First short on what basal metabloic rate (BMR) is.
BMR is the amount of energy (like kJ or kcal) that we spend when we rest. And with rest we mean that the digestive system is inactive to, wich mean after about 12 hours of fasting. So even if you don’t move a bit you will spend energy on keeping your heart, brain and other organs alive and in function.
I made a test in school to see what my BMR is. I’m gonna make a little explanation on where the numbers come from and give you a shourtcut.
1. Count how many times you breath in one minute. To get a more accurate result, do it a number of times and use the average number.
Example: I breath 10 times a minute.
2. If you can get hold of a measuring instrument to measure the volume of your normal exhalation, the resulte will be more exact. Otherwise you use 0.5 liter air wich is the average for mose people. Multiplicat the liter with how many times you breath a minute.
Example: 0.5 liter * 10 times = 5 liter a minute
3. Multiplicat so you get a number for how much air you use a day.
Example: 5 liter * 1440 (hours of the day) = 7200 liter air/day
4. In the air we inhale it’s approximitly 20% oxygen and in the air we exhale it’s 16%, so we use that 4%. Take 4% of the answer in number 3 and you get how much oxygen you use each day.
Example: 0.04 * 7200 = 288 liter oxygen/day
5. Now multiplicate with 21 and you get your BMR in kJ.
Example: 288 * 21 = 6048 kJ
6. To get it in kcal, divide with 4.2.
Example: 6048 / 4.2 = 1440 kcal/day
There’s the info for the mathematic interested. ( ^3^)/
Here’s if you don’t like math: Multiplicate your breathing/minute with 144 and you get your BMR in kcal. I’m not giving an example for that one.. (‘_´)
I’m not sure about how good this method is.. It says nothing about weight, sex or age, only how much you breath..
A classic way to calcurate your BMR is the Harris-Benedict equation, that you can find here: http://en.wikipedia.org/wiki/Basal_metabolic_rate#BMR_estimation_formulas There can you also find the newer and better method developed by MD Mifflin and ST St Jeor.
Summary for me
Air method: 1440 kcal
Harris-Benedict: 1440.5 kcal
Mifflin-Jeor: 1325 kcal
Remember that this is for 24 hours if you do nothing. If I would do something for an hour that burns 150kcal/hour, the total amount burnt for me that day is 1325 / 24 * 23 + 150 = 1420 kcal