A 150-pound man burns 100 calories per mile; a 200-pound man burns 133 calories per mile; and a 250-pound man burns 166 calories per mile. You burn virtually the same number of calories whether you run or walk a mile; you just get there faster if you run. See below for a chart of calories burned during walking at different speeds and body weight.

How can people measure steps and calories burned during exercise?

Smartphone apps and wearable fitness devices are all the rage. But are they accurate?

Estimating calories burned

Recent research shows that wearable activity monitors can be in error anywhere from 9.3%-23.5% in detecting how many calories you burn during your workout, with the average error being 12.9%. This means that if you were to burn 300 calories during your workout, your device could be inaccurate by about 39 calories. But the error could be far greater because measuring calorie expenditure in a laboratory where the temperature, humidity, and terrain (studies are conducted on treadmills) is held constant is much different than outdoors where the weather can make a big difference in how many calories you burn and so does what you wear. For instance, you burn more calories...

when the temperature is cold compared with hot because your body works harder to keep you warm, when it's humid and warm than dry and cool in an attempt to stay cool, when the terrain is hilly than when it's flat because it requires more energy to climb hills, when you wear heavy, restrictive clothing compared with workout gear.

Wearable fitness devices and smartphone fitness apps are smart, but not that smart. They don't add the above factors to the calculations that help them estimate how many calories you burn. One could argue that if the error is constant then you can use the device as a method of determining whether you burn more or less calories from workout to workout. That argument has merit, but I don't recommend deciding how many calories to eat if you want to lose weight based on how many calories the device tells you to burn. For example, if it says you burned 600 calories working out and you figure you can splurge on ice cream as a treat, well, that's all well and good, but what if you really only burned 500 calories and the ice cream is 600? You won't lose weight that way. But aside from that, I like the idea of the feedback from devices, even if there is some error. Just don't count on the calorie burn estimate as a precise way to decide how much to eat if weight loss is a goal.

Estimating steps

Smartphone apps and wearable devices are more accurate at estimating steps than they are at estimating calories burned. They use sophisticated accelerometers, or motion sensors, to count the steps. Interestingly, recent research shows that smartphones were often more accurate than wristbands. Smartphones were off by -6.7% to +6.2% whereas wearable devices were off from -22.7% to -1.5%. Pedometers and accelerometers were most accurate with error of just 1.0% or less.

What does it all mean? Don't throw out your devices! Even if there is error, they still provide feedback which research suggests can motivate you to be more active. And if the error is consistent, then at least it's going to tell you whether you did more or less from workout to workout. And they're fun, I say wear them and enjoy them!