The most common mistake when buying a table isn't the type of wood or the finish – it's the size. A table that's 20 cm too big overwhelms the room; one that's 20 cm too small has everyone squeezing up at every meal.
Start with the number of places
The basic rule: 60 cm of table length per person along the long side, plus the ends. In practice, that means 180 cm for 6 people, 220 cm for 8, 260 cm for 10 and 300 cm for 12. A width of 90–100 cm is comfortable; below 85 cm, plates and serving dishes start bumping into each other.
Leave room to walk past
All around the table you need at least 80 cm to the wall or the next piece of furniture, so that the chairs can be pushed back. 100 cm is comfortable; at 70 cm you'll be bumping into things everywhere. Measure the room and subtract the clearance twice – what's left is the maximum length of the table.
Proportion matters just as much
A 300 cm table in a room 3.5 m wide only works if the rest of the furniture is understated. If the same room also holds a bookcase and a sofa, go one size down. Conversely, in a large living space a small table looks lost.
If you're unsure, mark the outline on the floor with masking tape and live with it for two days. It's the cheapest test there is.