Seat height is usually 18"

I assume you mean the back of the chair, rather than the seat height (which would be pretty standard)?

We have a rustic wood table. We got tall rattan chairs, and ended up hating them (too big and bulky). So we were on a quest for new chairs. I can tell you this - there is no standard, and what looks good depends on the table and the room it's in. We ended up with chairs that are about 4-5" taller than the table, anything shorter "disappeared" and anything taller looked just looked wrongly proportioned. I think short chairs (the ones that are only as high as the tabletop) only look good with glass-top tables. Fortunately, we were able to bring home various "samples" before making our decision.

Thanks Annie. I should have said chair back height - is there a rule about proportion - how high a chair back should show above the table top?

sjhockeyfan, just saw your post. Yes, exactly, that's what I referring to. I am trying to help someone with DR chairs and thought maybe there was some rule of thumb I didn't know about regarding chair back height showing above the table. Thanks so much for sharing your findings!

Chair back heights are a matter of taste...you can go tall...

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[Contemporary Dining Room[(https://www.houzz.com/photos/contemporary-dining-room-ideas-phbr1-bp~t_722~s_2103) by Shawnee Interior Designers & Decorators Tran + Thomas Design Studio

or small

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[Contemporary Dining Room[(https://www.houzz.com/photos/contemporary-dining-room-ideas-phbr1-bp~t_722~s_2103) by New York Interior Designers & Decorators Mendelson Group

Thanks, Annie. Visuals are wonderful and very helpful!