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Running Pace Calculator

Enter a distance and your time to get pace per km, pace per mile and average speed, plus predicted finish times for common race distances.

The first thing runners ask each other is the pace, and pace is the common language of the sport as well as the basis for setting a race goal and planning training intensity. Put in the distance and the time from one run and, along with the minutes per kilometre, it works out how long 5 km, 10 km, a half and a full marathon would take at that rhythm — enough to know where you stand before entering.

On conventions: pace is time divided by distance, and GPS watches generally read 1–2% long because of corner cutting and tree cover, so an official chip time is the one that counts; the predicted finish times assume an even pace throughout, while slowing in the second half is normal, so leave five to ten minutes of margin when setting a target.

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How to use

  1. Enter the distance and your time.
  2. Read the pace per kilometre and per mile, and the average speed.
  3. Check the predicted times for the standard race distances.
  4. Leave five to ten minutes of margin when setting a goal.

How it works

How pace is computed

Pace is simply time divided by distance. For example 10 km in 45 min 30 s (2,730 seconds): 2,730 / 10 = 273 seconds, i.e. 4 min 33 s per km, written 4:33/km. Conversely, from pace and target distance you can derive time: 4:33 for 5 km is about 22 min 45 s.

Why half marathon extrapolates but full doesn't

The finish projection in the table assumes even pacing. Over 10 km and half-marathon distances the assumption is fairly close to reality; over a full marathon it breaks down — hitting the wall, fueling and temperature all slow the second half, and most people run 3-8% slower than the best-pace projection. So the marathon row is an "optimistic lower bound," not a target time.

Time format

Time can be written as 45:30 (min:sec) or 1:45:00 (hour:min:sec), or entered directly in seconds like 2,730. Distance supports decimals; 21.0975 for a half and 42.195 for a full are most accurate — don't approximate with 21 or 42, or the pace shifts by more than ten seconds.

Code example

JavaScript Pace and race finish times 

function pace(km, seconds) {
  const perKm = seconds / km;
  const fmt = (s) => {
    const m = Math.floor(s / 60), sec = Math.round(s % 60);
    return m + "\u2032" + String(sec).padStart(2, "0") + "\u2033";
  };
  return {
    perKm: fmt(perKm),
    speedKmh: (km / seconds * 3600).toFixed(1),
    races: { "5K": fmt(perKm * 5), "10K": fmt(perKm * 10),
             half: fmt(perKm * 21.0975), full: fmt(perKm * 42.195) }
  };
}

Python The same formulas in Python 

def pace(km, seconds):
    per_km = seconds / km
    fmt = lambda s: f"{int(s // 60)}\u2032{s % 60:04.1f}\u2033"
    return {"per_km": fmt(per_km),
            "speed": round(km / seconds * 3600, 1),
            "full": fmt(per_km * 42.195)}

pace(10, 3300)   # 5\u203230.0\u2033/km, full marathon ≈ 3:51:52

FAQ

How does pace differ from speed?

Pace is "how long to run one kilometer" (like 4:33/km) and speed is "how many kilometers per hour" (like 13.19 km/h) — reciprocals. Runners habitually read pace (lower is faster), while cycling and treadmills usually show speed.

What level is a 1:45 half marathon?

About 4:59 per km, upper-middle among amateur runners, usually requiring a weekly mileage base and ease at 15 km+ long runs. At the same pace, 10 km is about 49:46 and a marathon theoretically 3:30, though the actual result depends on endurance reserves.

Why can't the marathon just be pace times distance?

Because its distance is long: glycogen depletion, dehydration and muscle fatigue slow the second half, so most run 3-8% slower than the even-pace projection, and first-timers often 10% or more. Use rules of thumb like "half time x 2 + 10 minutes" for a marathon goal, with margin.

What time formats are supported?

45:30 (min:sec), 1:45:00 (hour:min:sec) and plain seconds 2,730. Chinese-style "45 min 30 s" isn't supported, nor more than three segments (like 1:2:3:4). A wrong format gets a direct prompt, not a silent wrong value.

How do pace and heart-rate zones work together?

Pace is objective output; heart rate is bodily load. The same pace raises heart rate on hot days, hills or when fatigued. In training, set intensity by heart-rate zone and record performance by pace — the two together track progress reliably.

How do I convert treadmill speed to pace?

Take the reciprocal and convert: 12 km/h gives 60 / 12 = 5 minutes/km, i.e. 5:00/km. A treadmill has no wind resistance, so the speed reads slightly higher at the same perceived effort — use a 1% incline to simulate outdoors.

Why is my actual run very different from the projection?

The projection assumes even pacing and ignores heart rate. Starting too fast, heat, rolling terrain and poor fueling all slow you down; conversely, greatly increased recent training may make you faster. Treat it as a same-pace conversion reference, not a performance prediction.