About
Last updated: 23 October 2026
RoadNumbers is a small, independent site with calculators for everyday car questions: will these tires fit, how wrong is my speedometer now, what will this trip cost in fuel?
RoadNumbers is owned and operated by LIV Technologies Limited, a company registered in Gibraltar with company number 126033, whose registered office is at Suites 1 & 2, Newton House, 5 Kings Yard Lane, P.O. Box 140, Gibraltar. Email: [email protected].
How we build the calculators
- Exact formulas. Every page explains the formula it uses and shows a worked example you can check by hand.
- Tested. Each formula is covered by automated tests against reference values before the site is published.
- Fast and private. Calculations run in your browser. There are no accounts and no forms.
- US, UK and metric. Inches and millimetres, miles and kilometres, US and imperial gallons.
Where the data comes from
- Tire and wheel sizes by vehicle: Swiss Federal Roads Office (FEDRO/ASTRA), open government data — the official type-approval records for cars sold in Switzerland.
- US fuel economy: U.S. EPA and U.S. DOE (fueleconomy.gov), official data download.
- UK fuel economy: Vehicle Certification Agency (VCA), Car Fuel Data, official data download (© Crown copyright, CC BY as listed on data.gov.uk).
We only use official open-data downloads, never data copied from other websites, and we name the source on every page that uses it.
Corrections
Found a mistake? Email [email protected] with the page address and we will check it.