The finding. On flat ground, the ACSM running equation gives a net cost of 1.58 kcal per kilogram per mile at every running speed. For a 160 lb (72.6 kg) runner that is 114 kcal per mile, whether the mile takes 12 minutes or 6. Speed changes how fast you burn calories, not how many a mile costs.
Where the number comes from
The American College of Sports Medicine publishes a set of metabolic equations in its Guidelines for Exercise Testing and Prescription. The running one estimates oxygen use from speed and slope:
VO2 = 0.2 x S + 0.9 x S x G + 3.5
VO2 is in millilitres of oxygen per kilogram per minute, S is speed in metres per minute and G is the grade as a fraction (0.05 for 5%). The 3.5 at the end is the resting part: what your body uses sitting still, also called one MET. ACSM's table converts each litre of oxygen to 4.9 kcal.
On flat ground the grade term is zero, so the running part is simply 0.2 x S. To find the cost of one mile, multiply the oxygen per minute by the minutes the mile takes. Minutes per mile = 1,609.344 / S. The S cancels:
0.2 x S x (1,609.344 / S) = 0.2 x 1,609.344 = 321.9 ml of oxygen per kilogram per mile
At 4.9 kcal per litre, that is 1.577 kcal per kilogram per mile, at any running speed. Speed disappeared from the equation.
What it looks like for one runner
For a 160 lb runner, computed with the same engine as the running calorie calculator:
| Speed | Pace per mile | Net kcal per mile | Gross kcal per mile | Gross kcal per hour |
|---|---|---|---|---|
| 5 mph | 12:00 | 114.5 | 129.4 | 647 |
| 6 mph | 10:00 | 114.5 | 126.9 | 761 |
| 7 mph | 8:34 | 114.5 | 125.1 | 876 |
| 8 mph | 7:30 | 114.5 | 123.8 | 990 |
| 10 mph | 6:00 | 114.5 | 121.9 | 1,219 |
The net column, the calories running adds on top of what you would burn anyway, does not move. The gross column, which includes resting metabolism, actually falls slightly as you speed up, because a faster mile takes fewer minutes of resting cost. The hourly column is the one that rises, almost in proportion to speed: run twice as fast and you cover twice the miles in an hour.
Gross or net: which number is "calories burned"?
Most watches and gym machines report gross calories, which include the 1 MET you would have burned on the sofa. For a 30-minute run that resting part is about 37 kcal for a 160 lb runner (3.5 ml/kg/min x 72.6 kg x 30 minutes x 4.9 kcal per litre). If you are adding exercise calories to a daily total that already includes your resting metabolism, the net figure avoids counting that part twice. The calories burned calculator and the running, walking, treadmill, hiking, swimming and stationary bike calculators show both.
What does change the calories per mile
Body weight
The cost is per kilogram, so it scales directly with weight. Net calories per flat mile from the same equation:
| Body weight | Net kcal per mile |
|---|---|
| 130 lb (59 kg) | 93 |
| 160 lb (72.6 kg) | 114 |
| 190 lb (86.2 kg) | 136 |
| 220 lb (99.8 kg) | 157 |
Hills
The grade term, 0.9 x S x G, does not cancel in the same way per minute, but per mile it also loses the S: 0.9 x G x 1,609.344 ml per kilogram. At a 5% climb a 160 lb runner's gross cost at 6 mph rises from 126.9 to 152.7 kcal per mile, about 20% more. The ACSM equation has no term for downhill savings, so for rolling routes the grade-adjusted pace calculator, built on Minetti and colleagues' measurements of running on slopes, is the better guide to how a hill changes effort.
Walking instead of running
ACSM's walking equation has a horizontal term of 0.1 x S instead of 0.2 x S. Per mile, that is exactly half: 0.789 kcal per kilogram, or 57 net kcal per mile for a 160 lb walker against 114 running. The equations describe different gaits, each within its own speed range (walking about 50 to 100 m per minute, roughly 1.9 to 3.7 mph; running above about 134 m per minute, 5 mph). Between those speeds neither equation is in its stated range, and the treadmill calorie calculator says so when you land there.
Why a faster run still "burns more"
None of this means speed is pointless for energy. In a fixed amount of time, a faster runner covers more miles, so a 30-minute session at 8 mph burns more than a 30-minute session at 5 mph: 495 against 323 gross kcal for our 160 lb runner. If your limit is time, speed matters. If your limit is distance, it barely does.
Limits of the equation
The ACSM equations are estimates for an average adult running steadily on level ground or a treadmill. They do not include air resistance, which grows with speed outdoors, or differences in running economy between people, which can be large. They were built for steady exercise, not intervals. Treat the numbers as a well-defined estimate, not a measurement of your own body; a laboratory test of oxygen uptake is the only way to measure your own cost.
So the useful conclusion is the narrow one: within this standard equation, calories per mile depend on your weight and the slope, not your pace. That is why the running calorie calculator asks for distance first, and why the calorie figures on its results barely move when you change the pace.
Sources: ACSM's Guidelines for Exercise Testing and Prescription, metabolic equations (Table 7.3 as reproduced by Texas Tech University); Minetti et al. (2002), Energy cost of walking and running at extreme uphill and downhill slopes, J Appl Physiol. Rules checked . Found a problem? Tell us.
Questions
Do you burn more calories running fast or slow?
Per mile, about the same: the ACSM running equation gives the same net calories per mile at every running speed on flat ground. Per hour, running faster burns more because you cover more distance.
How many calories does running a mile burn?
About 1.58 net kcal per kilogram of body weight per flat mile in the ACSM equation: 93 kcal at 130 lb, 114 at 160 lb, 136 at 190 lb. Watches usually show gross calories, a little higher.
Does walking a mile burn the same as running a mile?
No. In the ACSM equations, the net cost of walking a mile is half that of running it: about 57 against 114 kcal for a 160 lb person.