How to use it
- Choose what you want to find. Pace, time or distance. The box for that one disappears and the other two stay.
- Fill in the other two. Tap a common distance or type your own. Times can be written as h:mm:ss, mm:ss or plain minutes, so "25", "25:00" and "0:25:00" all mean the same run.
- Read the answer and the tables. The splits show where you should be at every kilometre or mile, or every lap of a track for shorter runs. The predictor turns your run into estimated times for the classic race distances.
Switching between km and mi converts your pace with you, and the link in the address bar keeps your numbers, so you can bookmark a target or send it to a training partner.
Pace or speed
Runners talk in pace: minutes and seconds per kilometre or mile. Treadmills and bikes talk in speed: kilometres or miles per hour. They are the same number turned upside down. To go from pace to speed, divide 60 by the pace in minutes, so 5:00 per km is 12 km/h and 6:00 per km is 10 km/h.
Pace is easier to run by, because it maps straight onto your watch and onto the splits. Speed is easier to set on a machine. The calculator shows both so you never need to do the sum on the belt.
Even and negative splits
An even split means every kilometre takes the same time. A negative split means the second half is a little faster than the first. Both beat the most common race plan, which is going out too fast and hanging on.
Going out 10 seconds per kilometre too quick feels easy for the first few minutes, then costs far more than 10 seconds a kilometre at the end. Use the splits table as a set of checkpoints. If you are ahead of it early, ease off. If you are on it at halfway and still feel good, that is the time to press.
A simple rule for a first race: run the first third slightly slower than target, the middle third on target, and whatever you have left in the last third.
Pacing the runs in a hybrid race
A hybrid race puts a 1 km run before each of eight workout stations, so you cover 8 km in total with sleds, wall balls and lunges in between. Those runs are slower than a fresh 8 km, because your legs are already cooked when each one starts.
- Pick a pace you can hold on run eight, not run one. The first kilometre always feels easy, and it is where most people lose their race.
- Treat the first 200 m of each run as a reset. Let your breathing settle after the station, then build into target pace.
- Practise it. Tap the 8 x 1 km chip, set your target time, and use the per 400 m figure to pace repeats on a track between stations in training.
For the station work itself, set up intervals on the WOD timer and run your 1 km repeats off the numbers here.
Easy pace is slower than you think
Most of a runner's week should be easy running, and for most people easy is much slower than race pace. A useful guide is that you can talk in full sentences. In numbers, easy runs often sit somewhere around 60 to 90 seconds per kilometre slower than your 5k race pace.
Put a recent 5k into the calculator, add a minute or so to the pace, and that is a sensible starting point for easy days. The hard sessions only work if the easy ones are genuinely easy.
How the race predictor works
The predictor uses the Riegel formula, published by Peter Riegel in the 1970s and still the most widely used way to guess one race time from another:
Predicted time = your time × (new distance ÷ your distance) to the power of 1.06.
The 1.06 is what makes you a little slower per kilometre as races get longer. A 20:00 5k predicts a 10k of about 41:42.
It is honest over small jumps, like 5k to 10k. Over big ones, like 5k to marathon, it assumes you have done the endurance training for the longer race, which most people have not. Treat a marathon time predicted from a short race as the best case, not a plan.