25 definitions covering fuel economy, UK fuel prices, MPG testing, and the data behind WorthThePump — explained clearly for UK drivers.
Start with the basics: MPG, Real-World MPG, and Break-Even Distance. For how prices work: Fuel Duty and the CMA Transparency Mandate.
25
Terms
6
Categories
37k+
Stations
UK
Focused
A–Z Index
How fuel efficiency is measured, tested, and why the number on the brochure rarely matches the real world.
MPG (Miles Per Gallon)
A measure of fuel efficiency expressing how many miles a vehicle travels on one gallon of fuel. The higher the MPG, the more economical the car — and the less each mile costs you.
Real-World MPG vs Official MPG
Real-world MPG is the fuel economy a driver actually achieves on public roads — typically 12–25% lower than the official figure measured in a lab. The gap exists because test cycles can't fully replicate traffic, weather, air conditioning, and driving style.
WLTP Test Cycle
The Worldwide Harmonised Light Vehicle Test Procedure (WLTP) is the official EU and UK fuel economy test that replaced NEDC in 2017–2019. It uses more realistic speeds, durations, and equipment options to produce fuel consumption figures closer to real-world driving.
NEDC Test Cycle
The New European Drive Cycle (NEDC) was the EU's official fuel economy test from 1997 until 2019. It was replaced by WLTP because its unrealistically smooth speeds and minimal air-con use produced figures up to 40% higher than real-world results.
Hypermiling
A driving technique that maximises fuel efficiency by minimising unnecessary acceleration, braking, and idling. Skilled hypermilers routinely achieve 20–40% better fuel economy than the same car under normal driving — sometimes exceeding official MPG figures.
Tankful (Full Tank)
The amount of fuel needed to fill a vehicle's tank from its current level to maximum capacity. The fill amount is a critical input in the detour calculation — the more you fill, the bigger the gross saving from a cheaper price per litre, and the further it's worth driving.
The different grades of petrol and diesel sold at UK forecourts — what's in them and whether it matters.
E10 Petrol
E10 is the standard grade of unleaded petrol sold across the UK since September 2021. It contains up to 10% bioethanol blended with 90% conventional petrol, reducing carbon emissions. Most petrol cars made after 2011 are compatible.
B7 Diesel
B7 is the standard diesel grade sold at UK forecourts. It contains up to 7% biodiesel (FAME — fatty acid methyl esters) blended with conventional diesel. The 'B7' designation indicates the maximum biodiesel content is 7% by volume.
Research Octane Number (RON)
RON measures the knock resistance of a petrol fuel — how much it can be compressed before igniting spontaneously. Standard UK unleaded is RON 95 (E10). Premium unleaded is RON 97–99. Higher RON fuels can improve efficiency in some engines.
Branded vs Unbranded Fuel
Branded fuel (Shell, BP, Esso, Texaco) includes proprietary additive packages claimed to clean injectors and improve efficiency. Unbranded fuel (supermarkets, independents) meets the legal minimum standard (BS EN 228 for petrol, BS EN 590 for diesel) without the premium additives.
Supermarket Petrol
Petrol and diesel sold by UK supermarket chains (Tesco, Asda, Morrisons, Sainsbury's). Supermarket fuel is consistently the cheapest on the UK market — typically 3–8p per litre less than branded forecourts — due to high volume, thin margins, and loss-leader pricing.
The core concepts behind working out whether a cheaper station is genuinely cheaper once you factor in the drive.
Break-Even Distance
The maximum distance you can travel to a cheaper fuel station before the fuel cost of the detour wipes out the price saving entirely. If the station is closer than the break-even distance, you save money; if it's farther, you don't.
Net Saving vs Gross Saving
Gross saving is the raw price difference multiplied by your fill volume. Net saving subtracts the fuel cost of driving to the cheaper station. Only the net saving is money you actually keep.
Detour Cost
The fuel cost of driving to and from a cheaper petrol station. Detour cost is subtracted from the gross saving to calculate the true net saving. It depends on your car's MPG, the current fuel price, and the distance to the station.
Dead Mileage
Miles driven that don't contribute to a productive purpose — such as driving to a petrol station that's out of your way. Dead mileage burns fuel and costs money without advancing your journey.
Haversine Distance Formula
A formula that calculates the great-circle distance between two points on Earth's surface using their latitude and longitude coordinates. WorthThePump uses the Haversine formula to measure how far each petrol station is from your current location.
How pump prices are made up, what goes to the government, and how UK fuel is priced and regulated.
Pence Per Litre (PPL)
The standard unit for expressing UK fuel prices. All petrol and diesel prices are shown as pence per litre (p/L or PPL) on forecourt signs, price-comparison apps, and the UK Government's Fuel Finder API.
Fuel Duty (UK)
A UK government excise tax levied on every litre of petrol or diesel sold. As of 2025, fuel duty is 52.95p per litre — the single largest component of the price you see on the forecourt.
VAT on Fuel
Value Added Tax (VAT) at 20% applies to the entire pump price, including fuel duty. VAT is the second-largest tax component in the price of a litre of petrol or diesel.
CMA Fuel Price Transparency Mandate
A regulatory requirement introduced by the UK Competition and Markets Authority (CMA) in 2023 requiring petrol retailers to report near-real-time fuel prices to a government-run database, powering free public price comparison tools including the UK Fuel Finder API.
Fuel Card
A payment card used by businesses and fleet drivers to purchase fuel, with centralised billing, mileage tracking, and often negotiated discounts at participating stations. Examples include the BP Plus card, Shell Fleet Card, and AllStar Business Solutions.
The government and DVLA data sources that power WorthThePump's live prices and vehicle lookups.
UK Government Fuel Finder API
A free government-mandated API that provides near-real-time petrol and diesel prices from over 37,000 UK fuel stations. It was launched in November 2023 as part of the CMA's fuel price transparency initiative.
DVLA VES API
The Driver and Vehicle Licensing Agency's Vehicle Enquiry Service (VES) API allows applications to look up UK-registered vehicle details — including make, model, fuel type, engine size, and CO2 emissions — using a number plate (VRN).
Vehicle Registration Number (VRN / Number Plate)
The unique alphanumeric identifier assigned to every UK vehicle by the DVLA. In the current format (e.g., AB23 CDE), the letters encode the registration office, year, and a unique suffix. WorthThePump uses your VRN to look up your car's fuel type and MPG automatically.
The environmental impact of petrol and diesel — CO2 per litre, lifecycle emissions, and what helps.
What is MPG and how does it affect fuel saving calculations?
MPG (Miles Per Gallon) measures how far your car travels on one gallon of fuel. Higher MPG means a cheaper cost-per-mile — and a lower fuel cost when driving to a cheaper station. WorthThePump derives your MPG from your number plate via the DVLA VES API. Read the full MPG definition →
Why is real-world MPG lower than the official figure?
Official figures come from lab test cycles (WLTP or NEDC). Real driving — traffic, motorway speeds, air conditioning, cold starts — is harder on consumption. Real-world MPG is typically 12–25% lower. See Real-World MPG →
How does the UK Government Fuel Finder API work?
Under the CMA transparency mandate, all UK retailers must report prices within 30 minutes of any change. The government aggregates this into a free API covering 37,000+ stations. See Fuel Finder API →
What is the break-even distance for a cheaper fuel station?
The break-even distance is how far you can travel to a cheaper station before the fuel cost wipes out your saving. It depends on your MPG, the price difference, and your fill volume. See Break-Even Distance →