A typical UK car now costs about £64.64 to £96.96 to fill with petrol, depending on whether its tank holds 40 or 60 litres. A diesel car with the same tank sizes costs about £73.00 to £109.50. These figures use PetrolPal's live national averages of 161.6p for petrol and 182.5p for diesel on 12 August 2026 (PetrolPal, 2026).
Most drivers don't arrive with a completely empty tank. Filling a 55-litre tank from 10% remaining needs 49.5 litres. At current averages, that costs about £79.99 for petrol or £90.34 for diesel. Your final bill depends on tank capacity, fuel remaining, fuel grade, and the station you choose.
How Much Does It Cost to Fill Different Car Tank Sizes?
At 161.6p per litre, every ten litres of petrol costs £16.16. At 182.5p, ten litres of diesel costs £18.25 (PetrolPal, 2026). Multiply your tank capacity by the price per litre, then adjust for the fuel already present.
| Tank size | Petrol, full tank | Diesel, full tank | Petrol, from 10% | Diesel, from 10% |
|---|---|---|---|---|
| 40 litres | £64.64 | £73.00 | £58.18 | £65.70 |
| 45 litres | £72.72 | £82.13 | £65.45 | £73.91 |
| 50 litres | £80.80 | £91.25 | £72.72 | £82.13 |
| 55 litres | £88.88 | £100.38 | £79.99 | £90.34 |
| 60 litres | £96.96 | £109.50 | £87.26 | £98.55 |
| 70 litres | £113.12 | £127.75 | £101.81 | £114.98 |
The table uses simple multiplication, not a forecast. Pump prices can change between checking and arriving. The live PetrolPal data covered 8,045 stations, with 7,819 unleaded prices and 7,905 diesel prices in the detailed dataset (PetrolPal, 2026).
Don't know your tank size? Check the vehicle handbook or manufacturer specification. A dashboard range estimate doesn't reveal capacity reliably. It changes with driving style, weather, traffic, and recent fuel economy.
A useful budget figure is the cost of 90% of capacity, not the full published tank size. Drivers commonly fill before the warning reaches zero. This method turns a 55-litre petrol tank from an £88.88 theoretical maximum into a more realistic £79.99 transaction.
A 55-litre tank filled from 10% remaining needs 49.5 litres. PetrolPal's 12 August averages put that purchase at £79.99 for petrol and £90.34 for diesel (PetrolPal, 2026). That calculation gives households a better cash-flow estimate than assuming every visit starts empty.
Use PetrolPal's live fuel map to replace the national average with a reachable local price.
Why Does the Same Tank Cost More at Some Stations?
PetrolPal found average unleaded at 159.2p at supermarkets and 162.6p at branded forecourts, a 3.5p gap (PetrolPal, 2026). On 55 litres, that category-level difference is about £1.90. Diesel showed a wider 4.7p gap, worth about £2.59.
Station type isn't a guarantee. A nearby branded site can beat a supermarket, while a poorly placed detour can consume any saving. Compare actual stations close to your route. National category averages describe the market, but they don't select the best stop for one journey.
PetrolPal's detailed averages placed unleaded at 159.17p for supermarkets, 161.03p for independents, and 162.63p for branded sites. Diesel averaged 178.78p, 181.12p, and 183.49p across those same groups (PetrolPal, 2026).
Why chase a station ten miles away to save £2? A separate trip adds fuel, time, and wear. A lower price becomes useful when the station sits near home, work, or an existing route. PetrolPal's route planner helps compare stops without inventing a costly detour.
The live data shows a practical difference between petrol and diesel shopping. The average 55-litre supermarket saving was £1.90 for petrol, but £2.59 for diesel. Diesel drivers therefore had 36% more category-level value available from station choice during this snapshot.
A 3.5p petrol gap and 4.7p diesel gap look small on a roadside sign. They become £1.90 and £2.59 across 55 litres (PetrolPal, 2026). Compare the total fill cost, not only the last digit shown per litre.
What Makes Up the UK Pump Price?
Fuel duty on standard petrol and road diesel is 52.95p per litre through 31 December 2026 (HMRC, 2026). VAT uses the standard 20% rate (GOV.UK, 2026). The remaining price covers the fuel, distribution, biofuel obligations, and retailer margin.
VAT applies to the final pre-VAT price, including fuel duty. At a 161.6p petrol price, the VAT portion is about 26.9p. Add 52.95p duty, and those two taxes total about 79.9p per litre. That is roughly 49% of the displayed petrol price.
For diesel at 182.5p, VAT contributes about 30.4p per litre. Combined with 52.95p duty, the tax amount is about 83.4p. The tax share is lower as a percentage, near 46%, because the total diesel price is higher.
These are calculated tax components, not claims about retailer profit. Wholesale prices and margins move. The government publishes a weekly road-fuel series for national tracking (DESNZ, 2026). RAC Fuel Watch also follows pump and wholesale movements (RAC, 2026).
Does a 1p wholesale move always reach the pump immediately? No. Retailers buy at different times, carry stock, face different delivery costs, and set prices for local competition. That lag helps explain why forecourts on the same road can move on different days.
At 161.6p per litre, petrol includes about 26.9p VAT and 52.95p fuel duty, totalling about 79.9p in calculated tax (HMRC; GOV.UK). Station comparison still matters because the non-tax part varies across suppliers and locations.
Does Petrol or Diesel Cost More to Fill?
Diesel averaged 182.5p per litre, 20.9p above petrol's 161.6p, on 12 August 2026 (PetrolPal, 2026). That difference adds £11.50 to a full 55-litre tank. It adds about £10.35 when filling from 10% remaining.
| Purchase | Petrol | Diesel | Diesel premium |
|---|---|---|---|
| 40-litre full tank | £64.64 | £73.00 | £8.36 |
| 55-litre full tank | £88.88 | £100.38 | £11.50 |
| 60-litre full tank | £96.96 | £109.50 | £12.54 |
| 55-litre tank from 10% | £79.99 | £90.34 | £10.35 |
A higher fill price doesn't prove that diesel costs more per mile. Diesel engines often use fewer litres over the same distance. The correct comparison uses each vehicle's real miles per gallon, annual mileage, insurance, servicing, tax, and purchase price.
For a simple fuel-only comparison, divide miles travelled by miles per gallon. Convert gallons to litres, then multiply by the local price. Use your recorded consumption rather than a brochure figure. Short urban trips can produce very different results from long motorway runs.
The current diesel premium is large enough to change cash flow before it changes lifetime economics. A driver might spend £10.35 more during one 90% fill, even if stronger diesel economy later recovers part of that amount. Monthly budgets and ownership decisions therefore need separate calculations.
PetrolPal's snapshot puts the diesel premium at 20.9p per litre across 8,045 stations (PetrolPal, 2026). On 49.5 litres, that creates a £10.35 checkout difference before mileage and efficiency enter the calculation.
How Can You Calculate Your Exact Fill-Up Cost?
The exact formula is litres bought multiplied by price in pounds per litre. A 49.5-litre purchase at 159.9p costs £79.15. Convert pence to pounds by dividing by 100, then multiply. PetrolPal's map provides the station price needed for this calculation (PetrolPal, 2026).
Follow these steps:
- Find your vehicle's tank capacity in litres.
- Estimate the fuel remaining as a percentage.
- Multiply capacity by the empty percentage.
- Divide the pump price in pence by 100.
- Multiply litres needed by the price in pounds.
For example, a 55-litre tank at one-quarter full needs about 41.25 litres. At 161.6p, petrol costs £66.66. At 182.5p, diesel costs £75.28. The gauge is not a precision instrument, so treat the answer as a budget estimate.
Can the pump take more than the handbook capacity suggests? The filler neck and measurement tolerances can affect the displayed volume. Never force extra fuel after the nozzle clicks. The first automatic stop is the safe point for normal filling.
A 55-litre tank at 25% remaining needs an estimated 41.25 litres. Using current national averages, that is £66.66 for petrol or £75.28 for diesel (PetrolPal, 2026). Local station prices can move both results by several pounds.
Save your regular tank size in a note. Then each price check needs one multiplication, not a fresh vehicle search. PetrolPal's fuel price pages provide current national context before you compare nearby sites.
How Can You Spend Less on Each Fill?
The strongest immediate saving is station choice. PetrolPal's current supermarket-to-branded gap saves about £1.90 on 55 litres of petrol and £2.59 on diesel (PetrolPal, 2026). Larger local gaps can save more, but only when the cheaper stop fits your route.
Check prices before the warning light forces an urgent stop. Urgency removes choice. Keeping enough fuel for normal journeys lets you select a better station near an existing destination.
Avoid judging value from price alone. Multiply the per-litre gap by the litres you expect to buy. A 2p saving on 40 litres is only 80p. A long detour rarely makes sense for that amount.
Use these practical rules:
- Compare reachable stations, not the cheapest national listing.
- Fill near an existing journey and avoid a special trip.
- Calculate the full saving before choosing a detour.
- Keep tyres at the vehicle maker's recommended pressure.
- Remove unnecessary roof boxes when they aren't in use.
- Record real fuel economy to spot a sudden change.
Would filling only halfway reduce fuel use enough to matter? A lighter car can use slightly less fuel, but repeated station visits add inconvenience and possible detours. For most drivers, buying at a well-priced station matters more than carrying a few fewer litres.
A 4.7p diesel category gap saves £2.59 across 55 litres, while a 3.5p petrol gap saves £1.90 (PetrolPal, 2026). Plan around actual journey routes, because the cheapest listed price isn't a saving if reaching it costs more.
What Is the Current Bottom Line?
A 55-litre fill costs about £88.88 for petrol or £100.38 for diesel at current national averages (PetrolPal, 2026). Filling from 10% remaining lowers those estimated payments to £79.99 and £90.34. The biggest variables are tank size, fuel left, grade, and station.
For the best local estimate, find your tank size and check the actual station price. Multiply the litres needed by the price per litre. Then compare only stops that fit an existing journey.
PetrolPal tracks thousands of UK forecourts through its live map, fuel price pages, and route planner. A national average answers the budget question. A local comparison decides what you pay today.