Core answer: Pace (min/km) = total minutes ÷ distance; speed (km/h) = 60 ÷ pace. A 5:00/km pace = 12 km/h; a 10 km run in 50 min means averaging exactly 5:00/km. Finish-time formula: time = pace × distance — at 6:00/km a half marathon (21.0975 km) takes 2:06:35. Treadmill conversion: 12 km/h = 5:00/km, 10 km/h = 6:00/km, 8.5 km/h ≈ 7:04/km.
The pace-speed-finish triangle
| Pace (min/km) | Speed (km/h) | 5K | 10K | Half | Full |
|---|---|---|---|---|---|
| 4:00 | 15.0 | 20:00 | 40:00 | 1:24:23 | 2:48:47 |
| 5:00 | 12.0 | 25:00 | 50:00 | 1:45:29 | 3:30:59 |
| 6:00 | 10.0 | 30:00 | 1:00:00 | 2:06:35 | 4:13:10 |
| 7:00 | 8.6 | 35:00 | 1:10:00 | 2:27:41 | 4:55:22 |
| 8:00 | 7.5 | 40:00 | 1:20:00 | 2:48:47 | 5:37:34 |
Worked examples
Example 1 — Goal pacing. Target: sub-2 half marathon. Required pace = 120 min ÷ 21.0975 = 5:41/km. Training should make 5:35 feel controlled, leaving race-day margin.
Example 2 — Negative split strategy. First 5K at goal +10 s/km, middle at goal, last 5K at goal −10 s: the same average feels dramatically easier and passes crowds of positive-splitters after 15 km.
Example 3 — Treadmill truth. Treadmill 12 km/h ≈ outdoor 5:00/km but easier (no wind, belt assist): add 1% incline to approximate outdoor effort.
Example 4 — The 80/20 rule. 80% of weekly volume at conversational pace (you can speak full sentences, ~1.5–2 min/km slower than race pace), 20% faster. Running every day "kind of hard" is the most common plateau cause.
Heart-rate-based pacing (zone 2)
Zone 2 ≈ 60–70% of max HR (rough: 180 − age). For a 35-year-old: ~130–140 bpm. At this pace fat burning peaks and recovery cost is minimal — most beginners run their easy days too fast and their hard days too slow, the "black hole" of training.
Common mistakes and myths
- GPS worship — urban GPS drifts ±3–5%; instant pace is noise, lap pace is signal.
- Treadmill = outdoor equivalence — see the 1% rule; also treadmills report belt speed, which calibration errors can skew ±5%.
- Ignoring heat and hills — +10 °C costs ~1.5–3% pace; a 1% grade costs roughly 12–15 s/km; adjust goals on brutal days.
- "Slower means no benefit" — zone-2 volume builds the aerobic engine that race pace draws from; elites run 80% of mileage slowly.
- Km vs mile confusion — a 7:00/mile pace = 4:21/km (much faster); US plans quote miles, Chinese runners think in km — convert before copying workouts.