THE NUMORIX GUIDE
How to use the Running Pace Calculator
Last reviewed September 14, 2026
What this calculator does
In pace mode, the engine converts minutes and seconds to total seconds, divides by distance in kilometers, and formats the quotient as min/km.
Formula and method
In pace mode, the engine converts minutes and seconds to total seconds, divides by distance in kilometers, and formats the quotient as min/km. Speed is distance divided by total seconds times 3,600, and the same pace is extended over 5 km, 21.0975 km, and 42.195 km. Finish-time mode instead multiplies target distance by the entered seconds-per-kilometer pace.
Variables and inputs
Pace mode uses distance in km plus elapsed minutes and seconds. Finish-time mode uses target distance in km plus pace minutes and seconds per km. The engine displays pace as min/km, speed as km/h, and projected finishes as hours:minutes:seconds where needed.
Worked example
For 5 km in 25:00, total time is 1,500 seconds, so pace = 1,500 / 5 = 300 seconds/km = 5:00 min/km and speed = 5 / 1,500 x 3,600 = 12.0 km/h. Extending that pace gives 1:45:29 for a half marathon and 3:30:59 for a marathon after rounding seconds.
How to interpret the result
The output describes the average pace represented by the entered effort. The projected race times assume that pace remains unchanged over each standard distance; they are arithmetic projections, not predictions that account for fatigue, hills, weather, fueling, or race strategy.
Common mistakes to avoid
Enter distance in kilometers, not miles, unless you convert it first. Seconds are part of the elapsed time, so 25 minutes 30 seconds is 1,530 seconds rather than 25.30 minutes. In finish mode, keep pace seconds below 60; otherwise the valid-path check rejects the result.
Assumptions and limitations
The pace mode does not explicitly reject seconds of 60 or more, so malformed time input can produce a confusing formatted pace. The model assumes a constant pace and flat unit conversion; it does not model split variation, terrain, elevation, wind, temperature, training status, or the difference between a race effort and an easy run.