I've seen a lot of people talk about building their own, and I know you can build a rudimentary stand for next to no money, but I will throw this out there. Between lacing my own wheels for older bikes, and tuning up newer bikes to flip, I decided to go out and buy myself a wheel truing stand. I got one for around $60 from Performance Bike. Yes, you will have buyers remorse after unboxing it and looking at it, thinking " I can't believe I just spent that much money on this", but, truth be told, even the cheap ones are well designed, and have features that make it much easier to true any wheel you can throw at it. For instance, the one I got has arms that adjust in and out, to accommodate any wheel thickness, front or rear. Yes, you can make a stand out of a front fork, but you can't fit a wheel with a 7 speed freewheel in it. On the other hand, if you're lucky enough to have a frame with dropouts on it that you can cut up, you can use that, but you still need some sort of spacers to put in if you want to do a front wheel. The store bought ones have feeler gauges that swing right into place and are easy to adjust, and scales for runout that are easy to see. You will get tired of re-bending paper clips all the time eventually. If you have a dial caliper with a base you can use that, but if you don't you'll spend almost as much money on one of those.
I had real apprehension about dropping even $60 on one, but once I did, I use it all the time, and I don't ever have to go scrounging around the shop for some weird part to make it work. They are overpriced based on what it costs to produce one, but they really do the trick.
Oh, to answer your original question, a little over half of 29 inches...
