Pace Calculator
Calculate your running pace, finish time, or distance covered. Includes projected race times for 5K, 10K, half marathon, and marathon.
How to Use the Pace Calculator
Choose a tab based on what you want to calculate. "Find Pace" tells you your min/km pace from a known distance and time. "Find Time" projects how long a given distance will take at your target pace. "Find Distance" shows how far you can run in a set time at a given pace.
The Extended Calculator below adds a negative split planner and uses the Riegel formula to predict race times from a known result. The Professional Calculator adds altitude and heat adjustment, a race strategy planner, and the Comrades Marathon checkpoint guide.
Race Time Predictor (Riegel Formula)
| Distance | Predicted Time | Pace |
|---|---|---|
| 5K | 23:59 | 4:48/km |
| 10K | 50:00 | 5:00/km |
| 21.1K (Half) | 1:50:19 | 5:14/km |
| 42.2K (Full) | 3:50:01 | 5:27/km |
| 56K (Comrades approx) | 5:10:29 | 5:33/km |
| 89K (Comrades approx) | 8:27:22 | 5:42/km |
Formulas
Pace (min/km): Total Time (seconds) ÷ Distance (km) → convert to mm:ss
Finish Time: Pace (seconds/km) × Distance (km)
Distance: Total Time (seconds) ÷ Pace (seconds/km)
Riegel Race Predictor: T2 = T1 × (D2 ÷ D1)^1.06
Common Race Distances
| Race | Distance | SA Event |
|---|---|---|
| 5K | 5.000 km | Parkrun, entry-level road races |
| 10K | 10.000 km | Popular road race |
| Half Marathon | 21.0975 km | Two Oceans Short, Sanlam Cape Town Half |
| Marathon | 42.195 km | Cape Town Marathon, Comrades qualifier |
| Comrades | ~89 km | World's greatest ultramarathon |
Altitude & Heat Adjustments
Heat penalty: ~1.5% per 5°C above 15°C | Humidity adds up to 0.5% additional above 60%
Race Strategy Planner
| Half | Pace | Half Time |
|---|---|---|
| First half | 3:17/km | 2:26:15 |
| Second half | 3:27/km | 2:33:45 |
| Total | 3:22/km | 5:00:00 |
Comrades Marathon Checkpoint Guide (Down Run)
| Checkpoint | km | Your ETA | Cutoff | Buffer |
|---|---|---|---|---|
| Start (Durban) | 0 | 0:00:00 | 0:00:00 | 0m |
| Pinetown | 13 | 0:43:49 | 1:30:00 | +46m |
| Hillcrest | 22 | 1:14:09 | 2:45:00 | +91m |
| Camperdown | 40 | 2:14:50 | 5:00:00 | +165m |
| Drummond | 50 | 2:48:32 | 6:15:00 | +206m |
| Inchanga | 60 | 3:22:15 | 7:30:00 | +248m |
| Cato Ridge | 67 | 3:45:51 | 8:30:00 | +284m |
| PMB Finish | 89 | 5:00:00 | 12:00:00 | +420m |
Checkpoint cutoff times are approximate. Always verify official Comrades Marathon cutoffs for the current year. Finish before the gun in 12 hours.