Calcpace is now a website

For four years, Calcpace was a piece of code. If you wanted to know what a 4:45/km pace turns into over a half marathon, you had to install a Ruby library and open a console — which rules out almost every runner alive.

That stops today. calcpace.app puts the same maths behind a form.

What you can do with it right now

• Work out pace, speed or finish time from any two of the three.
• Break a goal time into splits, so you know what each kilometre has to look like.
• Predict a race from a result you already have. Two formulas are offered, Riegel and Cameron, because they disagree — and where they disagree is useful information about how far you are extrapolating.
• Convert almost anything: kilometres and miles, metres, yards, feet, min/km and min/mi, km/h and mph, even knots. Metric or imperial, whichever you think in.

There is no account, no paywall and nothing to install. Open it on your phone at the start line if you want to.

Why the guides exist

Every calculator on the internet will hand you a number. Fewer will tell you where the number came from. Each tool here has a guide page next to it explaining the formula in plain language — including why Cameron tends to be more cautious than Riegel when you predict a marathon off a 5K, and what that should do to your expectations.

The calculations themselves are open source, and they always were. Now they have a front door.