Pace Calculator (Running)

A pace calculator converts between pace, in minutes per mile or per kilometre, speed and finish time for a given distance. Know two of the three and it works out the third. The common UK race distances are parkrun at 5 km, 10 km, the half marathon at 21.1 km and the marathon at 42.2 km. Converting between the two units means multiplying minutes per kilometre by 1.609, so 5:00/km is 8:03/mile, and the 4:15/km needed for a sub-3 marathon is 6:50/mile.

Enter a distance and either your target time or your pace and you get pace per km and per mile, average speed in km/h and mph, a split table and predicted finish times for the standard distances. The splits are the part most runners use on race day, because even pacing beats going out fast and hanging on. A half marathon in 1 hour 50 minutes works out at 5:13/km, or 8:23/mile, at 11.5 km/h.

Real finishing times give those numbers some shape. The average parkrun 5km takes 28:30, which is 5:42/km or 9:11/mile. The average London Marathon finish is 4:30, at 6:24/km or 10:18/mile. At the sharp end, the men's marathon world record of 2:01 set by Kelvin Kiptum runs at 2:52/km, or 4:37/mile, and the UK parkrun record of 13:31 belongs to Marc Scott.

Predicting one distance from another uses the Riegel formula, where T₂ equals T₁ multiplied by (D₂/D₁) raised to the power 1.06. Run 10K in 50 minutes and it predicts 110 minutes, or 1:50, for a half marathon and 230 minutes, or 3:50, for a marathon. The caveat is that it assumes you have trained equally for both distances, and most amateurs come in 5 to 15% slower over a marathon because they have not. Yasso 800s offer a rougher check, since running 10 repetitions of 800m gives an average time in minutes and seconds that predicts the marathon in hours and minutes, so 3:30 repeats suggest a 3:30 marathon.

Heart rate zones tie pace to effort. Zone 1 at 50 to 60% of maximum heart rate is recovery pace, easy enough to hold a conversation. Zone 2 at 60 to 70% is the aerobic base you can sustain for hours while still talking in sentences. Zone 3 at 70 to 80% is tempo, where speech drops to short phrases, and Zone 4 at 80 to 90% is threshold, single words only and sustainable for about an hour. Zone 5 at 90 to 100% is anaerobic and lasts minutes. Marathon pace sits at the top of Zone 2 or the bottom of Zone 3, 10K pace in mid Zone 4, and 5K pace at the top of Zone 4.

The standard distances are worth knowing exactly. A half marathon is 21.0975 km, or 13.1 miles, and a marathon 42.195 km, or 26.2 miles, with anything longer counted as an ultramarathon. Parkrun is free and starts at 9am every Saturday. Trail and fell running in Britain are usually measured in metric, though terrain matters more than pace on them. Getting into the London Marathon means a ballot with roughly a 1-in-15 chance, a Good For Age qualifying time such as sub-3:15 for M40, or a charity place carrying a fundraising commitment of £2,000 and up. The Bob Graham Round, 66 miles over 42 peaks and 27,000 feet of ascent inside 24 hours, is the domestic ultra test piece.

Building pace is mostly about restraint. The 80/20 rule puts 80% of training at easy pace in Zones 1 and 2 and 20% hard in Zones 4 and 5, and the common amateur error is filling the week with medium effort that delivers neither base nor intensity. Long runs should grow by 5 to 10% a week and never jump more than 25% in one week, with a recovery week every 3 to 4 weeks cutting volume by 25 to 30%. Easy pace should sit 60 to 90 seconds per km slower than goal race pace. Tempo runs go at threshold, and speed work uses 400m, 800m and 1km repeats faster than race pace.