Here's another great post from fellow Autodesk Support Specialist Chris Aquino - thanks Chris!
Recently I had a few cases where the quantities in Parts (and Wall) schedules show unexpected amounts. During my research, I made a few of these schedules and saw the same results. At first I confused (I was petrified) as the numbers were not jiving. But I said to myself "You were a Mathematics major for two years, you should be able to figure this out!"
After a little bit of futzing around (with some help from the Revit UI), I was able to figure it out. Basically, if you measure the full width of a box with walls 3 inches thick in two directions, then count the volume, the volume of the material (3 inches) at the corners would be counted twice.
What Revit does is that it uses the average dimension between the shortest dimension and the longest dimension in the formula to calculate the area. Or in cases of 90 degree corners, it takes the full width minus half the width of both corners. The new way that 2012 displays highlighted elements really shows this:
The math breaks down as such:
Brick (outer layer):
21'- (1.5" x 2) = 20'-9" (where 1.5" is half the thickness of the brick)
20'-9"= 20.75'
20.75' x 10' – 207.5' sqft.
3" = .25'
207.5' x .25' = 51.875 cuft.
Click here for a video showing the math and results.
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