Treadmill calculator: speed and incline to outdoor pace
On a treadmill, the equivalent outdoor speed is calculated with the ACSM running equation, counting a 1% incline as making up for the lack of wind (Jones and Doust, 1996). Enter your treadmill speed and incline, and the tool gives you the speed and pace on flat ground, outdoors, that take the same effort.
Fill in the fields to see the result.
How to use it
- Enter the speed shown on the treadmill (in km/h or in mph).
- Enter the treadmill incline, as a percentage.
- Read the equivalent outdoor speed and pace, on flat ground.
- To match an outdoor pace on a treadmill, adjust speed and incline until you hit your target pace.
The method
The ACSM (American College of Sports Medicine) running equation estimates oxygen consumption: VO2 = 0.2 x speed + 0.9 x speed x grade + 3.5, with speed in meters per minute and grade as a fraction. The first term is the cost of moving forward, the second the cost of climbing. On a treadmill, there's no air resistance: Jones and Doust (1996) showed that a 1% incline is enough to make up for it.
So the calculator takes 1% off your incline, then finds the outdoor speed on flat ground that costs the same amount of oxygen. Simplifying the equation gives: outdoor speed = treadmill speed x (1 + 4.5 x (incline - 1%)). At a 1% incline, both speeds are equal; above that, the outdoor effort matches a higher speed; at 0%, a lower speed.
An example
You run at 12 km/h (5:00 per km). At a 1% incline, the outdoor equivalent is 12 km/h. At 0%, it's 12 x (1 - 0.045) = 11.46 km/h, or 5:14 per km: the flat treadmill is a bit easier than outside. At a 3% incline, it's 12 x (1 + 0.09) = 13.08 km/h, or 4:35 per km.
Limitations
Jones and Doust tested trained runners on 6-minute efforts, between 10.5 and 18 km/h: the 1% rule is less reliable outside that range, and other studies have found less clear-cut results. The ACSM equation applies to running (above about 8 km/h, or 5 mph) and to uphill: it doesn't work downhill. It describes an average runner, not your own running economy, and it doesn't see the heat of the gym, which raises your heart rate without changing your pace. Finally, the speed shown on some treadmills isn't accurate: if your watch and the treadmill disagree, it's often the treadmill that's wrong.
Frequently asked questions
Should you set the treadmill to a 1% incline?
To match the effort of running outside on flat ground, yes: Jones and Doust (1996) showed that 1% makes up for the lack of wind, at speeds from 10.5 to 18 km/h. At 0%, the treadmill is a bit easier.
Is running on a treadmill easier than outside?
At the same speed and with no incline, a little, because there's no air to push through. But the heat of the gym and the monotony often make the workout feel harder.
How do you convert mph to km/h?
Multiply by 1.609. 6 mph is about 9.7 km/h, and 7.5 mph about 12 km/h. The calculator does the conversion for you.
Why doesn't my watch show the same pace as the treadmill?
On a treadmill, your watch estimates pace with its accelerometer, without GPS, and the treadmill may be poorly calibrated. Rely on one of the two instead, always the same one, and on your heart rate.
Sources
- Jones A.M., Doust J.H. (1996). A 1% treadmill grade most accurately reflects the energetic cost of outdoor running. Journal of Sports Sciences, 14(4), 321-327.
- American College of Sports Medicine (2021). ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. Wolters Kluwer.
What if ELYO worked it out for you?
ELYO reads your treadmill workouts just like your outdoor ones, compares your effort through your heart rate and adjusts your paces and your plan from your real data.