How to know exactly how many calories you burn per day?

[gbrice75]

How is it possible to know how many calories you burn per day?

I work in metal fabrication and everyday is a different day. Somedays I'll be standing around and not doing much work other days I'll be lifting alot and other days ill be walking a lot and Somedays is a mix of all.

So how is it possible to know exacty how much you burn?

It's really not possible, at least to a science. Firstly, the number is going to be different every day, albeit small changes assuming your activities change very little.

A better question would be "how is it possible to know how many calories I need to maintain my exact weight?". This is still tough to get down to a science, but if you did the exact same thing every day for let's say a month, and ate the exact same diet during that time, you would either gain, lose, or maintain. If you gain weight, reduce calories slightly until you stop gaining. Vice versa if you're losing. Once you maintain, you'll know your TDEE/maintenance calories.

However, it should be noted that THIS number too will change, based on activity and body composition changes. Also, it's unrealistic to assume that activity and diet will be exactly the same, every single day.

[uf21]

It's really not possible, at least to a science. Firstly, the number is going to be different every day, albeit small changes assuming your activities change very little.

A better question would be "how is it possible to know how many calories I need to maintain my exact weight?". This is still tough to get down to a science, but if you did the exact same thing every day for let's say a month, and ate the exact same diet during that time, you would either gain, lose, or maintain. If you gain weight, reduce calories slightly until you stop gaining. Vice versa if you're losing. Once you maintain, you'll know your TDEE/maintenance calories.

However, it should be noted that THIS number too will change, based on activity and body composition changes. Also, it's unrealistic to assume that activity and diet will be exactly the same, every single day.

Exactly my point. I cant do the same thing everyday for a month because I don't work in an office. Everyday I'm doing something different.

So does this mean I can never figure out roughly how much calories I burn per day?

[Phate]

Exactly my point. I cant do the same thing everyday for a month because I don't work in an office. Everyday I'm doing something different.

So does this mean I can never figure out roughly how much calories I burn per day?

you can get an estimate from formulae that are available here, as well as by using indirect calorimetry, i.e. a breath calorimeter though they are still a rough estimate and vary significantly.

Metabolic variability analysis using a mixing chamber-breath by breath based indirect calorimeter and the clino-ortho maneuver.
Cadena M, Infante O, Escalante B, Sacristan E, Rodriguez FJ, Medel LH, Azpiroz J.
SourceDepartment of Electrical Engineering, Universidad Autonoma, Metropolitana, Iztapalapa, Mexico.

Abstract
This work proposes the clino-ortho maneuver to analyze the metabolic energy expenditure variability by Indirect Calorimetry (IC). This analysis uses a hybrid calorimeter which includes simultaneously the mixing-chamber (MC) and the breath by breath (BbB) IC techniques. VO2 and VCO2 short-term variability was characterized as metabolic variability in the MC technique by intra-group standard deviation averages. When the BbB technique was used the metabolic variability characterization was done by VO2 and VCO2 discrete time series power spectrum analysis in the 0-0.5 Hz band. Thus a statistical population of 17 young healthy volunteers was studied using a clino-ortho maneuver with 30-30 minutes in each position after 8 hours of fasting. The results showed an energy expenditure change of 40% in Kcal/day (p<0.01). The metabolic variability was partially significant using the MC technique while BbB total power spectrum changed from 35 to 60 for the VO2 and from 24 to 37 for the VCO2 (ml/bth)(2), (p<0.05) in the region from 0 to 0.04 Hz. It was concluded that using this new measurement technique and the clino-ortho maneuver metabolic variability information not yet studied was revealed.

What about when people say eat x amount less or more (depending on diet) if what you burn is only an estimate and everyday you're burning different amount of calories

when people say that you should reduce your calories by 500/day and you will lose a pound of fat/week they are saying that since a pound of fat=3500cal if you change nothing else you will lose that lb every week