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Running Pace Calculator
Pace, time, distance, and race-time predictions — switch the mode and we'll solve for whatever's missing.
Race-time predictor
Holding the pace above constant, here's roughly what your race times would look like. Real performance depends on training, terrain, and fatigue — these are flat, even-pace estimates.
| Race | Distance | Predicted time |
|---|---|---|
| 5K | 5.0 km / 3.11 mi | — |
| 10K | 10.0 km / 6.21 mi | — |
| Half-marathon | 21.10 km / 13.11 mi | — |
| Marathon | 42.20 km / 26.22 mi | — |
Linear extrapolation from your current pace. Use Riegel or VDOT for race-specific predictions.
Pace vs. speed
Speed answers "how far per hour?" and goes up when you're faster. Pace answers "how long per kilometer (or mile)?" and goes down when you're faster. Runners think in pace because every workout has a target like "4:30/km" or "8:00/mi" — it makes splits, intervals, and tempo runs easy to plan and check on the watch.
How to use it
Three modes, one form.
- Pick the mode — Pace (from distance + time), Time (from distance + pace), or Distance (from time + pace).
- Fill in the inputs that show up. Distance can be km or miles; time is hours/minutes/seconds.
- Read the result and the breakdown — pace per km and per mile, plus speed in km/h and mph. The race-time table updates automatically.
The formula
Pace is just time divided by distance. Speed is the inverse: distance divided by time, scaled to an hour.
pace = time ÷ distance · speed = distance ÷ time
Training pace zones
Most plans split work into intensity zones. Approximate percent of max heart rate is shown — VO2max work is short and hard, easy runs are most of your weekly volume.
| Zone | Effort (% HRmax) | Purpose |
|---|---|---|
| Easy / aerobic | 60–70% | Build aerobic base, recover between hard sessions. |
| Marathon | 75–84% | Sustainable for ~2–4 hours. Race pace for marathoners. |
| Tempo | 83–88% | "Comfortably hard" — improves lactate clearance. |
| Threshold | 88–92% | Holdable for ~30–60 min. Raises lactate threshold. |
| VO2max | 95–100% | Short, hard intervals. Lifts top-end aerobic capacity. |
Smart pacing tips
Most runners blow up by going out too hard. A few rules that almost always pay off:
- Run easy days actually easy — slow enough to chat in full sentences.
- Aim for even or negative splits in races: same pace, or slightly faster, in the second half.
- Heat, hills, and humidity all add seconds per km — adjust the target, don't muscle through.
- Use 80/20: ~80% of weekly volume easy, ~20% at threshold/VO2max.