I believe 42 in. is the standard, but it's your bar so build it as high as you wish. Test the height out prior to the build. See if you/your guests would be comfortable sitting at a bar top of that height, standing would would be less of an issue.
42 inches. Go out and do some field research. Bring a tape measure. I assume you're designing this on your own? You'll pick up a lot of ideas for the little details from commercial bars. I had an absolute blast when I built mine a few years ago. By far, the most enjoyable home project I've ever done! (not counting child rearing, of course)
42" is the "bar height standard" that I had found doing some of the same research. There is also "counter height" which is lower.
