King size mattress dimensions
A king is 76 × 80 in, the widest standard size. Here's the size in cm and feet, who it fits, and how it compares with a California king.
Short answer: a king size mattress is 76 × 80 in (193 × 203 cm), or 6′ 4″ × 6′ 8″.[1 · Oct 29, 2026] It suits couples who want the most width, or who share with a child: 38 in each (our arithmetic).[1 · Oct 29, 2026] One maker's minimum room is 12′ × 12′.2
King size mattress dimensions
| Inches | Centimeters | Feet | |
|---|---|---|---|
| Width × length | 76 × 80 in[1 · Oct 29, 2026] | 193 × 203 cm | 6′ 4″ × 6′ 8″ |
| Surface area | 6,080 sq in[1 · Oct 29, 2026] | ||
| Width per person, two sleepers | 38 in (our arithmetic: 76 in split in two) | ||
Width and length are standardized; thickness is not, so it varies by model.[1 · Oct 29, 2026] One maker lists its kings at about 76 × 79½ in, give or take ½ in,3 so measure your frame if the fit is tight. We converted to centimeters at 2.54 cm per inch[4 · Oct 29, 2026] and rounded to the nearest cm.
Who a king size mattress suits
- Two adults who want the most width: 38 in each, 8 in more per person than a queen (our arithmetic).[1 · Oct 29, 2026]
- A couple who often share the bed with a child.[1 · Oct 29, 2026]
- Anyone who wants sheets and frames that are easy to find, compared with a California king.1,3
A California king is 72 × 84 in: 4 in narrower and 4 in longer, better for taller sleepers or a pet at the foot.[1 · Oct 29, 2026] Compare them on king vs California king. Two twin XL mattresses side by side also make a king's 76 × 80 in footprint (a split king); see split king mattress sizes.
Room size for a king
One maker suggests about 12′ × 12′ for a king, compared with 10′ × 10′ for a queen.2 A frame can add up to 5 in each way.2 Walkway math is on will a king fit in a 12×12 room; a king can also work in a 10′ × 12′ room if the headboard goes on the 12′ wall — see what size bed fits a 10×12 room. Typical king frames are about 78 to 82 × 82 to 85 in on the outside; see king bed frame size.
Questions people ask
What are the dimensions of a king size mattress?
A king size mattress is 76 × 80 in, which is 193 × 203 cm, or 6′ 4″ × 6′ 8″. Thickness is not standardized and varies by model. One maker lists some kings at about 76 × 79½ in.
What size room do I need for a king mattress?
One maker suggests about 12′ × 12′ for a king. A frame can add up to 5 in each way. A king can fit a slightly smaller room, but the side walkways may drop below the common 24 in guideline.
Is a king or a California king bigger?
Neither is simply bigger. A king is 4 in wider (76 × 80 in); a California king is 4 in longer (72 × 84 in). Their surface areas are almost the same.
How does a king compare with a queen?
A king is 16 in wider and the same 80 in length, so each of two sleepers gets 38 in instead of 30 in. A queen fits a smaller room.
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Sources: 1. Sleep Foundation, Mattress sizes and dimensions guide. 2. 
Casper, Queen size bed dimensions: size, room fit, and how it compares. 3. 
Serta, King size mattress dimensions. 4. NIST, SI units: length. Checked Oct 29, 2026. Trademarks belong to their owners; figures are restated in our own words and tables, not reproduced.