Under the lower two thirds
A bedroom rug goes under the lower two thirds of the bed, stopping just short of the nightstands, so your feet land on it on both sides. You want at least 18 inches of rug either side and past the foot, 24 if the room allows.
For a queen (60 × 80 in) that's at least 96 inches across: an 8 × 10 laid sideways. A 5 × 8 leaves 2 inches each side and looks like a bath mat.
Questions
What size rug for a living room?
Most living rooms with a standard 84 in sofa take an 8 × 10 ft (200 × 290 cm) rug with the front legs of the seating on it. With every leg on the rug, or a sofa over 90 in, go to 9 × 12. Leave 12 to 18 inches of floor between the rug and the walls.
How far should a rug go past the sofa?
At least 6 inches past each end, 12 if you can. A rug narrower than the sofa makes the room look smaller.
What size rug for a queen bed?
An 8 × 10 ft rug laid sideways under the lower two thirds of the bed, which gives about 18 to 24 inches of rug each side. For a king, a 9 × 12.
How big should a dining room rug be?
At least 24 inches past every edge of the table, so chairs stay on the rug when pulled out. A 40 × 72 in table needs at least 88 × 120 in: an 8 × 10 ft rug.
How much floor should show around a rug?
12 to 18 inches in most rooms, down to 8 in a small one. Less than that and the rug looks like wall-to-wall carpet that didn't fit.
What are standard rug sizes?
In the US: 3 × 5, 4 × 6, 5 × 8, 6 × 9, 8 × 10, 9 × 12, 10 × 14 and 12 × 15 ft. In Europe: 80 × 150, 120 × 170, 160 × 230, 200 × 290 (or 200 × 300), 240 × 340 and 300 × 400 cm.