Warning: This is a nerdy post that involves math.

In a recent assignment for Active.com, I was tasked with simply laying out how many calories a person could expect to burn doing various types of running workouts. As I did the research for the article, it quickly became clear that there was nothing simple about it at all.

First I examined the variables that can determine the rate of calorie burn for a particular individual, given a particular running workout. Contained within that problem, there are actually two sets of variables – one set relating to the individual’s physical characteristics, and the other set relating to the workout itself. Where the individual is concerned, age, total body weight and body composition are all significant factors, while hormonal influences on metabolism play a smaller, and largely indefinable role. When it comes to the workout itself, pace and incline are the two primary factors, with running surface and wind having much smaller influence.

Since I didn’t want to set up a performance testing lab in my loft, I looked for the best online calculators that could give me a decent average for number of calories burned while running. It turned out that in looking for the best, I had to settle for the least bad. While most web-based activity calculators take bodyweight and running pace into account, it pretty much ends there. I was surprised that none of them used age, which has been shown to be pretty reliably correlated with relative metabolism, and I was disappointed to see that the few that used body composition did so as a function of gender (as a group, women tend to have less muscle and more fat per pound of body weight than men, but individual statistics vary widely). In other words, any online calorie calculator you use is bound to be pretty inaccurate. Using a wearable device or app-based calculator that accounts for more of your personal data, and especially one that uses GPS to track elevation gains during a run, will be much more accurate (but still not perfect).

I couldn’t just write that in the article, though, so I ended up using my favorite online calorie calculator at ExRx.Net to get ballpark calorie burn estimates for a number of different workouts. While that was fun and exciting for me (I’m a numbers nerd, especially where exercise is involved), I was blown away when I clicked on a link below the walk/run calculator that took me to this Walking and Running Energy Efficiency Page. If you hate charts and graphs with statistical dots, you don’t have to look at that page. What it says is simple to understand and hugely gratifying for me, since I have been saying it to my clients for years:

Running burns way more calories than walking does.

“Duh!” you’re thinking. But that’s because you didn’t look at the chart/graph. Running at the same speed as walking burns up to 70% more calories. If a person walks at 3 miles per hour, he or she burns roughly 52 calories per mile per 100 pounds of body weight. However, if he or she jogs at that blindingly slow pace, the calorie burn increases to 89 calories per mile.

And here’s something I was really shocked to learn: Although walking faster increases the number of calories burned per mile, running faster has the opposite effect. Yes, the slower you run, the more calories you burn per mile. The reason why is that it’s so inefficient for your body to jog at a slow pace, but that efficiency improves as you run faster and faster. For those who want to lose weight, this adds new fuel to my argument about Why You Should Run Really Slow.

Note that the “per mile” bit is important, though. If you only have twenty or thirty minutes to get in a workout and you want to maximize calorie burn, then running as fast as you can during that time will burn the most calories (because you’ll be covering much more distance than if you run slow). However, if you’re going to log two or three miles on a Sunday afternoon, you’ll actually be doing yourself a favor (calorically speaking) by throttling back to the slowest possible pace you can keep and still be jogging but not walking. Here’s a little math to illustrate the different options you have:

You weigh 200 pounds (keeping it simple for math purposes)
You walk at 3 miles per hour for one hour = 3 miles
3 miles X 52 calories/mile X 2 (this is the weight factor) = 312 calories burned

You jog at 3 miles per hour for one hour = 3 miles
3 miles X 89 calories/mile X 2 = 534 calories burned

You run at 6 miles per hour for 1/2 hour = 3 miles
3 miles X 81 calories/mile X 2 = 486 calories burned

You run at 6 miles per hour for one hour = 6 miles
6 miles X 81 calories/mile X 2 = 972 calories burned

So, you can see that you burn many more calories per minute by running faster, but not per mile. It really just depends how fast you are willing/able to go and for how long.

If you hate jogging, no matter how slow, or you have some physical limitation that doesn’t allow it, then you can still get a really good calorie burn by walking, as long as you push the pace. Adding an incline will also increase calorie burn a significant amount, but if there’s a choice between going faster or going uphill, you can probably squeeze out a few more calories by maxing out your pace over flat terrain than walking or jogging more slowly uphill.