On most benches, the working surface is somewhere between 33" and 36" high. If you're average height (between 5'9" and 6'0"), that's usually a comfortable height. But even a change of 1" up or down can make a big difference in how easy it is to work at the bench. We've used a lot of methods to determine the best height for a bench. But one simple method seems to give the best results. Just measure the distance from the floor to the crease on the inside of your wrist. Adjust the length of the legs on your workbench so the height of the work surface matches your wrist crease measurement. If you're 5'10" or taller, you may find a wrist crease measurement of 35" to 37". This may seem too high for a bench -- especially considering the old standards. But those standards were developed and valid when the general population was shorter than it is today.
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BTW: The bench in the photo is the Woodsmith Workbench. PlansNOW.com has details.