Calculating Calories Burned

by Charlotte on January 25, 2008 · 10 comments

Alex asked me an interesting question in the comments, namely: How can I calculate my calories burned during a workout? Can I do it if I know my heart rate (from wearing a heart rate monitor)?

Well, Alex. That is a very good question with a very long answer. Hence, a whole post – just for you! Everyone else feel free to close their ears. Unless you have more info on this subject than I do (Andrew? You out there??) – then, by all means, SHARE!

Calculating Your Basal Metabolic Rate
Your BMR, otherwise known as how many calories your body burns just to survive (so not counting exercise), is the place to start. You have to know how many you need to know if you have a deficit or not.

The only really accurate way to calculate this is to pay a lot of $$$ and get a metabolic testing done (they offer these, with varying accuracy, at many gyms nationwide). The next best thing is to use one of the BMR formulas. There are three main ones, with the Katch-McArdle being the most accurate (but you have to know your lean muscle mass, derived from your body fat %). Tom Venuto, one of my heroes & my first real introduction into nutrition and fitness, puts it much better than I can. Check out all the formulas here.

If you are bad at math, or just lazy, here’s a quickie calculator for you.

Calories Burned in Exercise
This is what Alex was asking me. How to tell how many calories you burned during exercise? If you have a heart rate monitor that does this for you, then the only trick is figuring out how to use said heart rate monitor (which can get your heart rate up just by reading the friggin’ manual). You should know that each heart rate monitor (whether it be on your wrist or on your elliptical) uses a proprietary formula to calculate calorie burn based on, at minimum, your weight and heart rate. The good ones will also factor in your gender, height and age. Each company (Polar, Timex etc.) has their own formulas they’ve developed and they’re not happy about sharing them. Probably because someone would actually do the math and realize that they are overestimating your calories for material gain. Ahem.

So, what’s a fitness fiend to do? There are plenty of online calculators that will estimate your calorie burn based off of type of activity, weight, duration and perceived exertion. I particularly like the one on

You will notice though that there is nowhere to put in your heart rate, even if you know it. This is because your heart rate is constantly changing during your workout and so this information isn’t helpful to you in this context. Even if you know your average heart rate, the formulas are already based on averages so your won’t be so much different. You can use your heart rate though to gauge your perceived exertion over time.

Hope this helps, Alex! If any of you have anything to add- please jump in!

{ 10 comments… read them below or add one }

Alex January 25, 2008 at 3:38 am

After I posted the question, I rifled through Google some more and found this link:

Which explains it in terms of max heart rate and VO2 max. I understand what you were saying about the complexity involved (and a pox on those companies for their secret formula-keeping) – but I’ve never been overly impressed with the online calculators as a substitute. They don’t overestimate nearly as much as cardio equipment does, but I always tend to not believe the answer (as too high). I think I might try to use my average heart rate from my run tomorrow with the chart from that link and see what kind of ballpark that gives me. Perhaps I will remain unsatisfied still. Perhaps not. Perhaps I will upgrade to a fancier HRM next year. Perhaps I should get a new hobby.

Thank you for the response! As you may have guessed, I love the blog. :)


Josie January 25, 2008 at 5:43 pm

Hey Charlotte–

I tried the 8/12 sprints today. Since that study said that they started with 5 min, I made 5 min of my cardio this morning 8/12 sprints, just to try it out. I used the bike on your rec, and I did it towards the end of my cardio (like 30 minutes into a 40 min session).

I don’t usually use the bike (I’m a stair mill girl), so this was an adjustment for me, and figuring out the right level and set-up was kind of tricky in itself. I think I had it too low because my knees were hurting after a few minutes.

My heartrate didn’t go crazy during the sprints. I liked the format of it though– changing it up so often was good, and the burst-then-active-rest is good for my own training (I play roller derby, so I’m skating 3-5x a week– this is in addition to that).

I’ll definitely try them again and plan to work it into my schedule.

Thanks for the tips!



thejulia January 25, 2008 at 8:21 pm

i also tried the 8/12 sprints (also only 5 minutes) and I love it. I’m going to slowly work my way up to 20 minutes. I can’t believe you reversed it.


Natalie January 26, 2008 at 12:18 am

thanks for the info! it’s crazy how much those reports say the machines overestimate, one thing i also read that i thought was really interesting was you think when you go burn 500 cals or whatever you have to also subtract the calories you would be burning if you weren’t working out during that whole time. It also bums me out that the more you routine your work out becomes the less calories you burn haha. love the blog =)


Charlotte January 26, 2008 at 8:57 pm

Alex – Ooooh cool! Let me know how it works for you!! And hey – if you need a new hobby, I do too;)

Josie – Rollerderby!!! Nice:) Yeah, the sprints should make your heart rate skyrocket. Maybe try upping the intensity level? Do you have access to a spinning bike? They’re easier to sprint on that the normal gym cycles. Also you could try reversing them (sprint 12 seconds, actively recover 8).

Thejulia – glad you liked ‘em! Yeah, I felt kinda dumb after I realized my mistake. Def. a killer workout.

Natalie – Welcome!! So glad you like it here! I hope you stay:) Yeah, I’ve heard that about subtracting the cals you would have burned just sitting around. Except for me I use the cals burned more as a gauge of my exercise intensity rather than the actual number value. My watch is way off anyhow!


Brendon March 1, 2008 at 6:11 am

Here’s some propriotary info for you…

I came across a posting from someone with the same confusion.

He emailed the company (he didn’t specify) who makes his HR monitor and asked them for the calculation behind the calories burned, here’s what they gave him:


HR = Average Heart Rate for workout
W = Weight in KG
T = Time of workout in minutes

(You can copy that into Excel and substitute your values.)

Plugging in the numbers from a few of my workouts, gives pretty much the same calories burned as my TIMEX watch.


Charlotte March 2, 2008 at 3:14 am

Thank you Brendon!! How much do I love math?? Seriously, you just made my whole night. Now I have to go fuss around with it. It doesn’t factor in gender though and that makes a big difference when talking about calorie burn. I have a timex watch too…


brian October 14, 2008 at 2:50 am

Heart rate monitors aren’t as accurate because they don’t take into account how many different muscles are being worked during exercise. For instance, some exercise bikes have moveable arms, some don’t. A person will burn many more calories on an exercise bike if he is working his arms and chest at the same time he is moving his legs, even if his heart rate is the same as when he rides a traditional bike with no moving arms.


TB August 10, 2013 at 6:20 pm

The calorie calculator on is the one you particularly like? Where you enter your bodyweight, an activity and duration, and it states “you burn X calories” with a specific value right down to a decimal place… with no explanation that actually this is a very generic and inaccurate estimate. They’re no right stating the figure with that level of precision – it’s absurd!
Recommending that calculator in your post really devalues the rest of what you’re saying, especially when you are talking about the (im)precision of other methods!


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