Most textbooks list the "normal" adult capacity at somewhere between 400-800 cc. I believe what it meant by this is the volume at which the involuntary urination reflex is triggered -- which means that, in most cases, one could force oneself to hold somewhat more than that, but they would have to concentrate consciously on holding it in from then on. I think how much you can finally hold before urinating involuntarily may depend on your pain threshold as much as anything else, although some people do have weak sphincter muscles and literally can't hold it for that long. As another answer stated, most people typically first feel the urge to go at 250-300 cc.
In practical experience, this seems to vary a lot from person to person, especially as some people make it a habit of emptying the bladder as soon as they first feel the slightest urge, while others routinely hold on for much longer than that until their bladders are stretched way out (think nurses, teachers, etc!). Repeated "stretching out" over time can increase the functional capacity of the bladder -- which means that a person who routinely holds it in for a long time will probably hold more, on average, than one who generally "goes" at the first sense of need. However, holding urine too long can sometimes lead to bladder infections or even to difficulty emptying the bladder properly, as is most frequently seen in men with prostate issues. In those cases there may be 1000 cc or more of fluid actually in the bladder, but maybe only 200-300 cc can be voided at a time, so the person may have to urinate very often. So, I guess the answer depends partly on what you mean by "holding" urine... but even so, it seems to vary quite a lot.
anatomy/physiology texts and personal experience...