Now here's a clever idea for an app: using the position sensors in your iPhone, the free RoomScan app creates a pretty accurate floor plan (within a foot or so) of any room.
When you launch the app you'll see some help screens, and there are links to several videos showing RoomScan in operation. To get started, you just touch your iPhone to any wall. Walk to another wall and tap the iPhone on the wall, and then go to another. When you have touched all the walls, go back and touch your original wall, then tap the 'finish' button. RoomScan then draws a reasonably accurate floor plan. The app guides you by voice in what to do, and it if feels it doesn't have accurate data it will ask you to repeat the process. If you bring your iPhone or other iOS device to to the wall with a jolt, RoomScan says "ouch!" and asks you to try again more gently. You also need to move fairly quickly between walls, or RoomScan asks you to pick up the pace.
I didn't have much hope that any of this would work. I tried it in my master bedroom, which has a bay windows and some angled walls, and the resulting diagram was quite close. In the app's settings, you can select US or metric measurements. Your floor plan can be emailed, which is very handy. A paid version of the app lets you add symbols for things like doors, and connects multiple rooms so you can create a whole house floor plan. The Pro version is US$4.99
I continue to be amazed at some of the helpful and really creative apps that have appeared for iOS, and RoomScan and RoomScan Pro are each a case in point. I wouldn't use either app to create architectural plans that have to be super-accurate, but RoomScan does what it claims to do. Try the free version to convince yourself that it works, and if you want more, go for the paid version.
RoomScan is a universal app. It requires iOS 7 or later and it's optimized for the iPhone 5. It's useful, and it's is also a great demo of what iOS 7 can do.