The Running Pace Calculator turns a distance and a time into your pace per kilometre and per mile, your average speed, and projected finish times for the standard race distances. Whether you’re checking a training run or planning race-day strategy, it gives instant answers in your browser.
How pace is calculated
Pace is total time divided by distance:
pace = time ÷ distance
The tool converts your distance into both kilometres and miles, so you get pace per km and per mile, plus average speed in km/h and mph.
Race-time projections
From your current pace it projects finish times for 5K, 10K, half marathon (21.0975 km) and full marathon (42.195 km), assuming you hold that pace throughout.
| Distance | Based on |
|---|---|
| 5K | your pace × 5 km |
| 10K | your pace × 10 km |
| Half marathon | your pace × 21.0975 km |
| Marathon | your pace × 42.195 km |
Most runners slow over longer distances, so treat a marathon projected from a 5K pace as an optimistic ceiling, not a guarantee.
Illustrative pace reference
To give a sense of where different paces land, here are common recreational benchmarks. These are illustrative examples only — individual performance varies widely:
| Pace per km | 5K finish time | 10K finish time | Marathon finish time |
|---|---|---|---|
| 4:00 min/km | 20:00 | 40:00 | ~2:48 |
| 5:00 min/km | 25:00 | 50:00 | ~3:31 |
| 6:00 min/km | 30:00 | 1:00:00 | ~4:13 |
| 7:00 min/km | 35:00 | 1:10:00 | ~4:55 |
| 8:00 min/km | 40:00 | 1:20:00 | ~5:37 |
Why projected race times can be optimistic
The projections assume a constant pace across the full distance, which is how the arithmetic works but rarely how running does. The main factors that slow you over longer distances:
- Glycogen depletion. At around 32–35 km in a marathon (“the wall”), glycogen stores can run low, forcing the body to rely more on fat — a slower fuel. Proper fuelling strategy mitigates but does not eliminate this.
- Muscle fatigue. Running economy (oxygen cost per km) increases with fatigue, so you work harder for the same speed.
- Heat and conditions. Longer races accumulate more exposure to heat, wind, and terrain variation.
A common rule of thumb is that marathon pace should be roughly 45–90 seconds per km slower than 10K pace for most recreational runners. Use the projection from a long training run pace rather than a 5K PB for the most realistic marathon estimate.
Common uses for this calculator
- Checking a training run: enter your GPS distance and time after a run to see your average pace and compare it to your target training zone.
- Race-day pacing: work backwards — enter your goal time and race distance to find the pace you need to hold per kilometre.
- Converting between units: if your GPS watch shows pace per mile but your race is measured in kilometres, the converter gives both instantly.
Everything is calculated locally in your browser.