Calculator + chartEnter your measurements below and it works the answer out.
A 9 × 12 ft rug is the size that goes under a king bed properly — an 8 × 10 works only if you start the rug below the nightstands. A king is 76 × 80 in, so covering it with 18 in showing on both sides needs a rug 112 in wide, and only a 9 × 12 has that.
| Placement | Rug | What shows | Room it needs |
|---|---|---|---|
| Under the whole bed | 9 × 12 ft | 18 in each side, 64 in past the foot | Needs a room about 11 × 14 ft |
| From below the nightstands | 8 × 10 ft | 18 in each side of the lower bed | Needs a room about 10 × 12 ft |
| Runners either side | Two 3 × 8 ft | Covers where you step out | Any room that fits the bed |
| Too small — do not | 5 × 8 or 6 × 9 | Disappears under the bed | Looks like a mistake at any size of room |
Sized to show at least 18 in of rug at each side and past the foot, and to leave at least 6 in of floor between the rug and every wall.
Three placements, and the room decides which you get. Under the whole bed, from below the nightstands, or runners either side. All three are proper answers; the largest is not automatically the right one.
The 18-inch rule. A rug under a bed exists so you step onto it, so it has to show at least 18 inches at each side and past the foot. That single number generates every size on this page: bed width + 36 in is the rug width you need.
Then the walls. Leave at least 6 inches of floor between the rug and every wall. Closer than that and the rug reads as fitted carpet, runs under the wardrobe, and catches the door.
When the two collide, go smaller and change the placement. A rug that satisfies the 18-inch rule but runs to the skirting is worse than a smaller rug placed from below the nightstands. The calculator tells you which dimension ran out.
A 9 × 12 ft rug for the whole bed. A king is 76 in wide, and showing 18 in of rug on each side needs 112 in — a 9 × 12 is 108 in, which is the closest stock size and the one everyone uses. An 8 × 10 is 96 in and will not clear both sides.
Not under the whole bed. It is big enough if you start the rug below the nightstands, which leaves the head of the bed on bare floor and is a normal, deliberate placement. Under the whole bed it leaves almost nothing showing at the sides.
Two runners either side, 3 × 8 ft each. If a 9 × 12 would run within six inches of the walls it reads as fitted carpet and catches the door, and at that point runners are the better answer rather than a compromise.
At least 18 inches on each side and past the foot. That is enough to step onto when you get out of bed, which is the whole point of the rug — below about 12 inches it stops doing the job.
Either works. Under them looks more finished and needs the larger rug; starting the rug just below them uses a size smaller and is the usual compromise in a normal bedroom.
Also a 9 × 12. A Cal King is narrower than a standard king at 72 in but four inches longer at 84, so the width is easier and the length is tighter — a 9 × 12 handles both.