What Is a Split King Bed?

Updated November 7, 2026 · By Serge, King Size Bed

A split king bed is a king bed made of two twin XL mattresses, each 38 x 80 inches, placed side by side on one king frame. Our twin XL dimensions guide has the details of that size. Together they cover 76 x 80 inches, the same as a standard king, so the frame, headboard and room size stay the same. What changes is that each side can have its own mattress and its own adjustable base.

Split king size: the measurements

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The guideline published by the International Sleep Products Association lists the twin XL at 38 x 79.5 inches and the king at 76 x 79.5 inches, with half an inch of tolerance either way. Our twin bed dimensions guide compares the twin and the twin XL. Two twin XL mattresses side by side therefore make exactly one king. Labels round the length to 80 inches.

The guideline has no split California king, but the mattress makers that sell one list each half at 36 x 84 inches, and one foundation maker sells it as two 36 x 84 inch pieces: a 72-inch-wide California king cut in two. Not sure which of the two kings you need? See our king vs California king guide.

Split king box spring and adjustable base sizes

A split king box spring is two twin XL box springs, one under each mattress. Each is made for a 38 x 80 inch mattress, so the pair covers 76 x 80 inches, the footprint of one king box spring. A split king adjustable base works the same way: two twin XL bases side by side, each raising its own half. For a split California king, the foundation maker quoted above sells two 36 x 84 inch pieces.

Split king vs king: what actually changes

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The frame column is the one people get wrong. A split king does not need a special frame: the two mattresses take the same 76 x 80 inch space as a king mattress, so any king frame holds them, as long as it supports the middle. That is the part of the frame most listings never describe. More on it below.

Why couples choose a split king

Two different mattresses. One side can be firm and the other soft, or one side can be memory foam and the other a hybrid. With one king mattress, you both sleep on the same one.

Two adjustable bases. This is where a split king makes the biggest difference. On a split king adjustable base, each twin XL half has its own motor, so one person can raise their head to read while the other stays flat. A single king adjustable base moves the whole surface at once.

Replacing one side. If one mattress wears out first, you replace a twin XL, not a king.

For a smaller room or budget, our full vs queen comparison shows each of two sleepers gets 27 inches on a full and 30 on a queen, against 38 on each half of a split king.

The downsides

The seam in the middle. Two mattresses leave a line down the center. One mattress maker says its edges are rounded, "therefore there may be a slight gap, but most owners do not feel it". Another suggests a topper or a bridge to fill it, but adds that this "is not recommended if you have a dual-control adjustable base", since a bridge would stop the two sides from moving on their own. If the two mattresses drift apart, the fixes for a sliding mattress apply to each half: see how to keep a mattress from sliding.

Cuddling. The same seam is where two people meet in the middle. A mattress maker lists this itself: the separate mattresses and the small gap between them "may make it difficult to cuddle".

Sheets. You need split king sheets or two twin XL fitted sheets, and making the bed takes longer.

Price. Two twin XL mattresses usually cost more than one king, and two bases cost more than one. Mattress makers put the higher price in their own list of drawbacks.

Does a split king fit a regular king bed frame?

Yes, if the frame supports the center. The two twin XL mattresses meet exactly over the middle of the frame, so the slats and the center rail carry the seam. Two mattress warranties we read spell out what that support has to be:

• one asks for a center support, at least 5 or 6 legs on a king frame, and slats "no more than 3.5 inches apart";
• another stays valid on a platform bed with "slats spaced less than 4" apart and a center support for queen and larger sizes".

Four other brands we checked publish no slat figure at all in their warranty pages. When the maker of your mattress does not say, use 3.5 inches as the limit. Our Tahoe low profile king bed frame, for example, has 12 slats 3 inches apart.

We then read the specifications of the 249 king bed frames listed by a US furniture distributor:

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So on these listings, roughly 7 frames in 10 that publish their slat spacing already meet both warranty limits, and 3 in 10 do not. More than half of the 249 frames do not publish the spacing at all. If a listing is silent, ask for it before you buy. With slats 4 inches or more apart, lay two twin XL bunkie boards (or one king-size board) on the slats. On a frame that needs a box spring, use two twin XL box springs, one under each mattress. Not sure your frame needs one? Our guide answers do you need a box spring frame by frame.

Everything else about the frame is the same as for a king. The outside size is what has to fit your room: across 545 king frames listed by US online stores, the median was 80 inches wide and 86 inches long. Our king size bed dimensions guide has the room sizes and a fit check.

Putting a split king adjustable base on your frame

Split king adjustable bases are made to work with an existing frame. One base maker says its bases "fit inside any standard-sized bed frame, on top of a platform bed, or directly on the floor". Another sells zero-clearance models that sit flat on top of an existing frame, with stackable 3-inch legs for more height.

Two things to check before ordering. First, the inside of the frame: the base has to drop between the side rails, or sit on a platform deck that is strong enough for it. Second, the height: the base adds its own thickness under the mattress, so check that the headboard still shows above the mattress once everything is stacked.

Split king sheets

A split king sheet set is two twin XL fitted sheets and one king flat sheet. Two mattress brands that sell these sets describe them the same way; one adds two king pillowcases; our king size pillow dimensions chart lists the pillowcase sizes too. Your king comforter, duvet and pillows all still fit, because the bed is still king size on top. Our king size bedding dimensions guide lists the sizes 19 US brands give for each piece.

You can also buy two twin XL fitted sheets separately. On a split adjustable base, each side needs its own fitted sheet so that it can rise on its own; a single king fitted sheet over both halves only makes sense if the bed always stays flat.

Sleeping on one California king mattress rather than a split pair? Our guide to king sheets on a California king goes through each piece of bedding, size by size.

Is a split king worth it?

Buy a split king if you want two adjustable bases, or if the two of you want mattresses that are really different. Those are the two jobs a standard king cannot do.

If you simply want the biggest standard bed for two people, and you like meeting in the middle, a one-piece king is simpler: one mattress, one set of sheets, no seam. The frame is the same either way, so you can switch later without replacing it. If you are still choosing a size, our king vs queen guide compares the two.

Shop king beds by style

Every bed in these collections lists its outside size on the product page, so you can check it against your room and your mattress before you order.

• All king bed frames
• By build: king platform beds, upholstered king beds, wood king bed frames, king beds with storage and king beds with drawers
• By height: low profile king beds, king floor beds with no gap underneath, king bed frames high off the ground with 10 to 14 inches underneath, and king beds with a tall headboard
• By look: modern, mid-century, rustic, cloud beds, velvet, black, brown, beige, gray, white and cream, wingback, boucle, linen, faux leather, solid wood, canopy, sleigh, rattan, metal, tufted, farmhouse and panel king beds, and king beds with a bookcase headboard
• For a 72 x 84 inch mattress: California king bed frames, including California king platform beds that need no box spring
• A few of our king beds: Burbank cloud bed with side shelves, Biloxi canopy bed, Montauk storage bed with 8 drawers and Fresno wood platform bed

Frame figures: specifications of 249 king bed frames listed in the catalog of a US furniture distributor, read on September 30, 2026, and listed outside dimensions of 545 king frames listed by US online furniture stores, read on September 29, 2026. Warranty and product quotes come from the published pages of the brands, read on September 30, 2026.

Not sure a split king is the right size at all? Our chart of mattress sizes lists every US bed from twin to California king in inches, next to the outside size of the frames.