How pace, time, and distance relate
Three variables define every run: distance, total time, and pace (time per unit of distance). Knowing any two tells you the third:
Where pace is in seconds per km (or per mile), total time in seconds, and distance in km (or miles). The calculator handles the unit conversion between km and miles internally.
Common race distances
| Race | Distance |
|---|---|
| 5K | 5.000 km |
| 10K | 10.000 km |
| Half marathon | 21.097 km |
| Marathon | 42.195 km |
Click any race preset button in the calculator to fill in the distance automatically. Your current time and pace values stay in place, so the result updates immediately.
Example: planning a marathon at 5:30 per km
A 5:30 per km pace over 42.195 km gives:
Select “Find time”, click the Marathon preset, enter 5:30 as pace, and the calculator shows 3:52:04.
To work backwards — say you want to finish in exactly 3:45:00 — select “Find pace”, click Marathon, enter 3:45:00 as total time. The result is approximately 5:20 per km (the target pace you need to hold).
Training pace vs race pace
The calculator tells you the math. It does not tell you whether you can run that fast. Recreational runners often underestimate how much slower their easy training runs should be relative to race effort.
Most distance coaches use the 80/20 principle: about 80% of weekly running volume at conversational easy pace (typically 60–90 sec per km slower than 5K race pace), and 20% at harder efforts. Running exclusively at race pace or near it accumulates fatigue faster than the body can absorb and adapt.
Use the calculator to set realistic race targets based on recent time trials or race results, then build your training paces around those anchor points. For converting distances between km and miles before entering them, the length converter is the direct route; for converting an average speed (km/h or mph) to pace, the speed converter handles the unit shift.