How do you calculate running pace?

Divide your time by the distance. Ten kilometres in fifty minutes is 50 ÷ 10 = 5 minutes per kilometre, written 5:00 /km. To go the other way, multiply pace by distance: a 5:00 /km pace over 42.195 km gives 3 hours 30 minutes 59 seconds. Pace is the reciprocal of speed, so 5:00 /km is exactly 12 km/h — the two carry identical information in different units.

How do I convert pace between kilometres and miles?

Multiply a per-kilometre pace by 1.609344 to get per-mile, and divide to go back. A 5:00 /km pace is 8:03 per mile; a 7:00 /km pace is 11:16. Because the mile is defined as exactly 1609.344 metres the conversion is exact rather than approximate, so converting back and forth never drifts.

What pace do I need for a sub-3 hour marathon?

4:16 per kilometre, or 6:52 per mile, held for the whole 42.195 km. Sub-4 needs 5:41 /km, and sub-5 needs 7:07 /km. Those are averages including any slowing in the closing miles, so most runners aim to start a few seconds per kilometre slower than target and rely on even or slightly negative splits rather than banking time early.

How accurate is a race time prediction?

Riegel's formula is a good guide between nearby distances and progressively less reliable as the gap widens. Predicting a 10K from a 5K is usually within a percent or two; predicting a marathon from a 5K is optimistic for most runners, because it assumes you have the endurance base to sustain the effort. The formula describes what is physiologically plausible given similar training, not what your body will do on a particular day.

Why does the exponent 1.06 matter?

Because it is greater than one, which is what makes the model say anything useful. If the exponent were exactly 1, doubling the distance would double the time and you could hold your 5K pace forever. The value 1.06 encodes the observed fact that pace degrades as distance grows — roughly four percent slower per doubling. Setting it higher makes the model more conservative, which suits runners with less endurance base.

How long is a marathon exactly?

42.195 kilometres, or 26.219 miles — a defined figure rather than a rounded one. The odd distance comes from the 1908 London Olympics, where the course was set from Windsor Castle to the royal box in the stadium, and it was formally standardised in 1921. A half marathon is exactly half of it, 21.0975 km. Using 42.2 instead introduces a five metre error, which is about a second of finish time at most paces.

Should I run even splits or negative splits?

Even or slightly negative for almost everyone. A negative split means running the second half marginally faster than the first, and it is how most personal bests and world records are actually run. Starting fast feels easy and costs far more later than it gains early — the time banked in the first few kilometres is typically repaid several times over in the closing ones. The split table on this page assumes an even pace throughout.

What is a good running pace?

It depends entirely on distance, experience and what you are training for, and comparing yourself to a single number is rarely useful. As rough context, many recreational runners sit between 6:00 and 7:00 per kilometre for a comfortable run, well-trained club runners around 4:00 to 5:00, and elite marathoners under 3:00. Far more informative than any of those is your own trend — the same route getting easier at the same pace is progress, whatever the number says.

Does my GPS watch measure distance accurately?

Usually within one or two percent, which is enough to shift a pace reading by several seconds per kilometre. GPS tends to overestimate on winding routes and under tree cover, and race courses are measured along the shortest legal line, so almost everyone records slightly more than the official distance. This is why a watch commonly shows 42.4 km at the end of a marathon, and why races are timed by chip rather than by anyone's watch.

Running Pace Calculator

Work out your pace from a distance and a time, your finish time from a distance and a pace, or how far you went from a time and a pace. Fill in any two of the three and the calculator returns the third, along with your speed in both km/h and mph, a split for every kilometre, and what the same effort...

TIME = DISTANCE × PACE

Solving for pace.

DISTANCE

FINISH TIME — h:mm:ss or mm:ss

PACE — mm:ss

solved: 5:00 / km

RACE DISTANCES

PACE

5:00 / km

PER MILE

8:03

SPEED

12.00 km/h

IN MPH

7.46 mph

10.00 km in 50:00 — pace and speed are reciprocals, so 5:00 per km is the same thing as 12.00 km/h.

SPLITS — EVERY 1 KM

1 km