Gallons per 100 miles (UK) to Gallons per 100 miles (US)
gal/100mi (UK)
gal/100mi (US)
Conversion History
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Quick Reference Table (Gallons per 100 miles (UK) to Gallons per 100 miles (US))
| Gallons per 100 miles (UK) (gal/100mi (UK)) | Gallons per 100 miles (US) (gal/100mi (US)) |
|---|---|
| 1.4 | 1.681329895873228983283499318418 |
| 1.7 | 2.041614873560349479731759437186 |
| 2 | 2.401899851247469976180019555954 |
| 2.5 | 3.002374814059337470543882225566 |
| 3 | 3.60284977687120496448260118768 |
| 3.5 | 4.203324739683072458421320149794 |
| 5 | 6.004749628118674940662620743634 |
About Gallons per 100 miles (UK) (gal/100mi (UK))
Gallons per 100 miles (imperial) is the British consumption-oriented counterpart to the metric L/100km standard, expressing how many imperial gallons a vehicle burns over 100 miles. It is numerically distinct from its US equivalent because the imperial gallon (4.546 L) is larger than the US gallon (3.785 L), so UK gal/100mi values are roughly 20% lower than US gal/100mi for identical fuel consumption. The unit is used in UK engineering and fleet management contexts where consumption rather than efficiency framing is preferred, and in academic analysis of British vehicle fuel-use data.
A 50 UK mpg car consumes 2 gal/100mi (imperial). A typical British family SUV at 35 UK mpg uses about 2.86 gal/100mi (imperial).
About Gallons per 100 miles (US) (gal/100mi (US))
Gallons per 100 miles (US) — abbreviated gal/100mi — is a consumption metric, the American analogue to the European L/100km standard. Lower is better. It is the mathematical inverse of US mpg multiplied by 100. The US EPA introduced the GPM metric alongside mpg to help consumers make better fuel economy comparisons: because mpg is non-linear, the true fuel saving from improving a 15 mpg truck to 20 mpg (1.67 gal/100mi saved) is far larger than improving a 40 mpg car to 50 mpg (0.5 gal/100mi saved). GPM makes this intuitively clear by expressing absolute consumption rather than efficiency.
A 25 mpg family sedan consumes 4 gal/100mi. A 50 mpg hybrid uses only 2 gal/100mi — saving as much fuel per mile as the difference from 10 to 50 mpg on a low-efficiency vehicle.
Gallons per 100 miles (UK) – Frequently Asked Questions
Why would anyone use imperial gallons per 100 miles?
Fleet managers and logistics companies in the UK sometimes prefer this consumption-based metric because it scales linearly with cost. If fuel costs £5.50 per imperial gallon, a vehicle using 3 gal/100mi costs exactly £16.50 per 100 miles — much easier to budget than working backwards from mpg.
How does UK gal/100mi compare to US gal/100mi for the same car?
UK gal/100mi values are about 17% lower than US gal/100mi because the imperial gallon is larger. A car consuming 4 US gal/100mi uses only about 3.33 UK gal/100mi. Same fuel burned, but fewer of the bigger gallons needed to measure it.
How do UK fleet operators use gal/100mi to set carbon budgets per vehicle?
Burning one imperial gallon of diesel produces about 10.2 kg of CO₂. Multiplying gal/100mi by that emission factor gives a direct kg-CO₂-per-100-miles figure for each vehicle. Fleet managers set thresholds — say 25 kg CO₂/100mi — and flag any vehicle exceeding it for maintenance or driver retraining. The linear relationship makes gal/100mi far better than mpg for carbon accounting, where small absolute savings matter.
What is a good UK gal/100mi for a family car?
A modern family hatchback should achieve around 1.8–2.3 UK gal/100mi (43–56 UK mpg). Anything under 2 gal/100mi is considered very efficient. SUVs typically sit at 2.5–3.5 gal/100mi, and performance cars can exceed 4 gal/100mi.
Is this unit used on any official UK documentation?
Not on consumer-facing documents. UK vehicle registration (V5C) and type-approval certificates show L/100km and CO₂ g/km. Gal/100mi (imperial) lives mainly in fleet management software, academic transport research, and engineering reports where linear consumption comparisons matter more than the traditional mpg framing.
Gallons per 100 miles (US) – Frequently Asked Questions
Why did the EPA start showing gallons per 100 miles on window stickers?
Research by Duke University professors showed that mpg systematically misleads consumers about fuel savings. The EPA added gal/100mi to Monroney stickers starting in 2013 to give buyers a linear, comparable number. A 1 gal/100mi difference always represents the same fuel saving regardless of starting point.
How does gal/100mi help compare plug-in hybrids that switch between fuel and electricity?
Plug-in hybrids complicate mpg because they drive some miles on electricity and some on petrol. Gal/100mi lets you weight the two modes transparently: if a PHEV uses 0 gallons for its first 40 electric miles and 2.5 gal/100mi after that, fleet managers can model exact fuel costs for any commute length. The EPA's MPGe tries to do something similar for consumers, but gal/100mi is more intuitive for mixed-mode budgeting.
What gal/100mi does the average American car use?
The average new car in the US uses about 3–4 gal/100mi (25–33 mpg). Full-size trucks sit around 5–7 gal/100mi, while hybrids achieve 1.5–2.5 gal/100mi. Electric vehicles show 0 gal/100mi but have a separate kWh/100mi rating.
Why do long-haul trucking companies obsess over fractions of a gal/100mi?
A Class 8 semi averages about 6.5 gal/100mi and covers 100,000+ miles per year — roughly 6,500 gallons annually. Shaving just 0.3 gal/100mi through aerodynamic fairings, low-rolling-resistance tires, or driver coaching saves ~300 gallons per truck per year. Across a 5,000-truck fleet, that is 1.5 million gallons saved — worth over $5 million at US diesel prices. At that scale, every tenth of a gal/100mi is a budget line item.
Why do Europeans never use gal/100mi even though they use L/100km?
Europeans adopted L/100km as their native metric from the start, so there was never a need for an alternative. Gal/100mi was invented specifically to fix the mpg illusion problem in the US. Europeans already had the "right" unit — they just used metric volumes and distances.