What This Pace Calculator Does
Running math is one relationship wearing three hats:
- Find pace: "I ran 10K in 52:30 — what was my pace?" → 5:15/km
- Find time: "What does a marathon take at 5:40/km?" → 3:59:05
- Find distance: "45 minutes at 6:00/km covers…?" → 7.5 km
Give any two, get the third — in per-kilometer or per-mile units — plus a split table showing what each kilometer/mile marker should read on your watch. That table is the difference between racing a plan and improvising one.
Pace Reference Tables
Common race finish times by pace
| Pace/km | 5K | 10K | Half | Marathon |
|---|---|---|---|---|
| 4:00 | 20:00 | 40:00 | 1:24:23 | 2:48:46 |
| 5:00 | 25:00 | 50:00 | 1:45:29 | 3:30:58 |
| 6:00 | 30:00 | 1:00:00 | 2:06:35 | 4:13:10 |
| 7:00 | 35:00 | 1:10:00 | 2:27:41 | 4:55:21 |
Handy conversion: pace/mile ≈ pace/km × 1.609 (5:00/km ≈ 8:03/mile). Speed in km/h = 60 ÷ pace-in-minutes.
Predicting Race Times From a Recent Result
You can't hold 5K pace for a marathon — performance decays predictably with distance. The classic Riegel formula:
Example: a 25:00 5K predicts 10K ≈ 25 × 21.06 ≈ 52:05 (not 50:00 — the extra 2 minutes is the distance tax). Predictions assume appropriate training for the target distance; a 5K PR predicts a marathon only if you've built the endurance base.
Training Paces: Why Easy Days Should Be Easy
Most training plans define paces relative to your current race ability. Anchored to a recent 5K:
| Zone | Rough pace vs 5K | Purpose |
|---|---|---|
| Easy / recovery | +1:15 to +2:00 per km | Aerobic base — the bulk of weekly mileage |
| Marathon pace | +35 to +50s | Race-specific endurance |
| Threshold/tempo | +10 to +20s | Raise the "comfortably hard" ceiling |
| Interval (VO₂) | at or slightly faster than 5K | Top-end aerobic power |
The most common training error is running easy days too fast — compute your easy range above and respect it; the speed comes from the hard days being genuinely hard.
Race-Day Splits: Even, Negative, and the Banked-Time Trap
- Even splits (same pace throughout) — the statistically strongest strategy for most runners; the split table above is exactly this plan.
- Negative splits (second half faster) — how most world records are run; start 5–10s/km conservative, finish strong.
- "Banking time" (fast early) — feels prudent, fails predictably: minutes gained early cost multiples later. Physiology doesn't refund enthusiasm.
Adjust expectations for heat (+10–30s/km when hot/humid), hills, and crowded starts — a plan that ignores conditions isn't a plan.
The Bottom Line
Every good race is arithmetic executed calmly: a target time, the pace it implies, and the splits that confirm you're on it. Compute your numbers above, write the key splits on your arm if you have to, and let even pacing do what heroics can't. For the calorie side of training, see the Calorie Calculator.