How this calculator works
Seating capacity is really a perimeter calculation. Each person needs a strip of table edge, about 60 cm wide for a comfortable meal. On a rectangular table people sit along all four sides, so divide the length by the space per person, round down, and do the same for the width, then double both and add. On a round table the seating runs around the circumference, so multiply the diameter by pi, divide by the space per person and round down. The rounding down matters because a partial strip of table edge cannot seat anyone.
Formula
rectangular seats = 2 x floor(length / space) + 2 x floor(width / space). round seats = floor(pi x diameter / space). tables needed = ceiling(guests / seats per table).
Worked example
A 180 by 90 cm table with 60 cm per person seats 2 x 3 + 2 x 1 = 8 people. A 150 cm round table seats floor(3.1416 x 150 / 60) = 7 people. For 20 guests at 8 per table you need three tables, with four spare seats.
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Frequently asked questions
How much table edge does one person need?
About 60 cm is the usual comfortable allowance for a place setting. Banquet tables are often specified at 60 cm per person, while a family kitchen table can work at 50 cm if the plates are not too large.
Should people sit at the ends of a rectangular table?
The formula assumes they do. If the table is against a wall, or you want an open end for serving, subtract the seats that would be on that side.
How many people fit at a round table by diameter?
Roughly three at 90 cm, four to five at 120 cm, six at 150 cm and eight at 180 cm with a 60 cm allowance. Banquet halls sometimes squeeze in one more by using a 55 cm spacing.
Does a tablecloth change the answer?
Only through the usable edge. A cloth that overhangs a lot gets in the way of knees, but the seating count is set by the table top under it.