Calories burned / tracker?

This link has got MET rates for various activities.

https://www.healthline.com/health/what-are-mets#examples

Sitting 1.3 MET to Running 7mph 11.5 METS
We also need the MET count for breathing and sleeping.

I am fairly sure I could leave a fitbit on the desk and at the end of 24 hours it would say I had burned 1800 calories.

But based on the above we could use the heath app steps recorded per hour as a proxy for the level of activity and calculate METs from that.

I am just doing a back of the envelop calculation below, to see if the answer makes sense.

7 MPH is 11.5METS
7 miles => 11265m => 11265 / 0.75 = 15020 steps in 1 hour

Where 0.75 is my stride length (can be approximated from height for the person)
There is a formula somewhere for that, need to find it.

0 steps -> 15K steps in 1 hour
1.3 to 11.5 Mets
So that transcribes to a rate of

(11.5 - 1.3) / 15020 ==> 0.000679 MET per step per hour.

So say I do 2K steps in 1 hour
My MET rate would be 2000 * 0.000679 => 1.358

So I walk 6000 steps in 1 hour => 4.074 METS

I am 80KG

Total calories burned = Duration (in minutes)*(MET*3.5*weight in kg)/200

=> 60 * 4.074 * 3.5 * 80 / 200 => 342 calories

RESULT: Thats a believable answer !!!!

So I think we just need the background constant METS for being alive.
Is it 1.3 (the sitting at a desk value or 1 ?).

QUESTION: Lets calculate 24hours of no exercise (ie no steps)

Total calories burned = Duration (in minutes)*(MET*3.5*weight in kg)/200
Lets try a MET rate of 1.

=> 24 * 60 * 1 * 3.5 * 80 / 200 => 2016 (ooh that is close to 1800 cals).

If we use a MET rate of 0.9 as the sleep value we get 1814 cals. Which is very close to the fitbit value of calories burned when you leave it on the desk for 24 hours.

So I think we have a way to calculate this.

Ideally we would just add this into the Health app and add a setting in the Health App to Age Height (to work out stride length) and Weight in KG.