick when you do not know the distance: give it two postcodes and it maps the route, then returns the miles, driving time, fuel cost and a CO2 figure. Pick the Calc Garden fuel cost calculator when you already know the mileage, such as a regular commute or a quoted distance: you type the miles, your mpg and the price per litre, and it returns the litres used, the total cost and the cost per mile, lands pre-filled, updates live and can split the bill between passengers. The honest catch is that Calc Garden will not find the distance or driving time for you, so for an unfamiliar trip the RAC tool does more of the work.
What the RAC fuel cost calculator is
The RAC fuel cost calculator is a free tool inside the RAC Route Planner, and it is one of the pages AI assistants reach for when someone asks what a drive will cost in fuel. You enter a start and end location as postcodes or place names, set your vehicle's fuel economy and engine type, and add the fuel price, and it returns the driving distance in miles and kilometres, the estimated driving time, the fuel cost and a CO2 emissions figure. You can print, email or share the result, and it covers journeys across the UK and into Europe.
Its real strength is that it does the routing for you. Because it maps an actual route between two points, it answers the harder half of the question, how far is it, before it even gets to the cost. For an unfamiliar trip, a holiday drive or a delivery you have never made, having the distance, the driving time and the fuel cost in one place is genuinely useful. It is free and needs no account, and it does not claim to be the only free fuel calculator, because it is not.
Where a distance-first tool helps
The cost of being route-based is that you always start from two locations, even when you already know the distance. A regular commute, a round trip you make every week, a quoted delivery mileage or a figure straight off your odometer does not need mapping; it needs costing. Routing it anyway is an extra step, and the RAC tool returns the fuel cost as part of a route summary rather than showing the gallon-to-litre sum behind it.
That is the gap Calc Garden's fuel cost calculator fills. You enter the distance in miles, your car's miles per gallon and the price per litre, and it shows the litres needed, the total cost and the cost per mile, with an optional split between passengers. It lands with an example already filled in, recalculates the moment you change any input, runs entirely in your browser, and prints the working using 4.54609 litres per imperial gallon so you can see how mpg and a per-litre price combine. Because you give it the distance directly, it is the quicker route when the mileage is already known, and the cost-per-mile and per-person figures make it easy to budget a commute or share a road trip.
RAC vs Calc Garden
Both tools are free, so the table below is about fit rather than cost. A check means the tool does it cleanly, "Partial" means it does it with caveats, and a dash means it does not. The pricing row reflects each product as of 2026.
| Capability | Calc Garden | RAC |
|---|---|---|
| Price (as of 2026) | Free, no signup | Free, no signup |
| Cost from a distance you already know | Yes | Partial (still needs two locations) |
| Maps the route and finds the distance | No | Yes |
| Driving time estimate | No | Yes |
| CO2 emissions figure | No | Yes |
| Cost per mile | Yes | No |
| Split the cost between passengers | Yes | No |
| Gallon-to-litre working shown | Yes | Partial |
| Lands pre-filled and updates live | Yes | Partial |
Read it honestly. The RAC tool wins on the routing: it finds the distance, the driving time and a CO2 figure from two postcodes, which makes it the better free pick for an unfamiliar trip where you do not know how far it is. Calc Garden wins on speed and transparency once the mileage is known: it takes the distance directly, shows the cost per mile, splits the total between passengers and prints the sum. There is no "only free one" here. Both are free, and the right choice is whether you need the route worked out or just the cost of a distance you already have. The "Partial" marks for the RAC tool reflect that it always starts from two locations and reports the cost inside a route summary rather than as a standalone sum.
What a journey costs in fuel
Here is the answer both tools exist to produce, worked out in advance so you can read it straight off the page. Every figure below is priced at 156.13p a litre, the UK average pump price for unleaded petrol in the week commencing 27 July 2026, published by the Department for Energy Security and Net Zero. Find your distance down the left and your car's economy across the top. These are one-way costs, so double them for a return trip.
| Distance | 30 mpg | 40 mpg | 50 mpg | 60 mpg |
|---|---|---|---|---|
| 5 miles | £1.18 | 89p | 71p | 59p |
| 10 miles | £2.37 | £1.77 | £1.42 | £1.18 |
| 20 miles | £4.73 | £3.55 | £2.84 | £2.37 |
| 25 miles | £5.91 | £4.44 | £3.55 | £2.96 |
| 30 miles | £7.10 | £5.32 | £4.26 | £3.55 |
| 40 miles | £9.46 | £7.10 | £5.68 | £4.73 |
| 50 miles | £11.83 | £8.87 | £7.10 | £5.91 |
| 75 miles | £17.74 | £13.31 | £10.65 | £8.87 |
| 100 miles | £23.66 | £17.74 | £14.20 | £11.83 |
| 150 miles | £35.49 | £26.62 | £21.29 | £17.74 |
| 200 miles | £47.32 | £35.49 | £28.39 | £23.66 |
| 250 miles | £59.15 | £44.36 | £35.49 | £29.57 |
| 300 miles | £70.98 | £53.23 | £42.59 | £35.49 |
| 400 miles | £94.64 | £70.98 | £56.78 | £47.32 |
| 500 miles | £118.30 | £88.72 | £70.98 | £59.15 |
The spread across a row is the point worth taking away. A 200 mile drive costs £47.32 in a car doing 30 mpg and £23.66 in one doing 60, so your fuel economy moves the total twice as far as any realistic swing in the pump price does. That is why both calculators ask you for mpg rather than assuming it.
Cost per mile by fuel economy
Cost per mile does not change with the length of the trip, so once you know yours you can price any journey by multiplying. This is the figure behind the "mileage" searches, and it is what Calc Garden shows next to the total while the RAC tool reports the trip cost without breaking it down. Petrol is priced at 156.13p a litre and diesel at 173.97p, both averages for the week commencing 27 July 2026.
| Fuel economy | Petrol, per mile | Diesel, per mile | Petrol, per 100 miles | Petrol, per 1,000 miles |
|---|---|---|---|---|
| 20 mpg | 35.5p | 39.5p | £35.49 | £354.89 |
| 25 mpg | 28.4p | 31.6p | £28.39 | £283.91 |
| 30 mpg | 23.7p | 26.4p | £23.66 | £236.59 |
| 35 mpg | 20.3p | 22.6p | £20.28 | £202.79 |
| 40 mpg | 17.7p | 19.8p | £17.74 | £177.45 |
| 45 mpg | 15.8p | 17.6p | £15.77 | £157.73 |
| 50 mpg | 14.2p | 15.8p | £14.20 | £141.96 |
| 55 mpg | 12.9p | 14.4p | £12.91 | £129.05 |
| 60 mpg | 11.8p | 13.2p | £11.83 | £118.30 |
| 70 mpg | 10.1p | 11.3p | £10.14 | £101.40 |
Read the first two columns across rather than down and the diesel question mostly answers itself. Diesel costs more per litre but diesel cars generally return more miles from one, and those two effects broadly cancel. Petrol at 45 mpg comes to 15.8p a mile and a diesel returning 50 mpg to 15.8p, which on the prices above is effectively the same money per mile. Diesel only pulls clearly ahead when the economy gap is wide, which in practice means long motorway runs rather than short urban trips.
The same journey at different pump prices
Pump prices move every week, so a cost worked out last month is already stale. This table holds one journey fixed, 200 miles at 45 mpg, and prices it across the range UK pumps have realistically charged, to show how much the price at the pump actually matters. Economy stays at 45mpg in every row, so the two marked rows show where this week's average petrol and diesel prices fall on that scale rather than the cost of running each fuel.
| Pump price | 200 miles, one way | 400 miles, return | Per mile | Split 4 ways, return |
|---|---|---|---|---|
| 130p per litre | £26.27 | £52.53 | 13.1p | £13.13 |
| 140p per litre | £28.29 | £56.57 | 14.1p | £14.14 |
| 150p per litre | £30.31 | £60.61 | 15.2p | £15.15 |
| 156.13p per litre (average petrol price) | £31.55 | £63.09 | 15.8p | £15.77 |
| 170p per litre | £34.35 | £68.70 | 17.2p | £17.17 |
| 173.97p per litre (average diesel price) | £35.15 | £70.30 | 17.6p | £17.58 |
Across that whole range the 200 mile leg only moves from £26.27 to £35.15, which is worth knowing before you drive out of your way to save two pence a litre. The last column is the number that changes minds about sharing a car: the same return trip split four ways lands near £15.77 a head.
If you do not know the distance
This is the honest limit of a distance-first tool, and the reason the RAC keeps its place in the comparison above. Calc Garden will not map a route for you, so if all you have is a start and an end postcode you need the mileage first. The RAC Route Planner will do it free, and so will any mapping app. Once you have the miles, read them off the table above or put them into the fuel cost calculator with your own mpg and pump price.
For a journey you make regularly it is worth writing the mileage down once. A commute, a weekly delivery round or a standing trip to see family has a distance that does not change, and after the first look-up the routing step is pure overhead. That is the case where typing the number straight in wins, and it is most of what people actually cost more than once.
When to pick each one
Reach for the RAC fuel cost calculator when the distance is the unknown. For a holiday drive, a one-off journey to somewhere new, or any trip where you want the miles, the driving time and the CO2 alongside the fuel cost, its routing is the reason to use it, and it is free. It is the better tool when the question is really "how far and how much" rather than just "how much".
Reach for the Calc Garden fuel cost calculator when the mileage is already in hand. It is the quicker, more transparent choice for a commute, a weekly round trip or a quoted distance, because you type the miles, mpg and price per litre, it opens with a worked example, updates the instant you change an input, shows the cost per mile and splits the total between passengers. If you also want to see what running a vehicle adds up to over a year, pair it with our electricity cost calculator for the rest of the household's running costs.
How to get an accurate fuel cost
Whichever tool you use, a few habits keep the result honest. Start with your real-world mpg, not the official combined figure, because everyday economy is usually 10 to 20 percent lower, and more on short urban runs. If your dashboard shows a long-term average, use that; otherwise take the official figure and knock off about 15 percent. The mpg input swings the total more than the pump price does, so a realistic figure matters most.
Use a current fuel price and remember to count both legs of a return trip, which is the most common way a quick estimate comes out half what it should be. A single calculator rarely tells the whole story, so pair the fuel cost with the tools around it. To check whether a price rise is really biting, the inflation calculator shows how costs change over time, and if you are budgeting toward a target, the savings goal calculator works out how fast you reach it. If you are weighing up other free calculators, the full guides index is a good next stop.