by A king mattress measures 76 inches wide by 80 inches long (6 feet 4 inches x 6 feet 8 inches) — making it the widest standard bed size in the United States. If you are planning a master bedroom setup, comparing king to California king, or checking whether your room can handle the footprint, this page covers every dimension you need to make the right decision.
Our Top Pick in king: Saatva Classic
The Saatva Classic is our highest-rated innerspring hybrid — available in multiple firmness levels, free white-glove delivery, and a 365-night trial. It fits standard frames and is available in every size including king.
King Mattress Dimensions at a Glance
| Measurement | Inches | Feet | Centimeters |
|---|---|---|---|
| Width | 76" | 6'4" | 193 cm |
| Length | 80" | 6'8" | 203 cm |
| Typical thickness | 9–14" | — | 23–36 cm |
Minimum Room Size for a King Bed
A king bed requires significantly more floor space than a queen. Here is the breakdown:
- Absolute minimum: 12 x 12 feet — the bed fits but leaves limited clearance
- Comfortable: 12 x 14 feet — allows nightstands on both sides and foot clearance
- Ideal with full furniture: 13 x 14 feet or larger — adds space for a dresser without the room feeling cramped
The 76-inch width alone means the mattress spans 6 feet 4 inches. With a frame adding 2–3 inches per side, the total floor footprint reaches approximately 80–82 inches wide. If your bedroom is 10 or 11 feet wide, a king will feel uncomfortably tight — a queen is a better proportional fit. See our queen mattress dimensions page for the comparison.
King Bed Frame Specifications
King bed frames require more structural support than smaller sizes due to the wider span. Key dimensions:
- Interior (mattress area): approximately 77" x 81"
- Exterior width: 79–82" depending on rail design
- Exterior length: 83–87"
- Center support: Required — a center leg or mid-rail prevents sagging across the 76" span
When selecting a foundation, confirm it includes center support. A platform bed without a center beam will eventually bow under the weight of a king mattress. Our mattress foundation guide covers the best options for king-size setups.
King vs. California King: Which Is Right for You?
| Feature | Standard King | California King |
|---|---|---|
| Width | 76" | 72" |
| Length | 80" | 84" |
| Best for | Couples wanting width | Tall sleepers (6'2"+) |
| Sheet availability | Widely available | Harder to find |
| Frame availability | Standard sizing | Specialty sizing |
For most couples, the standard king wins on availability and per-person space. California king is the right call only if one or both sleepers are over 6 feet 2 inches and regularly find their feet hanging off the end of an 80-inch mattress. For the full comparison, see our California king vs. king guide.
King Mattress Size vs. Other Sizes
| Size | Width | Length | vs. King |
|---|---|---|---|
| Full | 54" | 75" | 22" narrower, 5" shorter |
| Queen | 60" | 80" | 16" narrower, same length |
| King | 76" | 80" | — |
| California King | 72" | 84" | 4" narrower, 4" longer |
| Split King | 76" (2x38") | 80" | Same overall, split in two |
A split king uses two twin XL mattresses side by side, creating the same 76x80 footprint as a standard king. This is the preferred setup for adjustable base users who want independent head and foot control. See our king vs. split king comparison for details.
Our Top Pick in king: Saatva Classic
The Saatva Classic is our highest-rated innerspring hybrid — available in multiple firmness levels, free white-glove delivery, and a 365-night trial. It fits standard frames and is available in every size including king.
Frequently Asked Questions
What are the exact dimensions of a king mattress?
A standard king mattress measures 76 inches wide by 80 inches long (193 cm x 203 cm). It is the widest standard mattress size sold in the US.
What is the minimum room size for a king bed?
The minimum recommended room size for a king bed is 12 x 12 feet. Most interior designers recommend 12 x 14 feet for comfortable clearance with nightstands and a dresser.
What is the difference between a king and a California king?
A standard king is 76 inches wide by 80 inches long. A California king is 72 inches wide by 84 inches long — 4 inches narrower but 4 inches longer. California king suits tall sleepers; king is better for couples wanting more side-to-side space.
What frame size do I need for a king mattress?
A king bed frame has interior dimensions of approximately 77x81 inches. Exterior dimensions typically reach 79-81 inches wide and 83-87 inches long. You will need a center support leg or rail to prevent mattress sagging.
Can I use queen sheets on a king mattress?
No. Queen sheets (60x80") are too small for a king mattress (76x80"). You need king-size sheets. The width difference is 16 inches — queen sheets will not stretch to cover a king.
Key Takeaways
- King Mattress Dimensions at a Glance: a key factor in making the right sleeping decision.
- Minimum Room Size for a King Bed: a key factor in making the right sleeping decision.
- It fits standard frames and is available in every size including king.
- With a frame adding 2–3 inches per side, the total floor footprint reaches approximately 80–82 inches wide.
- If your bedroom is 10 or 11 feet wide, a king will feel uncomfortably tight — a queen is a better proportional fit.
Our Top Pick: Saatva Classic
Voted best luxury innerspring mattress with exceptional lumbar support and white-glove delivery.
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