Common race distances
Enter any two of the three values — distance, time, and pace — and the calculator works out the third for you automatically. Pace is shown as minutes and seconds per kilometre or mile, the standard way runners measure how fast they're going.
Pace, time, and distance are three ways of describing the same run — knowing any two always tells you the third: pace = time ÷ distance, distance = time ÷ pace, and time = distance × pace. Whichever field you last typed into stays editable; the calculator picks one of the other two fields to compute automatically (shown highlighted and read-only), preferring pace as the default calculated value when more than one field could be filled in.
The 5K, 10K, half marathon, and marathon buttons drop the standard distance for that race straight into the distance field, so you only need to enter a time (or a target pace) to see what finish time or pace you'd need.
The unit toggle converts whatever distance and pace values are already entered, rather than clearing them, so you can compare the same run in either unit. The result summary always shows the equivalent pace in the other unit as well.
This is a straightforward pace/time/distance conversion — it doesn't account for elevation, terrain, weather, or how pace typically varies over the course of a run. Use it for planning and comparison, not as a guarantee of race-day performance.