“What pace do I need to run a sub-2-hour half marathon?” is a question every runner eventually asks. Our pace calculator works from any recent run’s distance and time to compute your pace, speed, and predicted finish times across the standard race distances.
Pace vs speed
Pace is time per unit distance (minutes per km or mile) — what most runners think in during a race. Speed is distance per unit time (km/h or mph) — more common for cycling. The calculator shows both from a single input.
Example
5 km in 25:00:
- Pace: 5:00/km
- Speed: 12.00 km/h
Race predictions
Using that same pace, the calculator projects finish times for standard distances:
- 5K: 25:00
- 10K: 50:00
- Half marathon (21.0975 km): 1:45:29
- Marathon (42.195 km): 3:30:59
An important caveat on the predictions
These predictions assume you could hold your exact training pace across the entire race distance. In practice, pace naturally degrades somewhat as distance increases — a pace that feels comfortable for 5K is rarely sustainable unchanged for a full marathon. Treat longer-distance predictions as an optimistic ceiling, not a guarantee, and adjust your race-day goal pace downward accordingly, especially for marathon distance.
Why the half and full marathon distances look odd
21.0975 km and 42.195 km come from the historically standardized Olympic marathon distance — not a rounding artifact in this calculator.