iPad scale drawing app

Use excel or spreadsheet program of some sort. Make the cells square. Each cell = 1" (or 6" or whatever resolution you need)

http://www.indeeo.com/idraw/ can draw things to scale -- it's basically a graphics app, kind of like a simplified Illustrator. I use it on the Mac and find it quite handy, though I haven't tried the iPad version.

Not to threadsit, but to add a tiny bit of detail that might help, one of the main problems I've had in the past is that I'll have a space shaped http://imgur.com/Z4otkQE (ok, that's a bit of an exaggeration, but not that much). Actually measuring those angles is hard and time consuming, so I'd like something where I can measure the sides, as well as the sides of the pieces inside, and their distances from each other, and it will figure out the correct angles to make it all fit together right. I've found doing this manually to be very error-prone. I don't think something super simple like a spreadsheet is going to cut it. I'll check out those Sketchup alternatives as well as iDraw. I'm also playing with some CAD apps to see if those work for me. I'm pretty good at picking up complex software, so it doesn't need to be braindead simple, but I do want something that will do at least some of the work for me. And I'm quite willing to spend some money on a great solution, but $1500 for a professional app (yes, I found one like that) is a bit much. I could see spending $100-200 for a really awesome app, but I'd need enough information to avoid it being a complete leap of faith. Worst case I can use OmniGraffle or Sketchup on my computer, but in the past I didn't find either of them to really solve the "a bunch of weird angles to figure out" problem. Maybe I just haven't learned them well enough yet. FWIW, the main reason I want to use the iPad and do the scaling in real-time is so that I can notice immediately if I made an error or forgot to measure something important. In the past I've spent a ton of time writing down measurements on paper, then hours later go to enter it into the computer only to realize I screwed something up... Thanks everyone.

where I can measure the sides, as well as the sides of the pieces inside, and their distances from each other, and it will figure out the correct angles to make it all fit together right I might be misinterpreting, but note that geometrically, this is impossible with anything with 4 or more sides. If you break it down into triangles (i.e., measuring from corner to corner), or a conjunction of rectangles, any of these apps should be able to do it.