Running Pace Calculator
Type a goal time + distance to see your pace. Or a pace + distance to see the finish time. Or a recent race result to predict a different distance. Splits table updates as you type, and the URL is the bookmarkable scenario.
Equivalent race times
| Race | Predicted time | Pace /km |
|---|
Training paces (estimates)
| Zone | Pace /km |
|---|
Rule-of-thumb ranges, not a coaching plan — these approximate common training-pace tables (McMillan / Daniels-style), derived from your Riegel-equivalent race times.
Show per-km splits
| # | km | Split | Cumulative |
|---|
What this calculator does
- Find time — distance + pace → total time and per-km/mile splits.
- Find pace — distance + goal time → pace, plus speed in km/h and mph.
- Find distance — pace + total time → how far you'd run.
- Predict race — recent race result + target distance → predicted finish time, using the Riegel formula. Also shows equivalent times for 5K / 10K / half / marathon and estimated training paces.
How it works, step by step
Pace, time, and distance are linked, so any two give you the third. Pick the mode for the one you're missing. Enter a distance in km or miles, or pick a standard race. Enter times as hours, minutes, and seconds.
The calculator converts everything to seconds and kilometres, does the arithmetic, and converts back. One mile is exactly 1.609344 km, so pace per mile is always pace per km × 1.609344. That's why both are shown side by side. The splits table repeats your pace at every km or mile marker. For predictions, enter a recent race result and a target distance, and the Riegel formula scales the time. It all runs in your browser, and the URL keeps your inputs so you can come back to them.
The math
Three of the modes are pure division: pace = time / distance,
time = pace × distance, distance = time / pace.
The race-time predictor uses Peter Riegel's 1981 formula:
T2 = T1 × (D2 / D1)1.06
where T1, D1 are the reference race time and
distance, and D2 is the target distance. The 1.06 exponent
is empirical — it captures the typical fall-off in pace as distance grows.
Riegel is an estimate. It's usually closest between nearby distances
and least reliable when you predict a marathon from a 5K.
Worked examples
A 25-minute 5K: what pace is that?
pace = time ÷ distance
= 25:00 ÷ 5 km
= 1,500 s ÷ 5 = 300 s/km → 5:00 per km
per mile = 300 s × 1.609344 = 482.8 s → about 8:03 per mile
speed = 5 km ÷ (25/60) h = 12.0 km/h (about 7.46 mph)The km splits are simply 5:00, 10:00, 15:00, 20:00, and 25:00. Hit each marker on time and you finish in 25:00.
Predicting a half marathon from a 50-minute 10K
T2 = T1 × (D2 ÷ D1)^1.06
= 3,000 s × (21.0975 ÷ 10)^1.06
= 3,000 s × 2.2064
≈ 6,619 s → 1:50:19That works out to about 5:14 per km, or 8:25 per mile. The ratio here is about 2.1×, well inside the range where Riegel tends to hold up. For where the formula breaks down, see the race-time prediction guide.
Sharing a scenario
Every input is encoded in the URL hash. Copy the URL and the recipient sees the same calculator state. "Share link" copies it; the browser also keeps it as you edit, so you can bookmark mid-flight.
Tips
- Negative splits usually beat even splits in races over 10K. Target a 5–10 second per km slower split for the first 30%, then make it up.
- Round numbers help. "5:00 / km" is easier to hold mentally than "4:53 / km" — pick a slightly easier target if you're racing on feel.
- Long-run paces are slower than race paces. A common rule: long-run pace ≈ marathon goal pace + 30–60 sec/km.
- Watch the pace decay if you're using Riegel for a marathon prediction from a 5K. The 5K → marathon prediction is the most error-prone case; double-check against a half-marathon time if you have one.
What this calculator does not do
- Heart rate or VO2max math — pace only.
- Elevation profile — assumes flat course.
- Negative-split planner — this page doesn't plan negative splits.
- Pacing for cycling / swimming — different physics, different formulas.
Related
- Health hub — BMI, BMR, TDEE, and macro calculators for the rest of training.
FAQ
Is anything I enter sent to a server?
No. All math runs in your browser — open DevTools → Network and confirm. The URL hash carries your inputs so you can share a link, but that hash is only sent to your own browser.
How does the race-time predictor work?
It uses the Riegel formula: T2 = T1 × (D2/D1)^1.06. Plug in a recent race time and distance, then a target distance — it predicts the new finish time. The exponent 1.06 reflects that pace usually drops slightly as race distance grows. Riegel is a useful estimate for distances within ~3× of your reference race; further out it tends to optimistic.
What are the 'equivalent race times'?
The same Riegel formula applied from your entered race to the four standard distances — 5K, 10K, half marathon, marathon — each with its predicted pace in your chosen unit. They answer "what is this performance worth at other distances?" The further a distance is from your reference race, the rougher the estimate; 5K → marathon is the most optimistic case.
How are training paces estimated?
They're rule-of-thumb offsets from your Riegel-equivalent race paces, in the spirit of McMillan- / Daniels-style training-pace tables: easy/long ≈ marathon pace + 45–90 s/mi (+28–56 s/km), marathon = marathon pace, threshold/tempo ≈ half-marathon pace − ~10 s/mi (−6 s/km), interval/VO₂ ≈ 5K pace, and recovery = easy + 30 s and slower. These are honest approximations, not a coaching plan — a structured system (Daniels' VDOT, McMillan's calculator) accounts for more variables, and any prescribed pace should yield to how you actually feel on the day.
Can I switch between km and miles?
Yes — the unit toggle on the distance row applies to that input. The pace-per-km / pace-per-mi outputs are always shown, so you can read either.
What does the splits table show?
Even pacing splits — the time you'd hit at each km (or mile) marker if you held a perfectly flat pace. Useful for race-day planning. For negative-split pacing, target a slightly slower split for the first half and a faster one for the second.
What about elevation and terrain?
The calculator assumes flat, even pacing. For hilly courses, expect ~10–20 seconds per km slower on uphill kilometers and ~5–10 seconds per km faster on downhill. The Riegel predictor implicitly assumes the target race has similar terrain to your reference race.
How far is a half marathon and a marathon in miles?
A half marathon is 21.0975 km, about 13.11 miles. A marathon is 42.195 km, about 26.22 miles, usually rounded to 13.1 and 26.2.
How do I convert pace per km to pace per mile?
Multiply the pace per km by 1.609344. For example, 5:30 per km is about 8:51 per mile. To go the other way, divide by 1.609344.
What pace do I need for a sub-2-hour half or a sub-4-hour marathon?
Both work out to the same pace, because a marathon is exactly twice a half: about 5:41 per km, or 9:09 per mile. To finish under the target, run slightly faster than that on average.
What's the difference between pace and speed?
Pace is time per distance, such as 5:00 per km. Speed is distance per time, such as 12 km/h. They describe the same effort: 60 divided by your pace in minutes gives your speed.
Why doesn't my GPS watch distance match the race distance?
Race courses are measured along the shortest possible line, and most runners cover a little more by weaving and taking wider turns. GPS readings add some error too, so the watch's average pace can look faster than your official pace.
Should I enter my chip time or gun time?
Use chip time for pace and predictions. It measures from when you crossed the start mat to the finish, so it reflects your actual running time.