Estimate how far you can drive on a full tank of fuel
Knowing how far you can drive on a full tank is essential for planning journeys, budgeting fuel costs, and avoiding the stress of running out of fuel on an unfamiliar road. In the UK, where fuel is sold in litres but efficiency is measured in miles per gallon (imperial), calculating your actual range requires converting between two measurement systems. The average UK car has a fuel tank capacity between 40 and 60 litres, giving a typical range of 350 to 550 miles depending on the vehicle's fuel efficiency. However, most drivers rarely fill their tank completely to the brim, and a portion of the tank is considered reserve fuel -- the amount remaining when the fuel warning light illuminates. Understanding your usable range versus your reserve range helps you plan stops sensibly and avoid running dry. Fuel tank range is particularly useful when planning long motorway journeys, driving in rural areas where petrol stations are sparse, or comparing vehicles when purchasing a new car. A larger tank or more efficient engine translates directly into fewer fuel stops and greater convenience. This calculator takes your tank capacity, fuel efficiency in imperial MPG, and preferred reserve percentage to give you an accurate range estimate in both miles and kilometres.
To calculate your fuel tank range: 1. Enter your fuel tank capacity in litres. You can find this in your vehicle handbook, on the manufacturer's website, or by searching for your specific model online. Typical UK tank sizes: small cars 35-45 litres, medium cars 45-55 litres, large saloons and SUVs 55-75 litres, and some diesel 4x4s up to 80-100 litres. 2. Enter your fuel efficiency in miles per gallon (MPG). Use imperial MPG, which is the standard in the UK. You can find your real-world MPG from your trip computer, or use the official WLTP combined figure from the manufacturer (noting that real-world figures are typically 10-20% lower). Common real-world MPG: city cars 45-55, family hatchbacks 35-50, SUVs 25-40, performance cars 20-30. 3. Set the reserve percentage. This is the portion of the tank you want to keep as a safety buffer. The default 10% reflects the typical point at which the fuel warning light activates. You can increase this for extra peace of mind on long journeys or reduce it to zero to see the absolute maximum theoretical range. 4. Review the results. The range in miles shows how far you can drive on the usable fuel. The range in kilometres is provided for reference. The usable fuel and reserve volumes help you understand how much fuel you actually have to work with. The estimated cost of a full tank is calculated at 145 pence per litre, which is close to the UK national average for unleaded petrol. 5. For journey planning, compare your estimated range against the distance of your planned route. As a rule of thumb, plan to refuel when you have used about 75% of your tank to maintain a comfortable buffer.
The fuel tank range calculation uses UK imperial gallons (not US gallons): **Usable Fuel:** Usable fuel (litres) = tank capacity x (1 - reserve percentage / 100) For a 50-litre tank with 10% reserve: usable = 50 x 0.9 = 45 litres. **Converting Litres to Imperial Gallons:** Gallons = usable fuel / 4.546 One imperial gallon equals 4.546 litres. This is larger than a US gallon (3.785 litres), which is why UK MPG figures are higher than US MPG for the same vehicle. For our example: 45 / 4.546 = 9.90 imperial gallons. **Range in Miles:** Range (miles) = gallons x fuel efficiency (MPG) Simply multiply the available gallons by the miles per gallon. For 9.90 gallons at 40 MPG: 9.90 x 40 = 396 miles. **Range in Kilometres:** Range (km) = range (miles) x 1.60934 Converting to metric for reference: 396 x 1.60934 = 637 km. **Cost of Full Tank:** Cost = tank capacity (litres) x fuel price (pence per litre) / 100 At 145 pence per litre: 50 x 145 / 100 = GBP 72.50 for a full tank. **Practical Example:** A family hatchback with a 50-litre tank achieving 40 MPG in real-world driving, keeping 10% reserve: usable fuel = 45 litres = 9.90 imperial gallons, giving a range of approximately 396 miles or 637 km. At 145p per litre, a full tank costs GBP 72.50. This means each penny per litre increase in fuel price adds 50p to the cost of filling up, or roughly GBP 25 per year for a typical 10,000-mile annual mileage.