Calculating square footage for a patio project

September 1, 2005 10:55 AM

I'm working on a patio project at home, and I'm trying to calculate the square footage of an area that's in the shape of an irregular pentagram. It's about 19ft 6 inches long at it's base, and then has measurements of 70", 93", 43", and 16ft (192in). Is there a utility online I can use to calculate this area, or possibly a feature in Visio that I can use to do this with? Many thanks in advance for any time you take to post.
posted by DCTapeworm to home & garden (4 answers total)

Subdivide the area into triangles, work out their area seperately. Simple trig.

Don't think you've given us enough information to work out the area for you, but I'm probably about to be proven wrong.
posted by Leon at 11:04 AM on September 1, 2005

Area of an Irregular Polygon, googled easily enough with irregular polygon area sides
posted by sonofsamiam at 11:19 AM on September 1, 2005

We don't have quite enough information. Here's one way to think about why. Imagine a pentagon with some fixed side lengths, built out of drinking straws connected with flexible corners. If you picked such a thing up off the table, it would be all floppy -- the side lengths alone aren't enough to dictate the shape and thence the area. (Note that this isn't true with a triangle, which is why Heron's Formula works.)

If you know the angles involved, here's how to get the area. If you know some other information (like the "coordinates" of the corners), check here.
posted by gleuschk at 11:22 AM on September 1, 2005

All those suggestions will give you the exact answer, but if the need for area is in terms of purchasing materials, and you can get a little extra, I recommend that you just divide the area into squares/rectangles or right angle triangles, and add up the results of these easy formulas (length x width for squares, and length x width/2 for right angle triangles).
Quick and easy, and you should be very close to the 'exact' answer.
posted by extrabox at 6:10 PM on September 1, 2005