Pace calculator: running pace, splits and equivalent race times

Pace per kilometre for 25:00 over 5 kmworked example

5:00 / km

Per kilometre: 5:00 /km
Per mile: 8:03 /mi
Per 400 m lap: 2:00
Speed: 12 km/h
Speed: 7.46 mph
Distance in kilometres: 5 km

Pace is time divided by distance, so this part is exact arithmetic and every rounding you see happens at the last moment, on screen. The equivalent-time table below is a different kind of number: it comes from Riegel's 1981 fit to world records, and it assumes you are as well trained for the new distance as for the one you actually ran.

Finish time25:00, 1:45:30 or plain seconds all parse.DistanceOr pick a standard race below.

Distance unit

Both split tables are always computed.

Standard races

Even splits, per kilometre
Marker	Segment	Cumulative
1 km	5:00	5:00
2 km	5:00	10:00
3 km	5:00	15:00
4 km	5:00	20:00
5 km	5:00	25:00

The fractional final segment is spelled out rather than dropped. A marathon is 42 kilometres plus 195 metres, and that last stretch is where a plan built on round numbers stops matching the clock.

Equivalent times at the standard distances (Riegel 1981)
Race	Predicted time	Pace /km	Pace /mi
5K (your run)	25:00	5:00	8:03
10K	52:07	5:13	8:23
Half marathon	1:55:00	5:27	8:46
Marathon	3:59:47	5:41	9:09

T2 = T1 x (D2/D1)^1.06, fitted by Riegel to world records from 100 metres to 100 miles. A doubling of distance costs about 8.5 percent more than double the time, which is why a 25-minute 5K projects to 52:07 rather than 50:00 over 10K.

Realistic range

3:59:47 to 4:21:08

The 1.06 exponent was fitted to world-record performances from 100 m to 100 miles, and Riegel found it close to constant across events and across groups of runners. It assumes you are equally trained for both distances, and it is most optimistic exactly where it is most used: predicting a marathon from a short race, where the limit is fuelling and durability rather than speed. The tool therefore shows the prediction at 1.06 alongside 1.08 and 1.10 so it reads as a spread.

The same marathon prediction at three fatigue exponents
Exponent	Predicted marathon	Whose number this is
1.06	3:59:47	Riegel's, fitted to world records
1.08	4:10:14	ours, as a sensitivity check
1.1	4:21:08	ours, as a sensitivity check

Only 1.06 is Riegel's. The steeper exponents are this site showing you what the same input predicts if you fade harder than a record-holder, because a marathon projected from a short race is limited by fuelling and durability rather than by speed.

Every common target at every standard distance has its own page. For example sub-2:00 half marathon, sub-4:00 marathon or sub-25:00 5K.

A running pace calculator converts a finish time and a distance into pace per kilometre and per mile, with even splits for every marker including the fractional last one. It also projects equivalent times at 5K, 10K, half marathon and marathon using the Riegel equation, shown as a spread rather than a promise.

Equivalent race time (Riegel) — T2 = T1 x (D2 / D1)^1.06. Verified 2026-07-30 against Riegel, American Scientist 1981 (The 1.06 exponent was fitted to world-record performances from 100 m to 100 miles, and Riegel found it close to constant across events and across groups of runners. It assumes you are equally trained for both distances, and it is most optimistic exactly where it is most used: predicting a marathon from a short race, where the limit is fuelling and durability rather than speed. The tool therefore shows the prediction at 1.06 alongside 1.08 and 1.10 so it reads as a spread.)
Mile to kilometre conversion — 1 mile = 1.609344 km (exact, by definition). Verified 2026-07-30 against NIST Special Publication 811, Guide for the Use of the International System of Units (None - the international mile is defined as exactly 1609.344 metres, so this conversion is exact and every rounding you see is ours, at the display edge only.)

Everything you type here is computed in your browser. Nothing you enter is stored on a server, sent anywhere, or shared — there is no account and no health data to leak.

Frequently asked questions

How do you calculate running pace?

Divide your total time by the distance. A 5 kilometre run in 25 minutes is 1500 seconds over 5 kilometres, which is 300 seconds or 5 minutes per kilometre, and 8 minutes 3 seconds per mile. This tool also gives your 400 metre lap pace and your speed in km/h and mph.

How do you predict a race time from another distance?

The Riegel equation: your new time equals your old time multiplied by the ratio of the distances raised to the power 1.06. Riegel fitted that exponent to world records from 100 metres to 100 miles. A doubling of distance therefore costs about 8.5 percent more than double the time.

Is the Riegel prediction reliable for a marathon?

It is most optimistic exactly where it is most used. Predicting a marathon from a 5 kilometre time assumes you are equally trained for both, and the marathon is limited by fuelling and durability rather than speed. This tool prints the prediction at 1.06 alongside 1.08 and 1.10 so it reads as a range.

What pace do I need for a sub 2 hour half marathon?

2 hours over 21.0975 kilometres is 5 minutes 41 seconds per kilometre, or 9 minutes 9 seconds per mile. Enter the target and the tool gives the splits, and there are dedicated pages for the common targets at every distance.

Why does the last marathon split look odd?

Because a marathon is 42 kilometres plus 195 metres, and most split tables quietly drop the 195. This one spells the fractional final segment out, since that stretch is where a plan built on round kilometres stops matching the clock.

Should I run even splits?

This tool computes even splits because that is the arithmetic; whether to race that way is a coaching question it does not answer. What it can show you is exactly what your target pace demands at each marker, in whichever unit you actually think in.

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The next number

No body metric means much on its own. Here is what this one feeds into.

Heart rate zone calculatorPace is the outside of the effort; heart rate is the inside. Most training plans want both.Calories burned calculatorWhat that run cost, from the Compendium MET row for running at your actual pace.

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Every formula on this page is listed with its source on the methodology page, and changes to any reference value are logged in the data changelog. Canonical URL: https://myhealthmywellness.com/pace-calculator