King size mattress frame dimensions
A king mattress is 76 × 80 in. The frame around it is larger, and that's the size to measure the room for.
Short answer: a king size mattress is 76 × 80 in.[1 · Oct 29, 2026] One maker's frame chart lists typical king frames at about 78 to 82 in wide and 82 to 85 in long on the outside.2 A frame usually adds about 2 to 5 in on each side.2 Use the listed outside size of the frame you're buying.
King mattress and frame sizes
| Inches | Centimeters | |
|---|---|---|
| King mattress | 76 × 80 in[1 · Oct 29, 2026] | 193 × 203 cm |
| Typical king frame, outside | 78–82 × 82–85 in2 | 198–208 × 208–216 cm |
Ranges from one maker's frame size chart.2 Frames vary, so check the listing.
Foundation, headboard and room
- A platform or slatted frame supports the mattress on its own; a traditional metal frame needs a foundation.3
- Some king foundations come in two pieces, which makes delivery and setup easier.4
- One maker's minimum room for a king is 12′ × 12′.3 See will a king fit in a 12×12 room and the full bed frame size chart.
Questions people ask
What size is a king bed frame?
A king mattress is 76 × 80 in. One maker lists typical king frames at about 78 to 82 in wide and 82 to 85 in long on the outside. A frame usually adds about 2 to 5 in on each side.
Does a king size mattress come with a frame?
Not usually. The mattress and the frame are sold separately. Match the frame to a 76 × 80 in king mattress, then check the listed outside dimensions before you buy.
How much bigger is a king frame than a king mattress?
One maker says a frame usually adds about 2 to 5 in on each side. Its chart puts typical king frames at 78 to 82 × 82 to 85 in, versus the 76 × 80 in mattress.
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Sources: 1. Sleep Foundation, Mattress sizes and dimensions guide. 2. 
Casper, Bed frame size chart and dimensions guide. 3. Casper, Queen size bed dimensions: size, room fit, and how it compares. 4. 
Saatva help, What are the dimensions of the Saatva foundation?. Checked Oct 29, 2026. Trademarks belong to their owners; figures are restated in our own words and tables, not reproduced.