Do you mean that the diameter is 50"? If so it will be plenty, but for such a shallow curve I think you could get away with regular (non-bias) binding around the outside and on the way in/out of the center, and just use bias on the inside edge.
Here's a handy site to calculate how much you need. For a diameter of 50", your circumference is about 157, and you need another 50" to get in and out of the center, plus something around the center - say 15", depending on how big the center is. Add some fudge factor and you might need 230" or thereabouts. The chart says that your half yard will make 296", so you will have plenty.
http://www.generations-quilt-pattern...s-binding.html