Three shapes, one unit
Everything on a survey sheet is one of three things. A long joint is a length times a width: sixty feet of quarter inch soffit joint is 60 x 12 x 0.25 = 180 square inches. A round hole is pi over four times the diameter squared: a 4.5 inch dryer penetration is 15.9 square inches. A rectangular opening is width times height: a 14 by 20 louver is 280. Once all three are in square inches they can be sorted, and until they are they cannot.
The list is not flat
On the default list — seven lines, thirteen openings — the total comes to 1,508.5 square inches, which is a square a little over 38 inches on a side. Two lines carry 71% of it: the pair of gable louvers and the four crawl space vent frames. The two round penetrations, which are the ones people notice and point at, carry 1.3% between them. That is the usual shape of the answer.
It matters because material follows the ranking or it gets wasted. A roll of mesh spent on the two largest lines removes most of the measured area; the same roll cut into small patches for the smallest six lines removes almost none of it. The survey is worth doing precisely because the intuition about which opening is big is wrong so often.
What this page will not tell you
It gives no mesh size, no gap threshold and no opinion about what any animal can pass, and it names no product. Those are supplier and state extension questions, and the answer changes by species and by region. What it does is arithmetic on the numbers you measured.
Related pages
Once the ranking says where the material goes, the vent screening take-off turns the vents and louvers into mesh, rolls and fixings, the caulk calculator turns the linear feet into cartridges, and foam coverage handles the static gaps. For the round holes with a pipe in them, the penetration annulus page is the one that has the geometry. For doors and windows, the weatherstrip calculator does the same open-area sum along a moving joint. If the fan test figure is what you are chasing, the leak area calculator converts a reading into an area, and the home energy audit guide puts a survey in order.
Questions people ask
What units do I use in each column?
They differ by kind, because that is how the measurements arrive. A run is a length in feet and a width in inches, since a joint is paced out and its width is read off a gauge. A hole is a diameter in inches. A rectangle is width and height in inches. Mixing them up is the one mistake that shows immediately: a 60 in the width column of a run turns a soffit joint into 43,200 square inches and it will sit at the top of the ranking looking obviously wrong.
Why does the running total column matter more than the individual shares?
Because it answers the question you actually have, which is how much of the list you can ignore. If three lines out of seven reach 83%, the other four are a rounding error against the effort of getting to them. The threshold field lets you move that line — set it to 50 and you usually find one or two openings carry half of everything.
Should a screened vent be counted as open area?
That is your call and the page does not make it for you. A louver with intact screen behind it is not an open hole, but it is also not sealed, and if the survey is about a different problem than the screen was installed for it may belong on the list at full area. What the page will not do is apply a factor of its own, because the factor depends on what is behind the opening and on what you are surveying for.
Why does the survey total not match my blower door number?
They are not the same measurement. An equivalent leakage area is derived from flow at a test pressure, so it counts only paths that actually move air and it includes every path you never found. A survey counts the geometry of what you could see and measure. A survey total well under the fan test figure usually means the leaks are in places you did not walk; one well over it usually means several of the openings are blocked or baffled behind.
Does this page tell me what to seal or how?
No. It converts measurements to area and sorts them. It gives no mesh specification, no gap size, no method and no product, and it says nothing about animals, because the moment a page like this starts naming what fits through what it is making a claim it cannot support. The material take-offs are separate pages, and anything involving an animal that is already inside a building belongs with a licensed wildlife control operator and your state wildlife agency.