Measure underneath the table
Measure from the floor to the underside of the table and any apron or rail, not just to the tabletop. Record the space between legs where the chairs need to tuck in. An armchair may appear to fit in a product photograph yet stop well short because its arms meet the table edge. Check the chair's widest point as well as the seat. Draw the table and proposed chairs roughly to scale before assuming that a listed seating capacity will suit your layout.
Try sitting as you would at dinner
When possible, test a chair at a table with similar dimensions. Sit back, bring your feet into a comfortable position and rest your arms as you normally would. Check whether the table allows an easy eating posture rather than forcing raised shoulders or a long reach. A thick seat pad changes the relationship, so include it in the test if you intend to use one. Different people may prefer different chairs; a mixed pair can be a practical household choice.
Test the room around the chairs
Mark the chair positions on the floor and pull an existing chair out as if someone were getting up. Check the route behind it, nearby drawers and any doorway. A compact-looking chair with splayed legs can catch passing feet even when its seat is narrow. Consider how the material will be cleaned and whether chair feet are suitable for your floor. Choose the number that fits daily use comfortably, then make a separate plan for occasional extra guests.
