About Bike Speed Calculator
A small, free set of cycling calculators built on published models — speed and pace, gearing, power, triathlon splits and indoor riding — each one showing its working.
Why this site exists
I kept meeting the same three questions on rides and in training logs: what average does that work out to, what speed does this gear give me, and what does that wattage actually buy? The answers online were usually a bare number with no formula, no defaults and no way to check it. This site is my attempt at the opposite — every calculator prints its method, names its constants and shows a worked example you can verify with a pencil.
Start with the bike speed calculator for everyday ride maths, the gear speed calculator for drivetrain questions, and the methodology page if you want the models themselves.
How the tools are built
Each tool starts from a published source: the power calculator implements the peer-reviewed power-balance model of Martin and co-authors; the gear calculator follows the standard gain-ratio conventions documented in Sheldon Brown’s gear pages; the erg converter applies the erg maker’s published cubic unchanged. I compute a set of reference cases by hand first, then pin them in automated tests, so a change that breaks the arithmetic cannot ship quietly.
A note on AI
Honestly: I use AI tools to help draft and code this site. Nothing an AI produces goes live unchecked — every formula is traced to its published source, every worked example is computed by hand, and the test suite re-verifies the numbers before each release. Where a number on this site is wrong, that is my error, and the report an error page is the fastest way to get it fixed.
Who runs it
Bike Speed Calculator is built and maintained by Ian Welkins, working from Houston, Texas. Questions, corrections and requests are welcome through the contact page.