Motoring units, formulas and reference values
A compact reference for the relationships used across MotoringCalcs. Exact conversions are separated from vehicle-specific assumptions.
Reviewed 6 September 2026UK units unless statedCalculations and assumptions shown
Fuel & distance
| Relationship | Value / formula | Use |
|---|---|---|
| Imperial gallon | 4.54609 litres | UK MPG calculations |
| Mile | 1.609344 km | Distance conversion |
| UK MPG ↔ L/100km | L/100km = 282.481 ÷ MPG | Fuel-economy comparison |
| Journey litres | miles ÷ MPG × 4.54609 | Fuel budgeting |
| Fuel cost | litres × £/litre | Journey / annual fuel cost |
EV charging & energy
| Relationship | Formula | Important assumption |
|---|---|---|
| Battery energy added | battery kWh × percentage points added ÷ 100 | Battery percentage is an estimate |
| Wall energy | battery energy ÷ charging efficiency | Efficiency varies by equipment and conditions |
| Charging cost | wall kWh × p/kWh ÷ 100 | Use the rate that actually applies |
| EV energy per mile | 1 ÷ miles/kWh | Use real-world efficiency where possible |
Power & torque
| Conversion | Reference relationship |
|---|---|
| Mechanical hp to kW | hp × 0.745699872 |
| PS to kW | PS × 0.73549875 |
| kW to mechanical hp | kW × 1.34102209 |
| Nm to lb-ft | Nm × 0.737562149 |
| lb-ft to Nm | lb-ft × 1.35581795 |
| HP from torque and RPM | lb-ft × RPM ÷ 5252 (approx. constant) |
Tyre geometry
Sidewall mm = width × profile ÷ 100
Wheel mm = wheel inches × 25.4
Diameter = wheel mm + 2 × sidewall
Circumference = π × diameter
These are nominal geometric relationships. Actual tyre dimensions and approved fitment should be checked against tyre and vehicle-manufacturer information.