No, you should measure the interior space.
That depends on why you need the square footage. For building permits, tax assessments, etc. it is the outside; for floor covering of course the inside...
If your wanting the entire square footage you can measure the width and length of your home from the outside. If your wanting to know the square footage of the heated space, measure each room width and length that have air ducts. Multiply the width and length measurements.
First of all, you need to know the radius of the tank. Second, what does outside square footage mean?
The Sound Transmission Class (STC) rating of the windows in this building is a measure of how well they reduce sound transmission from outside to inside.
This is one case where the common usage in English has eliminated the proper descriptive function of a preposition. If something is "outside a building", it is actually outside "of" the building, but the word "outside" creates an adverbial clause that removes the need for the "of". "He was standing outside the building." (same case for "inside") The "outside of a building" is a noun meaning the exterior wall. "I had to repair the outside of the building."
Depending on what you need the information for, you can get a rough idea by measuring the entire outside of the house. Then multiply the length of the house times the width of the house, and then double it. That will give you a very basic idea. If you need the exact square footage, you could purchase a copy of the blueprints from the building department.
The Average outside air Rating of most Commercial Buildings is a min. of 15% exchange of your total cubic air space, per Hour during Occupied time period's.
With a tape measure. You asked. Outside to outside, top to bottom.
Living footage is to the outside of the walls.
House dimensions are measured in Square Feet. How many square feet are in a house depends on the size and the layout of the house. For example, many houses do not have equal footage of all outside walls. Also, square footage of each room is smaller that the footage of outside walls, to subtract for walls, fireplaces, etc. Also, any outdoor additions (porches, patios) are not counted in sq. footage of the house.
outside to outside
Air will flow out of a building when the outside temperature is warmer.