Chairs and chair arms should be able to slide under your dining table with ease, but they also must have comfortable lap and leg room when guests are sitting in them. Most dining tables are about 30 inch high. Chair height is generally 18 inch (from the floor to the seat).
Rules of Thumb
Allow 12 inches between the seat of your chair and your tabletop.
Leave 7 inches between the chair arm and the bottom or apron of the table.
Dining Chair Width
The average dining chair width is 16-20 inches. If dining chairs are placed right next to each other with no space between them, people will bump elbows when eating. Because of that, add 6 inches to each chair's width to accommodate the spaces between them. You'll also want to make sure there is enough room behind your dining chairs for people to slide out easily.
Rules of Thumb
Provide each guest 24-30 inches at the dining table.
For rectangular tables, add an extra 12 inches at each end for those seated at the head and foot of the table.
Allow for at least 36 inches between the dining table and any walls or other furniture.
Measure your chairs at their widest point. Depending on the style of the chair, this can mean either the seat or the chair back.
Typical Seating Guide
For standard size chairs, use the below estimates to plan how many people can fit comfortably around typical dining tables:
A 72 inch long rectangular table will comfortably seat six.
A 96 inch long rectangular table will comfortably seat eight.
A 120 inch long rectangular table will comfortably seat ten.
A 36-48 inch round (diameter) table will comfortably seat four.
A 60 inch round (diameter) table will comfortably seat six.
A 72 inch round (diameter) table will comfortably seat eight.
Arms will usually add about 6 inches to the overall width of a single dining chair. If space is limited, you may opt for armless dining chairs or only use dining chairs with arms at the head and foot of the table to conserve space.