Btu Calculator 3.1 I Need A Formula For Working Out Btu For Rooms, Including Out Side Walls Etc, Not A Calculator, A Formula?

I need a formula for working out btu for rooms, including out side walls etc, not a calculator, a formula? - btu calculator 3.1

Sorry, you need a computer.
They should at the surface of the walls white (and its R-value)
Sunlight, the size of the window (and its R-value,
and) leaks at the perimeter, ceiling and floor
Gains or losses), and a lot of internal heat.
There simply is not (right), simple solution.