Guides · The 1% incline rule
The 1% treadmill incline rule, and the thing it assumes
You step on, set your pace, and tap the incline up to 1.0 before your first stride, because that is what makes the belt feel like outside. You have never checked what that 1 is correcting, or what it takes for granted.
Yes, for steady running between about 5:22 and 9:11 a mile, 1% is a sound way to match the effort of the road. The rule comes from one 1996 study of nine trained male runners. It makes up for the air you would push at your real speed, so it assumes the belt runs the speed on the display.
Where the 1% incline rule came from
The 1% incline rule traces back to one lab study published in 1996. Nine trained male runners who were used to treadmills ran six speeds from about 9:11 down to about 5:22 a mile, for 6 minutes each. They ran every speed on a treadmill at flat, 1%, 2% and 3%, and once on a level road, while the researchers measured their oxygen use.
The reason for a hill is air. Outdoors, moving through the air takes work. On a treadmill you stay in one spot, so that work goes away, and a slight grade adds some back. The belt can still feel harder than the road for other reasons, and those live in the treadmill pace vs road pace guide.
Does 1% incline make a difference? It depends on your pace
Which grades matched the road at each speed
The 1996 result for nine trained male runners. A grade counts as a match when the study found its effort not significantly different from the road.
| Speed | Pace, about | Grades that matched the road |
|---|---|---|
| 6.53 mph | 9:11 | Flat or 1% |
| 7.45 mph | 8:03 | Flat or 1% |
| 8.39 mph | 7:09 | 1% only |
| 9.33 mph | 6:26 | 1% or 2% |
| 10.25 mph | 5:51 | 1% or 2% |
| 11.18 mph | 5:22 | All four grades; road effort fell between 1% and 2% |
Paces are per mile. The mph and pace figures are my conversions of the study’s meters per second.
So 1% is the one grade that matched the road at every speed tested. A flat belt did as well at the slow end, and nothing slower than about 9:11 a mile was tested. The rule is not a myth. It is narrower than people repeat. One 2024 study found that on the one treadmill model it tested, running at 1% still took more effort than the track.
What the 1% incline assumes
The 1% incline assumes the belt moves at the speed your display shows. The correction is sized for the air you would push at the pace you are really running. Your display shows the speed the belt was asked for, and you cannot confirm from the display that the belt is doing it.
Think of a golfer who takes one extra club into the wind. Clubbing up is a smart correction. It still trusts the yardage on the marker. If the marker is 20 yards wrong, the extra club carries the right correction to the wrong distance. Your 1% is the extra club, and the belt’s speed is the yardage.
The incline number comes from the machine as well. The deck reaches its grade from the machine’s own reference point, and the display gives you no way to check that reference against the floor. The guide on how your treadmill sets its incline, and how to check it with your phone covers that half.
What a small belt error does to your 1% run
Say you set 7.9 mph, a 7:36 mile inside the tested band, and add 1%.
A 7.9 mph setting at 1% on three belts
All three were set to a 7:36 mile. I invented these belts rather than measuring them.
| Belt | True mph | True pace |
|---|---|---|
| Exactly right | 7.90 | 7:36 |
| 2 percent slow | 7.74 | 7:45 |
| 2 percent fast | 8.06 | 7:27 |
Paces are per mile. A 2021 lab study found average belt speed between 98 and 103 percent of the setting on four treadmills, one of them badly worn, so 2 percent either way is within that range.
On the slow belt, your 1% evened out the effort of a 7:45 run, not the 7:36 in your log. If you build a road race pace from that session, you start 9 seconds a mile too fast. On the fast belt, your log undersells the run you really did.
Keep the 1%, check the speed
Keeping the 1% makes sense for steady running in the tested band, and flat did as well at the slow end of that band. Before you trust the pace it corrects, find out what the belt really does at that setting. If the belt is off, the adjustment belongs to your owner’s manual or a service technician. Your watch cannot settle this indoors either. The guide on why your watch estimates treadmill pace from your wrist instead of the belt shows what it is really counting.
Check the belt under your 1%
Treadwell measures the belt itself, using the LiDAR sensor and camera on an iPhone Pro. Flatten the deck, run the belt empty at the pace you usually pair with 1%, and let the phone read it while you stay on the floor. Then you know which pace your extra club is really correcting.
Know the pace under your 1%
Find out what your belt really runs before you trust the correction on top of it. The reading comes from the LiDAR sensor, so Treadwell runs only on an iPhone Pro.
Scan with your iPhone Pro to get the appTested: in our tachometer tests the app read within about 2 percent of true belt speed.
Quick answers
Is 1% incline on a treadmill good? Yes, for steady running between about 5:22 and 9:11 a mile, 1% is a sound way to match the effort of the road. The rule comes from one 1996 study of nine trained male runners. It makes up for the air you would push at your real speed, so it assumes the belt runs the speed on the display.
Does 1% incline make a difference at slow paces? At the two slowest speeds the 1996 study tested, about 9:11 and 8:03 a mile, a flat belt matched the road as well as 1% did for its nine trained male runners. Nothing slower than about 9:11 a mile was tested, so the study cannot say whether 1% matters there.
Does 1% incline fix a treadmill that runs slow? No. A 1% incline only makes up for the air you would push outdoors at the speed you are really running. It cannot tell whether the belt matches the display, so a slow belt is just as slow at 1%.
Sources.
- Where the 1% rule comes from, and the speed by speed table: Jones AM and Doust JH, “A 1% treadmill grade most accurately reflects the energetic cost of outdoor running,” Journal of Sports Sciences 14(4):321-327, 1996 (PMID 8887211). Its nine trained male runners ran 6 minutes at each of 2.92, 3.33, 3.75, 4.17, 4.58 and 5.0 meters per second, on a treadmill at 0 to 3 percent grade and on a level road.
- The 2024 study that cut the other way on one machine: Nolè M, Baumann G-A, Spengler CM and Beltrami FG, “Should a 1% gradient be used to equate the metabolic cost between treadmill and overground running?”, Current Issues in Sport Science 9(2), published February 6, 2024. Fourteen highly trained male athletes ran 5 minutes at 14 km/h at 1% on one treadmill model and on a track, and the treadmill runs took more effort. The authors conclude that on that model, 1% added to the difference rather than reducing it.
- How a deck finds its grade: the Trackmaster treadmill manual counts elevation motor gear turns from a calibrated zero, and a Precor service manual follows lift position with a potentiometer. Neither one mentions comparing the deck’s slope with the floor.
- The 98 to 103 percent range: Willwacher et al. (2021), Scientific Reports 11:2244. Across four lab treadmills, one with a badly worn belt and bed, seven participants walking and running left average belt speed between those two figures.
- Indoor pace on a watch: per Apple Support article 105002, the watch tracks indoor runs with its accelerometer.
- The golfer, the 20 yard marker, the 7.9 mph runner and the three belts are made up for illustration, and none of those belts is one I measured.