Race Time Predictor (Riegel Formula)
Predicted finish time and pace for a half marathon, marathon or any distance from a recent race result, using Riegel's formula.
Results
Predicted time — hours
1
h
Predicted time — minutes
50
min
Predicted time — seconds
19
s
Pace — minutes per km
5
min
Pace — seconds
14
s
Speed
11.47
km/h
The dashed line marks the value you entered.
What this tool does
Peter Riegel noticed in the 1970s that across running, swimming and cycling the time grows a little faster than the distance — by the power 1.06 — because you cannot hold the same pace for longer. So a 50-minute 10 km suggests about 1 h 50 min for a half marathon. The prediction is best between similar distances and assumes you have trained for the longer one; for the marathon it is often optimistic for runners without enough long runs, and a slightly higher exponent such as 1.07–1.08 can be more realistic.
Formula
T₂ = T₁ × (D₂ ÷ D₁)^1.06
Variables
| Symbol | Meaning | Unit |
|---|---|---|
d1 | Distance of a race you have run | km |
hh | Your time — hours | h |
mm | Your time — minutes | min |
ss | Your time — seconds | s |
d2 | Distance to predict | km |
ex | Fatigue exponent | — |
H | Predicted time — hours | h |
M | Predicted time — minutes | min |
S | Predicted time — seconds | s |
PM | Pace — minutes per km | min |
PS | Pace — seconds | s |
SP | Speed | km/h |
Worked example
- Distance of a race you have run10 km
- Your time — hours0 h
- Your time — minutes50 min
- Your time — seconds0 s
- Distance to predict21.0975 km
- Fatigue exponent1.06
- Predicted time — hours1 h
- Predicted time — minutes50 min
- Predicted time — seconds19 s
- Pace — minutes per km5 min
- Pace — seconds14 s
- Speed11.47 km/h
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.