Pace Calculator: How It Works
Pace is time per unit distance; speed is distance per unit time. Runners plan in pace because it is what you can actually hold and feel. This calculator converts between pace, speed, distance and finish time, and this page covers how to pick a pace you can sustain.
The conversions
Pace = time ÷ distance · Speed = distance ÷ time
To convert between them: km/h = 60 ÷ (minutes per km). A 5:00/km pace is 12 km/h. A 6:00/km pace is 10 km/h.
| Pace /km | Pace /mile | km/h | 5 km | 10 km | Half | Marathon |
|---|---|---|---|---|---|---|
| 4:00 | 6:26 | 15.0 | 20:00 | 40:00 | 1:24:24 | 2:48:48 |
| 4:30 | 7:15 | 13.3 | 22:30 | 45:00 | 1:34:57 | 3:09:54 |
| 5:00 | 8:03 | 12.0 | 25:00 | 50:00 | 1:45:30 | 3:31:00 |
| 5:30 | 8:51 | 10.9 | 27:30 | 55:00 | 1:56:03 | 3:52:06 |
| 6:00 | 9:39 | 10.0 | 30:00 | 1:00:00 | 2:06:36 | 4:13:12 |
| 7:00 | 11:16 | 8.6 | 35:00 | 1:10:00 | 2:27:42 | 4:55:24 |
Predicting a longer race from a shorter one
Riegel's formula is the standard approach:
T₂ = T₁ × (D₂ ÷ D₁)1.06
A 22-minute 5 km predicts a 10 km of 22 × 21.06 ≈ 45:50, and a marathon of about 3:26. The exponent 1.06 encodes the fact that pace degrades with distance — you cannot hold 5 km pace for a marathon.
The prediction assumes appropriate training for the longer distance. Extrapolating a marathon time from a 5 km when your longest run is 10 km will produce a number and not a result.
Training paces
| Session | Relative to 5 km pace | Purpose |
|---|---|---|
| Easy / recovery | +90 to +120 s per km | Aerobic base; most of your weekly volume |
| Long run | +60 to +90 s per km | Endurance, fat metabolism |
| Tempo / threshold | +20 to +30 s per km | Raises the pace you can hold |
| Interval | −5 to −15 s per km | Speed and running economy |
The most common error in amateur training is running easy days too fast. Easy runs are meant to be genuinely conversational; running them at moderate effort accumulates fatigue without the stimulus of a hard session — the worst of both.
Even, negative and positive splits
Running the second half of a race faster than the first is a negative split, and it is how most personal bests are set. Starting too fast depletes glycogen early and raises lactate before the body has settled, which is why a positive split usually costs more time in the closing kilometres than it gained in the opening ones. Aim to run the first few kilometres slightly slower than goal pace.
What changes your pace on the day
- Heat. Above roughly 15 °C, expect to slow — often 2–4% for every 5 °C above that, more with humidity.
- Elevation. A rough guide is 8–10 seconds per kilometre lost for every 10 m of climb, only partly recovered on the descent.
- Altitude. Noticeable above about 1,200 m until acclimatised.
- Surface. Trail and sand are substantially slower than road at the same effort.