5K Pace Calculator
A 5K pace calculator with a bonus: enter one honest 5K time trial and get your current pace plus Riegel-formula predictions for 10K, half marathon and marathon. The 5K is the standard fitness benchmark — short enough to repeat monthly, long enough to mean something.
Result
| Your 5K pace |
Riegel predictions (equivalent performances)
Formula & source
Pace = time ÷ distance
Source: Pete Riegel's formula (Runner's World, 1977; refined 1981), fitted on world-record performances across distances — the most-cited race prediction equation in running. Exponent 1.06 captures that pace fades slightly with distance. Unique to this page: predictions are computed live from your trial instead of a static table, so any 5K time works.
Worked example (you can verify by hand)
Input: 5K in 25:00 (1500 s).
- 10K: 1500 × (10/5)1.06 = 1500 × 2.0849 = 3127 s = 52:07
- Half: 1500 × (21.0975/5)1.06 = 1500 × 4.600 = 6900 s = 1:55:00
- Marathon: 1500 × (42.195/5)1.06 = 1500 × 9.587 = 14381 s = 3:59:41
Expected output: 10K 52:07 · half 1:55:00 · marathon 3:59:41.
Limitations — what this cannot do
- GPS watches and phone apps typically err by 1–3% on distance; a track-measured time trial is the honest input.
- Hills, heat, altitude and wind change real-world pace — charts assume flat, sea-level, calm conditions.
- Predictions assume similar training and conditions; they are estimates, not guarantees.
- Riegel assumes equivalent training for the longer distance — a 5K specialist without long runs will miss the marathon prediction.
Disclaimer: Estimates for training planning only, not medical advice. Consult a professional.
FAQ
How accurate is the Riegel formula?
Within a few percent for trained runners racing equivalent distances. It breaks down when comparing very short to very long races without matching training.
How often should I run a 5K time trial?
Every 4–8 weeks in base training. Same course, similar conditions, rested legs — otherwise you are measuring noise, not fitness.
Why does my marathon prediction look too fast?
The formula assumes you actually train for the marathon (long runs, fueling). Without that aerobic base, expect 5–10% slower.
5K pace vs easy pace — how far apart?
Easy running is typically 60–90 s/km slower than 5K pace. If your 5K pace is 5:00/km, easy runs belong around 6:00–6:30/km.