Two numbers decide whether a table runner looks right: length and width. Most people get the length approximately right and the width badly wrong.
Length: the overhang rule
A runner should extend six to twelve inches past each end of the table. So the runner you want is the length of your table plus twelve to twenty-four inches.
| Table length | Runner length |
|---|---|
| 4 ft (48 in) | 60 to 72 in |
| 5 ft (60 in) | 72 to 84 in |
| 6 ft (72 in) | 84 to 96 in |
| 7 ft (84 in) | 96 to 108 in |
| 8 ft (96 in) | 108 to 120 in |
There is one legitimate alternative, which is a runner that does not reach the ends at all and instead sits in the middle third of the table. It works well on a round table, and on any table where you are already using placemats and do not want two layers of fabric under every plate.
What never looks right is a runner that ends flush with the table edge, or an inch short of it. It reads as a mistake rather than a choice. Either overhang properly or stop well short.
Width: about a third
The runner should be roughly a third of the width of the table, and never more than half.
Most dining tables are 36 to 40 inches wide, which puts the right runner somewhere between 12 and 18 inches. Go wider than about 20 and it stops being a runner and starts being a tablecloth that failed to cover anything. Go narrower than 10 and it disappears entirely the moment you put a bowl in the middle of it.
If you seat people along the sides, width also decides whether the runner ends up under the plates. Anything over 16 inches on a 36 inch table will, so plan for that rather than discovering it at dinner.
Running it across instead of down
On a long farmhouse table, a good alternative is to run several short runners across the width of the table, one per pair of seats, so each acts as an oversized placemat. It breaks up a long table visually and it is more practical, because each section can come off and be washed on its own.
For this, you want the runner to overhang the sides of the table by four to six inches on each side.
Round tables
Two runners crossed at ninety degrees through the centre works, and looks better than it sounds. A single runner on a round table is awkward, because the overhang varies as the table curves away, and there is no orientation where it looks intentional.
If you only have one runner and a round table, the short centre-of-table approach is the better option.
Coffee tables and consoles
Same third-of-the-width rule for the width. For length, reduce the overhang to four to six inches, because the pieces are smaller and a long overhang on a console reads as untidy rather than generous.
Napkin sizes, while we are here
Since people usually buy these together, and since the labels are unreliable:
Dinner napkins, 20 x 20 or 22 x 22 inches.
Lunch napkins, 16 to 18 inches.
Cocktail napkins, 10 to 12 inches.
A great many sets sold as dinner napkins are 18 inches, which is a lunch napkin with ambition. Eighteen inches will not stay on a lap.
One honest note
My own runner is 18 by 70 inches, which is worth being specific about, because 70 inches is not right for every table.
On a four-foot table it gives you eleven inches of overhang at each end, which is exactly right. On a five-foot table it gives you five inches, slightly under the rule but perfectly good. On a six-foot table it will not span the length at all, and you would be using it as a centre-of-table runner instead, which is a fine look but not what most people picture.
At 18 inches wide it sits at the top of the recommended range, so on a narrow table it will run under the plates.
I would rather you measure first than return it.
