Treadmill pace chart

Treadmills in the US display miles per hour; almost everywhere else they display kilometres per hour. The first two columns are the same speed in both, so the chart works whichever console you are standing on.

The conversion itself has no science in it. A mile is 1.609344 kilometres, so 6.0 mph is 9.66 km/h, which is a 10:00 mile and a 6:13 kilometre. The finish columns are just that speed held for the whole distance — 6.0 mph for 5K takes 31:04, and for a marathon, 4:22:11.

Why your treadmill pace feels harder than the road

Two things are different indoors. There is no air to push through, which makes the belt slightly easier than the road at the same speed, and the belt is moving under you, which changes almost nothing about the work but changes a great deal about how it feels. The first effect is real and small; the second is why an easy run indoors can feel like a tempo.

The advice to set the treadmill to 1% comes from a single 1996 study by Jones and Doust, which found that a 1% grade made the oxygen cost of treadmill running match outdoor running at speeds between about 2.9 and 5.0 metres per second — roughly 5:35 to 3:20 per kilometre. That is a real result with a narrow scope. If you run slower than about 5:35/km, the air resistance you are compensating for is not there to compensate for, and 1% is simply a hill.

The incline table above uses the ACSM running equation, the standard model for the oxygen cost of graded running. It prices 1% of grade at roughly 4.5% of speed. So 6.0 mph at 1% costs about what 6.27 mph costs on the flat, which is a 9:34 mile rather than a 10:00 one. At 5% the same belt speed is worth an 8:10 mile.

Both of those are statements about oxygen, not about race results. Running uphill and running fast are not interchangeable training stimuli, and no equation makes them so.

The treadmill is not a compromise. It is the most controllable surface you will ever train on, and there are workouts it does better than any road:

• Pace discipline. The belt does not let you drift. For a runner who starts every tempo 15 seconds too fast, that is worth more than fresh air.
• Hill repeats without a hill. 4–6% for 60–90 seconds gives you the strength stimulus of a hill session in a flat city.
• Progressions. Nudging the speed up 0.1 mph every kilometre is trivial indoors and nearly impossible to judge outdoors.

What it does badly is teach you to pace yourself, run tangents, or handle wind. Keep at least one outdoor run a week when you are training for an outdoor race.