Seating is the part of a dining table that is easy to get wrong in a shop. The label says "seats six", the photo shows six chairs, and then at home the elbows collide. The reason is simple: people need a certain stretch of table edge each, and the shape of the table decides how much edge you actually get.
Pick a shape, enter your table's size and choose how much edge each person gets. The plan shows where the chairs go, how many fit, and how much floor the whole set needs once chairs are pulled out. Try 120 cm round against 160 × 80 cm rectangular to see how differently they behave.
Most guides agree on about 60 cm of table edge for each person as a minimum, and around 70 cm if you like space for big plates or elbows. That is the whole idea. A table's length, or its circumference if it is round, divided by that figure gives the number of people who can sit without bumping.
The width of the table matters too. Plan on at least 40 cm of depth per place setting, so a table that is 80 cm deep works for two people facing each other, with a little room left in the middle for dishes. Much narrower, and plates start to meet.
A round table has no corners, so everyone sits at an equal distance and conversation is easy. It also wastes no length: a 120 cm round table seats about four to five, according to common guidance, and a larger one around 160 cm seats seven or eight. The catch is the floor. A round table is as wide as it is long, so a big one can be hard to fit in a narrow room, and it is awkward to push against a wall.
A rectangular table seats people along its two long sides, and the ends are a bonus. A 160 × 80 cm table seats six with a chair at each end, or four if you leave the ends free. It slides against a wall for everyday use, which helps in a small room or a rental. The corners can be a bit annoying for knees, so chairs near them need a little more room.
Whichever shape you choose, count the legs and the base as well. A table with legs at the corners or a single central pedestal leaves more of the edge usable than one with legs set inward.
You do not need a bigger table for a bigger crowd. A drop-leaf or extending table can be small day to day and open up when guests come. A second-hand table is a good way to try a shape before you commit; markets and local listings often have solid wooden ones at a fraction of the new price. If you already own a table, borrow two stools or a bench for the occasional extra guest. A bench can tuck under the table and give two or three people a place with less floor than separate chairs.
Renting and unsure? Try a taped outline on the floor at the table's real size, put your chairs round it and walk behind them. It takes ten minutes and shows you what the planner above cannot: your own room.
These are guidelines, not laws. If your family likes to sit close, a tighter edge is fine; if you love long dinners, go for the roomy end.