I’ve found that a lot of furniture proportions can be derived directly off the body, and most often can have a handspan as the common factor/module. For example, typical working counters are half your height (4 hand spans) and an arm deep (3 hand spans). Chairs are 2 handspans high; a step stool is one and so forth. Dining tables stumped me though. Best I could come up with his one hand width (not span) above your navel when sitting down. Not very precise, though—too many variables I think. The other night—the middle of the night–I realized you could just take half of your body height to your chin and it seems to work out fine for most folks. It comes out to be one half of five-sixths your height (or five-twelfths your full height). For example, a six foot tall person is five feet to under the chin; and one half of five feet is two and a half feet or thirty inches. (Also 5/12 X 72 = 30).Which is the most typical dining table height and too high for most woman and children. Guess who made up the standards?