Pace Calculator
Compute running pace, finish time, or distance from any two of them. Presets for 5K, 10K, half, and marathon.
Pace
5:00 /km
Time
50:00
Avg speed
12.00 km/h
Linear projection — actual race times for longer distances usually run slower than this from fatigue.
How to use
- Pick which value you want computed: pace, time, or distance.
- Fill in the remaining two fields.
- Read pace, time, and average speed in the output cards. The computed field is highlighted.
About this tool
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Give any two of pace, time and distance and the third is worked out for you, in metric or imperial, with the equivalent speed shown alongside. Race presets cover 5K, 10K, half marathon and marathon, and they use the official distances rather than the round numbers people quote — 21.0975 km and 42.195 km. That precision is not pedantry: planning a marathon at 5:00 per kilometre against a flat 42 km makes your predicted finish almost a full minute optimistic, which is the sort of error that turns a target into a disappointment in the last two hundred metres. Useful for setting a goal time, checking what a training pace works out to per mile, or converting a treadmill speed into the pace you actually think in.
Frequently asked questions
Why does my pace look slower in imperial?
A mile is longer than a kilometer, so the same speed produces a larger min/mile number than min/km. The cards always show pace in the unit you've selected.
Marathon distance — 42.2 or 42.195?
The marathon preset uses 42.195 km exactly (26.2 miles is a rounding). Same for the half at 21.0975 km.
Does this account for walk-run intervals?
No. Pace, time, and distance are linked by a single average speed. For interval planning, compute each segment separately.
How accurate is the time-from-pace projection?
Linear projection assumes you hold the pace. Real races slow down in the second half — a marathon based on your 10K pace will usually finish 5-10% slower.
Switching units changed my distance slightly — why?
The unit toggle converts the number in the distance box and rounds it to two decimals, because that is the precision the field shows. A marathon set as 42.195 km becomes 26.22 mi, and switching back gives 42.2 km — five metres off. It is invisible at race distances but it compounds if you flip units repeatedly, so re-pick the preset instead of toggling back and forth.
How much is ten seconds per kilometre actually worth?
Over a marathon, 10 s/km is 7:02 of finishing time; over 10K it is 1:40. In speed terms the same 10 s buys more the faster you already are: 6:00/km to 5:50/km is 10.00 to 10.29 km/h, while 4:00/km to 3:50/km is 15.00 to 15.65 km/h. Pace and speed are reciprocals, so equal pace steps are not equal speed steps.
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