Running Pace Calculator

How to use this calculator#

1. 1
   Choose which of the three values you wantPace, time and distance are locked together, so fix any two and the third follows. Solve for pace after a run, for time when you want to know what a target pace produces, and for distance when you know how long you have and how fast you intend to go.
2. 2
   Enter time as hours, minutes and seconds, not decimals52 minutes 30 seconds is 52:30, not 52.5 unless the field asks for decimal minutes. Treating 8:30 as 8.30 is the classic error and understates pace by 18 seconds a mile — enough to wreck a race plan over a marathon.
3. 3
   Keep distance and pace in the same unitA pace in minutes per mile against a distance in kilometres gives an answer that is wrong by 61%. Set the unit toggle first, and remember that a mile is 1.609344 km.
4. 4
   Read the equivalent race times as arithmetic, not prophecyThey show what each standard distance takes at exactly the pace you entered. They are a straight multiplication with no physiology in them, which is why a 5K pace extrapolated to a marathon produces a time almost nobody can run.
5. 5
   Use Riegel's model to predict across distancesRaising the distance ratio to the power of about 1.06 accounts for the fact that sustainable pace falls as distance grows. It assumes appropriate training for the longer distance — a 5K runner who has never run beyond 15 km will not hit its marathon prediction.

The formula#

The three-way pace relationship#

Pace, time and distance are locked together: pace equals time divided by distance, time equals pace multiplied by distance, and distance equals time divided by pace. Fix any two and the third follows. Running 10 km in 52 minutes gives 5:12 per kilometre, or 8:22 per mile, since a mile is 1.609 kilometres.

Speed is the inverse of pace and is sometimes easier to compare: 5:12 per kilometre is 11.54 km/h. Treadmills and cycling computers usually show speed, while road runners think in pace, so being able to flip between them is genuinely useful.

Reading the equivalent race times#

The equivalent finish times show what each standard distance would take at exactly the pace you entered: 5 km, 10 km, 21.0975 km for the half marathon and 42.195 km for the full. They are a straight multiplication, not a physiological prediction.

In reality nobody holds 5K pace for a marathon. Riegel's model, which raises the distance ratio to the power of about 1.06, suggests a runner finishing 5K in 25 minutes is closer to 4:00 for a marathon than the 3:31 that flat extrapolation implies. Use the equivalents to plan pacing at one distance, not to set a marathon goal from a parkrun.

Pacing a race and staying safe#

Even or slightly negative splits produce the best results for most runners. Going out 10 seconds per kilometre faster than goal pace in the first 5 km of a marathon typically costs far more than that over the last 10 km, as glycogen depletion and rising core temperature take hold. Heat, humidity, wind and elevation all slow realistic pace targets.

This is a maths tool, not coaching or medical advice. Build weekly mileage gradually, roughly 10% at a time, to reduce injury risk. Get checked by a doctor before starting a running programme if you are new to exercise or have a heart condition, and stop for chest pain, dizziness or sharp joint pain.

Worked examples#

Reference tables#

Common mistakes#

• Entering time as a decimal8:30 per mile is 8 minutes 30 seconds, which is 8.5 in decimal minutes, not 8.30. The 0.2-minute error is 12 seconds a mile — about five minutes across a marathon, which is the difference between a personal best and missing one.
• Extrapolating a short-distance pace to a long raceFlat multiplication assumes sustainable pace is independent of distance, which it is not. A 25-minute 5K runner extrapolates to a 3:31 marathon and, by Riegel, should expect closer to 4:00. Going out on the flat-extrapolated pace is the standard route to a collapse after 30 km.
• Mixing kilometres and milesA pace entered in minutes per mile against a distance in kilometres produces an answer 61% out. Race distances are also easy to fumble: the marathon is 42.195 km and the half is 21.0975 km, not 42 and 21.
• Ignoring conditions and terrainHeat, humidity, wind and elevation gain all slow realistic pace, and heat is the largest of them — hot, humid conditions can cost several minutes over a marathon and materially raise the risk of heat illness. A pace calculated in cool conditions is not a plan for a hot race day.

Frequently asked questions#

Key terms#

Pace

Time taken per unit distance, written as minutes and seconds per kilometre or per mile. The inverse of speed.

Split

The time recorded for a segment of a race, such as each kilometre or each 5K. Even or slightly negative splits produce the best results for most runners.

Negative split

Running the second half of a race faster than the first. Widely associated with better finish times than starting fast and fading.

Riegel formula

T₂ = T₁ × (D₂ ÷ D₁)^1.06, a model for predicting performance at one distance from a result at another. The exponent above 1 encodes the fact that pace falls as distance rises.

Threshold pace

Roughly the fastest pace sustainable for about an hour, near the lactate threshold. Often close to 10K–15K race pace for trained runners.

Marathon distance

42.195 kilometres, or 26 miles 385 yards — 26.219 miles. Fixed by World Athletics rules; the half marathon is exactly half, 21.0975 km.

Sources#