Pace Calculator
Running pace, finish time, and speed — with per-distance splits.
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Pace, time, and distance are three views of the same relationship, so entering any two gives you the third. Enter a distance and a finish time to get your pace; a distance and a target pace to get your finish time; or a time and a pace to see how far that takes you.
Every result also shows speed (km/h or mph) and a splits table — your cumulative time at each kilometre or mile, which is how a race is actually paced. Quick-select buttons cover 5K, 10K, half marathon, and marathon, and you can switch between kilometres and miles at any point.
📖 Read the guide: What Pace Do You Need for a Sub-2-Hour Half Marathon?
Formula
Pace
pace = time ÷ distance
time is the total elapsed time and distance is the total distance covered, both in the units you selected. The result is the time to cover one unit, shown as minutes:seconds per kilometre or mile. Example: 50 minutes over 10 km → 3,000 s ÷ 10 = 300 s = 5:00/km.
Finish time
time = pace × distance
The same relationship rearranged. Example: a marathon (42.195 km) at 5:00/km → 300 s × 42.195 = 12,658.5 s = 3:30:58.
Speed
speed = distance ÷ time
The same information expressed as distance per hour rather than time per distance. A 5:00/km pace is 12 km/h, because 60 minutes ÷ 5 minutes per km = 12.
Examples
| Example | Input | Result |
|---|---|---|
| Pace | 10 km in 50:00 | 5:00/km · 12 km/h |
| Time | Marathon at 5:00/km | 3:30:58 |
| Distance | 60:00 at 5:00/km | 12 km |
| Sub-2 half | 21.0975 km in 1:59:59 | 5:41/km |
| 5K target | 5 km at 4:30/km | 0:22:30 |
How to use the pace calculator
- 1Choose a mode: Pace, Time, or Distance.
- 2Enter the two known values (use the quick-select buttons for race distances).
- 3Read your pace, speed, finish time, and the splits table.
What running pace means
Pace is how long it takes you to cover one unit of distance — for example, 5:00 per kilometer means each kilometer takes five minutes. It's the most useful number for runners because it's directly comparable across distances and easy to hold during a race. Speed (km/h or mph) is the same information expressed as distance per hour.
Planning a race with splits
The splits table shows your cumulative time at each kilometer or mile, which is how you pace a race in practice. To run an even race, aim to hit each split at the same pace; many runners plan a slight negative split (running the second half a touch faster). Enter a goal finish time in Time mode to see the pace and splits you'd need.
Assumptions and limitations
- This is even-pace arithmetic. It assumes you cover every kilometre at the same rate, so the splits are a plan rather than a prediction — real races vary with hills, wind, fatigue, and crowding.
- Pace is not a fitness model. It cannot estimate what you are capable of, predict a race result from a training run, or convert a time at one distance into an equivalent time at another; those need a physiological model this calculator does not implement.
- Pace is displayed to whole seconds and speed to two decimal places. A rounded pace multiplied back out by hand may differ from the finish time shown by a second or two — the calculation keeps full precision internally.
- Splits are listed for each whole unit, with a final partial split where the distance is not a whole number. Above 100 whole units the per-unit list is capped to keep the table readable.
- Zero or negative distances, times, and paces return no result rather than an error value, since none of them describe a run.
How this calculation is tested
The math for this tool lives in lib/calc-engine/pace-calculator.ts — a plain function with no interface code around it. The page you are using and the automated tests call that same function, so the tests check the behaviour you actually get.
The tests check:
- pace from distance and time (10 km in 50 minutes = 5:00/km)
- finish time from pace (marathon at 5:00/km = 3:30:58)
- distance from time and pace (60 minutes at 5:00/km = 12 km)
- per-unit split generation
- invalid inputs returning no result
Automated tests reduce implementation errors — they confirm the code computes the formula it is supposed to. They are not a professional review, and they cannot tell you whether this formula is the right one for your situation. More detail on how calculations are built and tested.
Sources
- World Athletics — Competition Rules (Book C2.1), road race distances
The standard distances used by the quick-select buttons — half marathon 21.0975 km and marathon 42.195 km — are fixed by World Athletics rather than derived arithmetically.
Frequently asked questions
What is running pace?
Pace is the time it takes to cover one unit of distance, shown as minutes:seconds per kilometer or mile. A 5:00/km pace means each kilometer takes five minutes.
How do I calculate my pace per km?
Divide your total time by the distance. For example, 50 minutes (3,000 seconds) over 10 km is 300 seconds per km, or a 5:00/km pace. The Pace mode does this for you.
What is a good pace for a 5K?
It depends on fitness and goals. A beginner might run 7:00–8:00/km, a recreational runner around 5:30–6:30/km, and a competitive runner under 4:00/km. Use the calculator to set realistic splits for your target time.
How do I convert pace to speed?
Speed is distance ÷ time. A 5:00/km pace is 12 km/h (60 minutes ÷ 5 minutes per km). The calculator shows both pace and speed for every result.
What pace do I need to run a sub-2-hour half marathon?
A half marathon is 21.0975 km, so under 2 hours requires faster than about 5:41/km (or roughly 9:09/mile). Use Time mode with a 1:59:59 goal to see the exact pace and splits.
How do I calculate my marathon finish time?
Enter the marathon distance (42.195 km) and your goal pace in Time mode. For example, 5:00/km gives a finish time of about 3:30:58.
Embed this calculator
Add the Pace Calculator to your own website — free. Copy and paste this snippet:
<iframe src="https://numvella.com/embed/pace-calculator" width="100%" height="460" style="border:1px solid #e2e8f0;border-radius:12px" title="Pace Calculator — Numvella" loading="lazy"></iframe>