Plain-English explanations
Fuel, EV and unit guides
29 original guides that explain the numbers behind the calculators. Each one starts with a direct answer, shows the formula, and tells you what it leaves out. No copied manufacturer copy and no invented live prices.
Start here
Foundation 01
Why UK and US MPG are different
The imperial and US gallons are not the same. Here is the exact conversion and why the same car can appear more efficient in Britain.
Read the guide →
Foundation 02
How trip fuel cost is calculated
The formulas behind the fuel cost calculator, including UK pence-per-litre pricing, US gallons and European litres per 100 km.
Read the guide →
Foundation 03
MPGe, mi/kWh and kWh/100 km explained
How EPA MPGe relates to real electric consumption, and how to compare it without confusing energy with liquid fuel.
Read the guide →
Fuel & units
MPG, L/100 km, km/L and the gallon traps that change the answer.
MPG to L/100 km: exact conversion
Convert MPG to L/100 km with the right constant for UK and US gallons, including worked examples and common mistakes.
Read the guide →
L/100 km to MPG: exact conversion
Turn litres per 100 kilometres into UK or US MPG with the exact formulas, examples and a simple way to remember the ratio.
Read the guide →
km/L to MPG: Japan, India and Korea
Understand kilometres per litre, convert it to MPG UK or US, and see why km/L is the inverse of L/100 km.
Read the guide →
US vs imperial gallon: MPG difference
The US and imperial gallons are different volumes. Learn the exact difference and how it changes MPG, fuel prices and cost comparisons.
Read the guide →
Fuel economy vs consumption
MPG and km/L measure distance per fuel. L/100 km measures fuel per distance. Here is why the distinction matters for comparisons and costs.
Read the guide →
Cost per mile formula: a plain-English guide
Calculate fuel cost per mile correctly for UK and US units, with examples and the mistake that makes estimates too low.
Read the guide →
Round-trip fuel cost formula
A simple method for round-trip fuel estimates, including detours, unit changes and the difference between one-way and return distance.
Read the guide →
Trip & budget
Turn distance, consumption and price into a practical fuel estimate.
How much fuel does 100 miles use? A simple guide
Work out fuel use and fuel cost for 100 miles in UK or US units, with example tables and the formula behind the answer.
Read the guide →
Fuel cost for 100 km: formula and examples
Calculate litres and fuel cost for 100 kilometres using L/100 km or km/L, with examples for Europe and Asia-Pacific markets.
Read the guide →
How to calculate commute fuel cost
A practical method for turning your daily commute into a fuel budget, including round trips, working weeks and real-world consumption.
Read the guide →
How to budget fuel for a road trip
Estimate road-trip fuel cost, add a sensible buffer and handle unit changes across countries without guessing.
Read the guide →
Track real fuel economy: tank-to-tank
Measure your car's real MPG or L/100 km using odometer readings and fill-ups, and avoid the common errors that distort the result.
Read the guide →
Driving
The habits and conditions that move real-world fuel use.
Does air conditioning use more fuel?
How car air conditioning affects fuel use, why speed changes the answer, and when open windows are the better choice.
Read the guide →
Do roof boxes and roof racks increase fuel use?
Why roof accessories add drag, how speed makes the effect worse, and how to measure the real cost on your own car.
Read the guide →
Tyre pressure and fuel economy
How under-inflated tyres affect rolling resistance, how to check pressure correctly, and why over-inflating is not a free fix.
Read the guide →
Does idling waste fuel?
Why idling is inefficient, when switching off makes sense, and how idling affects a simple fuel-cost estimate.
Read the guide →
What is the most fuel-efficient speed?
Why there is no universal magic speed, how aerodynamic drag changes the picture, and how to find an efficient pace for your car.
Read the guide →
Towing and fuel economy
Understand how trailers affect fuel use, why drag matters, and how to budget for a towing trip with a realistic MPG.
Read the guide →
City vs highway MPG explained
Compare city and highway fuel use for petrol cars, hybrids and EVs, and choose the right figure for your route.
Read the guide →
EV & charging
kWh, charging losses, range and running-cost comparisons.
kWh/100 km explained: the EV version of L/100 km
Learn what kWh/100 km means, how to turn it into cost per 100 km, and how it differs from mi/kWh and battery-side efficiency.
Read the guide →
mi/kWh vs km/kWh: EV efficiency units made simple
Convert miles per kWh to kilometres per kWh and kWh/100 km, and understand which direction means better efficiency.
Read the guide →
EV charging losses explained
Why the electricity you pay for is not all stored in the battery, the charging-loss formula, and how to avoid double counting.
Read the guide →
Home vs public EV charging cost
Compare home and public charging on all-in cost per kWh, including session fees, charging losses and convenience.
Read the guide →
EV vs petrol break-even: how to calculate it
Estimate the annual running-cost saving from an EV and the years needed to recover a purchase-price difference.
Read the guide →
Why EV range drops in cold weather
How cabin heating and battery temperature affect EV range, and how to build a realistic winter estimate.
Read the guide →
Hybrid vs petrol running cost
Compare hybrid and petrol fuel costs using the same annual distance, realistic MPG and your own fuel price.
Read the guide →
Page last reviewed: . Formulas are covered by automated tests. Prices are inputs, not live data.