Running Pace Calculator

How to Use the Running Pace Calculator

Pace, time and distance are three views of one relationship, and knowing any two gives you the third. This calculator solves in all three directions, prints a splits table you can read off a watch, and projects equivalent times at other race distances.

1. Pick what you are solving for. Solve for pace when you have run something and want to know how fast. Solve for time when you have a target pace and want a finishing time. Solve for distance when you know how long you ran and at what pace.
2. Choose kilometres or miles. Everything on the page follows this setting, and the pace in the other unit is shown alongside so you never have to convert by hand.
3. Fill in the two quantities you know. The fields you do not need disappear, so there is never an ambiguous input on screen.
4. Read the splits table. It gives cumulative elapsed time at each whole kilometre or mile, which is the format you actually check against a watch mid-race.

The equivalent race times underneath use Riegel's formula, which projects performance across distances for a runner trained comparably at each. It is a prediction from one data point, not a promise.

Pace, Time and Distance Formulas

The core relationship is one division, and everything else on the page is a rearrangement of it or a unit conversion.

Riegel's exponent is the interesting part. If endurance were perfect the exponent would be 1.0 and doubling the distance would exactly double the time. It is 1.06 instead, which means doubling the distance costs about 4.2% more than double the time — that is 2^1.06 = 2.0851 rather than 2. That small excess is fatigue, measured across thousands of race results.

Because the exponent compounds, the formula is reliable across a two- or threefold range of distances and increasingly optimistic beyond it. Projecting a marathon from a 5K stretches it more than eight times and will usually flatter the runner, since it assumes marathon-appropriate training that a 5K result cannot demonstrate.

Example

Worked example one: 10 km in 52 minutes 30 seconds. The total is 52 × 60 + 30 = 3,150 seconds. Pace is 3,150 ÷ 10 = 315 seconds per kilometre, which is 5:15 per km. Speed is 10 ÷ (3,150 ÷ 3,600) = 11.43 km/h, or 11.428571 ÷ 1.609344 = 7.10 mph.

In the other unit, 315 × 1.609344 = 506.94 seconds per mile, which is 8:26.9 per mile. The splits table then simply multiplies: 5 km arrives at 5 × 315 = 1,575 seconds, or 26:15.0, exactly half the finishing time because the pace is even.

Worked example two: what that predicts elsewhere. Riegel takes the 3,150-second 10K and scales it. For the 5K, 3,150 × (5 ÷ 10)^1.06 = 3,150 × 0.479632 = 1,510.8 seconds, or 25:10.8 — not 26:15, because half the distance costs less than half the time.

For the half marathon, 3,150 × (21.0975 ÷ 10)^1.06 = 3,150 × 2.206403 = 6,950.2 seconds, which is 1:55:50. For the marathon, 3,150 × (42.195 ÷ 10)^1.06 = 3,150 × 4.600200 = 14,490.6 seconds, or 4:01:31. Notice the pace decay: 5:02 per km for the 5K, 5:15 for the 10K, 5:29 for the half and 5:43 for the marathon.

Reading Your Splits and Projections

The first thing worth checking is whether your splits were actually even. The table on this page assumes they were, because that is what a single average pace means. If you ran the first half of that 10K in 25:00 and the second in 27:30, the average is still 5:15 per km and it describes a race you did not run.

Even pacing is close to optimal for anything from 1,500 m upwards, and almost every world record at those distances has been set with a slightly negative split — the second half marginally faster than the first. Starting too fast is the most common and most expensive mistake in distance racing, and it costs more than the time it appeared to gain.

Read the projections as a range rather than a target. If your marathon prediction from a 10K says 4:01:31, plan for something between four hours and four and a half, because the formula assumes marathon-specific endurance that a 10K cannot prove you have. Runners who train high mileage tend to beat their projections; runners who race well over short distances and train little tend to miss them badly.

The speed figure is mainly useful for treadmills, which are set in km/h or mph rather than in pace. 5:15 per km is 11.43 km/h, and knowing that saves converting on a machine while already running.

Finally, pace is not effort. The same 5:15 per km costs far more on a hilly course in warm weather than on a flat track in cool conditions, which is why comparing raw paces between races tells you less than it appears to.

Five Things That Move Your Pace

Five things that move the number more than most runners expect.

Heat. Marathon times degrade measurably above about 15°C, and the effect grows with distance because heat accumulates. A time set at 25°C is not comparable with the same effort at 10°C, and pacing to a personal-best schedule on a hot day is how races go wrong at thirty kilometres.

Hills. The common rule of thumb is that climbing costs more than descending returns, so a rolling course is slower than a flat one of the same total elevation change. Pacing by effort rather than by the watch is the standard advice on undulating courses.

GPS error. A watch measuring 10.15 km on a certified 10 km course is normal, caused by tracking error and by not running the shortest legal line. That 0.15 km makes your displayed average pace about five seconds per kilometre faster than your official one, which is why watch pace and race pace rarely agree.

Surface. Trail, sand and deep grass cost time at identical effort, sometimes a great deal of it. Treadmill running is usually slightly easier at the same displayed speed because there is no air resistance, which is what the 1% incline convention is meant to offset.

Training specificity. Riegel assumes comparable training at each distance, and that assumption does the heavy lifting. Somebody who races 5K well on forty kilometres a week will not hit their projected marathon, because the projection is describing a runner with marathon endurance rather than the runner who produced the input.

If you are pacing a training block around bodyweight or fuelling as well, the calorie calculator covers intake and the TDEE calculator covers how much running actually adds to daily expenditure.