What the flat equivalent shows
The same pace feels harder on an incline than on flat ground. The flat equivalent converts speed and incline into the flat-ground speed that produces the same effort. The calculator uses the American College of Sports Medicine’s metabolic running equation: VO2 = 0.2 · v + 0.9 · v · grade + 3.5, with v in metres per minute and grade as a fraction (5% = 0.05). The resulting VO2 demand is converted back into the speed that would produce it at zero incline.
Energy use per hour
From the oxygen demand (VO2 in millilitres per kilogram per minute) and body weight, energy use can be estimated using the approximation of 5 kilocalories per litre of oxygen consumed, also from the ACSM guidelines. The result is an estimate for a steady pace without breaks, not a measurement from metabolic cart testing.
Example: 10 km/h at 5% incline for a 70 kg runner gives about 931 kcal per hour, versus about 774 kcal per hour at the same speed on the flat.
The 1% rule for missing air resistance
A treadmill removes the air resistance you push against outdoors. A commonly cited rule of thumb suggests setting a 1% incline to compensate. This rule comes from a single study on a small group of fast runners at speeds close to elite marathon race pace, roughly 3:30 to 4:00 min/km (Jones & Doust 1996, Journal of Sports Sciences 14(4), DOI 10.1080/02640419608727729). At slower recreational paces the effect of air resistance is much smaller, and the 1% rule is debated in sports science. Easy-paced runners do not need to add the incline for this reason.
Limits of this calculation
The ACSM equation applies to running, not walking, and is validated for speeds above about 8 km/h. Individual running technique, cadence and the cushioning of the specific treadmill also affect real energy use. The figures here are estimates from a general formula, not a replacement for metabolic testing.
Frequently asked questions
What flat-ground pace matches 10 km/h at 5% incline?
Using the ACSM running equation, that is a flat equivalent of about 12.25 km/h, a pace of roughly 4:54 min/km rather than the 6:00 min/km shown at 10 km/h.
How many calories do I burn at 10 km/h with a 1% incline?
For a 70 kg runner that works out to roughly 790 to 800 kcal per hour, depending on exact weight. Enter your own figures above for the precise number.
Do I always need to set a 1% incline on the treadmill?
No. The 1% rule was studied at very fast speeds close to elite marathon race pace (Jones & Doust 1996). At an easy training pace the missing air resistance barely matters, and the rule is considered debated in sports science.
Why does the same pace feel different on a treadmill than outdoors?
On a treadmill the belt moves the ground under you, while outdoors you push yourself through air resistance and over changing terrain. Both change the real effort at the same displayed pace.