Split king bedding
Updated August 2026
A split king is not a size. It is a king footprint made of two twin XL mattresses, which means the bottom of the bed is bought in twos and the top of the bed is bought in ones — unless the base articulates, in which case that rule inverts too.
Exact dimensions
| Item | Dimensions | Notes |
|---|---|---|
| Each mattress (twin XL) | 38×80" | Buy fitted sheets in this size, two of them |
| Combined footprint | 76×80" | Identical to a standard king |
| King duvet cover / comforter | 104×92" | The single shared top layer |
| Two twin XL covers instead | 68×90" each | The two-duvet system for adjustable bases |
| Split-king flat sheet | Split from the head down | Sold specifically for articulating bases |
| Oversized cuts | 110×96" to 120×120" | For mattresses 14"+ on a tall base |
The one thing never to buy is a king fitted sheet. It spans both mattresses, ties them together and cancels the independent articulation you paid for. Twin XL sizing details are in twin XL bed covers, and the shared king dimensions are in king bed covers.
The drop math, worked out
Because two twin XLs make a 76×80" footprint, a shared king top layer behaves exactly like a king:
(104" cover − 76" combined mattress) ÷ 2 = 14" of drop per side.
| Mattress height | Drop per side | Hangs below the mattress | Result |
|---|---|---|---|
| 10" | 14" | 4" | Correct |
| 12" | 14" | 2" | Tight but tidy |
| 14" | 14" | 0" | Reaches the bottom edge and stops |
| 16" | 14" | −2" | Mattress visible below the hem |
The two-duvet alternative runs on different numbers. Each twin XL cover is 68" wide over a 38" half:
(68" cover − 38" half-mattress) ÷ 2 = 15" per side.
Centered on its own half, each duvet gives 15" of drop on the outside edge and pushes 15" toward the middle, where the two overlap by a combined 30". That mound in the center is the honest downside of the system. The fix is to slide each duvet outward by about 5", producing roughly 20" of outer drop and 20" of overlap — enough that no gap opens when one person turns, without a ridge down the middle of the bed.
Adjustable bases change the answer
If the base only ever lies flat, treat the bed as a king: one king cover, one king insert, a foam gap filler in the seam and a strap around both mattresses to stop them drifting apart. Everything above applies unchanged.
If the heads articulate independently, four things break:
- A shared king top layer drags. Raise one side 40 degrees and the cover is pulled off the flat sleeper. Two twin XL duvets solve it completely, and they solve mismatched sleeping temperatures at the same time.
- Flat sheets untuck. Every articulation pulls the tuck out at the foot. Either buy a split-king flat sheet designed for the base, or drop the flat sheet entirely and run the European system — the argument for and against is in do you need a top sheet.
- Bed skirts do not work. The base moves; a skirt gets caught in the mechanism. That removes the cheap fix for a shallow drop, so on a deep mattress you have to solve it with the cover itself — see oversized king bedding.
- Fabric near the hinge is a hazard. Keep the foot drop shorter than the clearance under the frame so nothing gets pulled into the pinch point when the base lowers.
Deep mattresses on a tall base
Adjustable bases add 14–15" of their own height under a 12–14" mattress, putting the sleeping surface roughly 26–29" off the floor. No standard-size top layer will ever reach the floor from there, so stop trying: the goal on a split king is a clean line at the bottom edge of the mattress, not a covered base. That makes a 14" drop adequate on a 12" mattress and inadequate at 14", where the choice is an oversized cut at 110" (17" per side, 3" hanging) or accepting the mattress edge as part of the look. The same reasoning applied to smaller beds is in queen bed covers, and all sizes are compared on the sizes hub.
What to buy for a split king
The shopping list is short and specific: two twin XL fitted sheets with at least a 14" pocket, one king top layer or two twin XL duvets, a gap filler, and pillow shams in king or standard depending on how much of the head end you want filled. Fabric-wise, a split king is usually a two-person bed with two thermostats, which is where a cooler-sleeping fabric earns its keep — linen at 160–190 GSM or percale at 110–140 GSM, rather than a heavy sateen.
- Best duvet covers — king cuts, plus the twin XL options for the two-duvet system.
- Best cooling comforters — for the sleeper who runs hot on the other half.
- Best comforters — king inserts by fill weight, 35–45 oz for all-season use.
Questions people actually ask
What size bedding do I buy for a split king?
Two twin XL fitted sheets for the mattresses and a single king top layer at 104×92". The bases are separate, the top layer is not. Never buy a king fitted sheet: it spans both mattresses and defeats the point of independent articulation.
Does a split king use the same top layer as a regular king?
Yes. Two twin XL mattresses at 38×80" each make a 76×80" footprint, which is exactly a standard king. A 104×92" king cover gives 14" of drop per side on both.
What works best on an adjustable base?
Two separate twin XL duvets rather than one king. When only one side elevates, a shared king top layer drags off the flat sleeper. Two 68×90" duvets give 15" of outer drop each and overlap generously in the middle, and each person can move independently.
How do I stop the two mattresses from separating?
Use a foam gap filler in the seam and a strap or connector around both mattresses if the base is used flat. On an articulating base skip the strap, since it fights the hinge, and rely on the gap filler plus a mattress pad wide enough to bridge the seam only at the foot.