Pace Converter

Features

• Pace per km, per mile and per 100 m (swimming), written the way a stopwatch shows it: `m:ss`
• Speed in km/h, mph and m/s
• ⚠️ The result states that pace and speed are reciprocal, and advises converting both to km/h before averaging
• Finish times for the standard distances: 1 km, 5 km, 10 km, half marathon 21.0975 km, marathon 42.195 km
• Add your own distance in kilometres and it is computed too
• Accepts `5:30` (stopwatch form) and `5.5` (5.5 minutes)
• Miles use the exact 1609.344 m, not a rounded 1.609
• ⚠️ Very slow speeds are never shown as 0 (significant digits, not a fixed number of decimals)
• Runs entirely in your browser

How to use

1. Pick what your number is under “what the input is”
2. Enter the pace or the speed
3. The result gives all six units plus finish times for the standard distances

FAQ

Why is pace not in the unit converter?

Because it relates to speed reciprocally: `km/h = 3.6 ÷ seconds per km`. Proportional conversions satisfy “0 maps to 0”, but a pace of zero is infinite speed. The practical problem is midpoints: between `5:00/km` and `10:00/km`, averaging the paces gives `7:30/km` while averaging the speeds gives `6:40/km` — 50 seconds apart, and the second is correct. Offer it as a proportional conversion and everyone doing mental arithmetic gets it wrong, so it needs its own page.

Is `5.5` five minutes thirty or five minutes five?

Five minutes thirty — 5.5 minutes. Both readings look plausible and differ by 25 seconds, so this is defined as minutes. Safer still is `5:30`, the stopwatch form, which cannot be misread.

Why is a half marathon 21.0975 km rather than 21 km?

Because it is half of the marathon, and the marathon is 42.195 km, the IAAF race distance. Those 97.5 metres are 29 seconds on a 3:30 finish — enough to decide whether a qualifying time is met. Estimating with 21 km runs consistently fast.

Why per 100 m for swimming?

Because that is the convention: pools are 25 or 50 m and results are printed per 100 m. The conversion is easy — seconds per 100 m times ten gives seconds per km — but both are listed here so you do not have to do it.

Why not show a very slow speed as 0?

Because that tells the reader they are not moving. Below 1 the tool uses significant digits rather than a fixed number of decimals — a 30-minute-per-100 m swim pace is about 0.056 m/s and still displays, but anything slower would collapse to `0.000`. Showing a non-zero value as zero is the kind of error that makes people think the tool is broken.