Pace, speed, and splits in plain English
Pace is time per distance — minutes per kilometre — while speed is distance per hour. Convert instantly: km/h equals 60 ÷ pace, so 5:00/km is exactly 12 km/h and 6:00/km is 10 km/h. A treadmill at 11 km/h means 60 ÷ 11 = 5:27 per km.
Race times fall straight out: 5 km at 5:00/km is 25:00, 10 km is 50:00, a half marathon (21.0975 km) 1:45:29, a marathon (42.195 km) 3:30:59 — if anyone could hold it that long, which the predictor section corrects for. Splits apply pace per kilometre: even 5:00s, or 5:10s early and 4:50s late for a negative split.
- Speed = 60 ÷ pace; 5:00/km is 12 km/h, 6:00/km is 10 km/h
- Even splits suit beginners; slight negative splits suit racers
- Program a pace band on your watch before race day
Pace chart: what each pace gives you
At 4:30/km: 5K in 22:30, 10K in 45:00, half in ~1:34:56. At 5:00/km: 25:00, 50:00, ~1:45:29. At 5:30/km: 27:30, 55:00, ~1:56:02. At 6:00/km — a proud beginner milestone — 30:00, 60:00, ~2:06:35. At 6:30/km: 32:30, 65:00, ~2:17:08.
Mile runners divide by 1.609: 5:00/km is 8:03 per mile. Treadmill runners should set 1% incline to mimic outdoor effort. Base targets on a recent hard 5K time trial — the matching row gives honest 10K and half-marathon goals, not fantasy ones.
- 5:00/km → 25:00 / 50:00 / ~1:45 half; 6:00/km → 30:00 / 60:00 / ~2:07 half
- Per-mile pace ÷ 1.609 gives per-km pace
- Target from a recent time trial, never from wishful thinking
Predict your race time from any result
Longer races run slower per kilometre — the Riegel formula captures it: predicted time = known time × (new distance ÷ old distance)^1.06. A 25:00 5K predicts 10K as 25 × 2^1.06 = 25 × 2.085 = ~52:08, honestly slower than doubling.
The same 5K predicts a half of 25 × (21.0975 ÷ 5)^1.06 = 25 × 4.60 = 1:55 flat, and a marathon of 25 × 9.59 ≈ just under 4:00. A 30:00 5K converts to ~62:30 and ~2:18. Treat predictions as centre lines with a ±3–5% band for hills, heat, and race-day adrenaline.
- Riegel: new time = old time × (new km ÷ old km)^1.06
- 25:00 5K → ~52:08 / ~1:55 half / ~4:00 marathon
- 30:00 5K → ~62:30 10K and ~2:18 half
Train at five paces, not one
A 25:00 5K runner (5:00/km race pace) needs five gears. Easy runs at 5:50–6:20/km — conversational — build the base and should be 70–80% of weekly kilometres. Tempo at 5:10–5:20/km for 20–30 minutes raises the lactate threshold. Intervals like 6 × 800 m at 4:40–4:50/km lift top speed.
The long run is the fifth gear: 90+ minutes starting near 6:10/km, finishing the last 20 minutes near 5:30/km. One long run plus one tempo or interval session, surrounded by easy kilometres, is the whole philosophy behind most sub-2-hour halves. Raise weekly distance 10% at most, with a lighter fourth week.
- 80% easy, 20% hard — the ratio behind most half-marathon breakthroughs
- Easy 5:50–6:20, tempo 5:10–5:20, intervals ~4:40–4:50 (for 25:00 5K)
- Never add distance and speed in the same week
Fuel, calories, and heart rate at pace
Running costs ~1 kcal per kg per km regardless of pace: a 70 kg runner spends ~70 kcal per kilometre, so 10K is ~700 kcal and a half ~1,475 kcal. Three weekly 5Ks burn ~1,050 kcal total — less than one large restaurant meal — so pair running with a measured diet for fat loss.
Heart-rate zones keep effort honest when pace lies in heat or hills. Estimate max as 220 − age (a 35-year-old: ~185 bpm): easy at 60–70%, tempo 80–87%, intervals above 90%. Heat alone adds 10–15 bpm, so slow down without guilt. Chest pain, fainting, or known heart disease means medical clearance before racing or intervals.
- Budget ~1 kcal per kg per km: 70 kg × 10K ≈ 700 kcal
- Easy 60–70% of max HR; tempo 80–87%; intervals 90%+
- Heat adds 10–15 bpm — hold the zone, not the pace
5 pacing mistakes runners repeat
The adrenaline start: kilometre one at 4:30 against a 5:00 plan, then a long fade finishing slower than even pacing would have. Let strangers sprint away; collect them by kilometre four. Second, racing every training run — constant 90% effort plateaus fitness and invites injury within two months.
Third, skipping the 10-minute jog-and-leg-swing warm-up, then straining a calf on the first interval. Fourth, copying elite mileage: a 25:00 engine needs 25–35 km a week, not 100. Fifth, debuting shoes or gels on race day. Nothing new on race day except courage.
- Start 5–10 seconds slower than target for kilometre one
- Keep easy days genuinely easy — daily racing injures
- Test shoes, gels, and breakfast on long runs only
Running pace questions, answered
What is a good 5K? Under 35:00 is a fine first goal, 30:00 solid, 25:00 genuinely quick, sub-22:30 turns heads locally. Pace or heart rate? Pace on flat cool days, heart rate in heat, hills, and comebacks — when they disagree, trust effort over the watch.
To break 30:00, run 20–25 km a week with one interval session (5 × 1 km at 5:40/km, 2-minute jogs) plus a 45–60 minute long run, for eight weeks, then time-trial. Predictors hold within ~3% between adjacent distances and ~5% across leaps — if the mileage matches the distance.
- Beginner ladder: 35:00 → 30:00 → 25:00 → sub-22:30
- Break 30:00 with weekly intervals plus a long run, eight weeks
- Predictions assume matching training — mileage first