The Best Daybeds That Convert to a King

It is king width. It is not king length.

Two standard twin mattresses side by side come to 76 by 75 inches. A standard king is 76 by 80 inches. So you get the full width of a king and you are five inches short on length.

Five inches sounds trivial and it is the difference between a tall person’s feet being on the mattress and over the end. If that matters to you, the format you want is a split king — two twin XL mattresses — and almost none of these frames take a twin XL, because the frame length is built for a 75-inch mattress.

Check the frame length before you assume. The Costway extends to 79 inches long, which leaves no room for an 80-inch twin XL. The ONBRILL frame is 77.56 inches long, same problem. These are twin frames, and twin is 75 inches.

First criterion: does the trundle actually lift level?

This is the whole mechanism and it is the thing to verify before you look at anything else, because the words in these listings are used loosely.

A pop-up trundle rolls out and then rises on a linkage until its sleeping deck matches the daybed’s. Two mattresses, one level surface. This is what you are paying for.

A roll-out trundle rolls out and stays down. It is a second bed at a lower height, and it is excellent at that — see the best daybeds with a trundle — but it will never make one bed, and a listing that says “twin to king” over a roll-out mechanism is overstating it.

An extendable or expandable daybed is usually a pop-up by another name, but confirm it rather than assuming. The Costway is described as extendable and publishes an extended footprint of 79 by 78 inches, which is consistent with the two decks meeting.

The tell on a listing is a stated extended or open dimension that is roughly double the frame’s depth. If a listing only ever gives you one footprint, it is probably a roll-out.

Second criterion: capacity, and the spread here is enormous

This is the one daybed format explicitly sold to hold two adults simultaneously, which makes the published capacity more important here than anywhere else on this site. The range across four frames is wider than on any other page we have written.

Two hundred pounds, on a bed sold to sleep two people, is a figure worth sitting with. It is not a reason the frame is badly made — it is a limit the manufacturer has published, and publishing it is more than Deolme has done — but it does not match the use the product name implies, and we would not put two adults on it.

The ONBRILL at 880 lb is the outlier in the right direction, on thickened metal bars with ten support legs. If two adults are genuinely going to sleep on this, that is the frame on this page built for it.

Third criterion: the two mattresses have to match

This is the part that catches people after delivery, and almost nothing in the category mentions it.

The frame levels the two decks. It does not level the two mattresses. So if the daybed has an eight-inch mattress on it and you put a six-inch mattress in the trundle, you have a two-inch step down the middle of the bed — and you will feel it exactly where two people meet.

Buy both mattresses together, in the same model and the same depth. That is the single most useful sentence on this page.

Then check the frame’s ceiling. The Costway recommends 6 inches. The Dream Solutions frame caps at 8 inches. ONBRILL and Deolme publish no maximum at all, which is marked as unstated in their spec blocks rather than guessed — on a pop-up mechanism the trundle mattress also has to clear the underside of the daybed frame when stowed, so an unstated limit is a real gap.

Which depth to choose is covered in the best daybed mattresses. The short version for this format: match the pair, stay inside the frame’s stated limit, and check the twin capacity specifically, because twin is often rated lower than every other size of the same mattress.

What it costs you in floor

A pop-up trundle does not escape the geometry. The second bed still has to come out sideways before it can rise, so you need roughly a twin’s width of clear floor beside the daybed.

So a frame about 41 inches deep becomes roughly 78 to 80 inches deep in use, and with the 30-to-36-inch walkway we use across this site — from the ADA accessible-route minimum of 36 inches of clear width — you want about nine to ten feet of depth measured out from the wall while both beds are up.

The compensation is that it is only committed while people are asleep in it, and the rest of the time you have a daybed. That is a better bargain than a permanent king, which is 76 inches wide forever.

Measure before you order — the routine is in how to measure for a sleeper sofa, and it applies to every format on this site rather than just to sofas.

The storage you lose, and the storage some of them keep

On an ordinary trundle daybed, the trundle doubles as an enormous flat drawer when nobody is sleeping in it. A pop-up trundle still does that — but two of the frames here go further and add dedicated drawers underneath as well.

The ONBRILL puts two storage drawers under the trundle, on wheels, with latches to stop them rolling open. The Costway has two as well and is the only frame on this page that publishes their inner dimensions: 31.5 by 15.5 by 3 inches each. Three inches is shallow — that is sheets and flat items, not a winter duvet.

The Dream Solutions and Deolme frames have no drawers, and on those the stowed trundle is your storage.

If storage is the actual priority rather than the king conversion, the comparison is in the best daybeds with storage, which covers drawers against trundles against open clearance.

Who should not buy one of these

Anyone who needs a genuine king length. You are getting 75 inches, not 80. If the person sleeping there is over about 5 ft 10 in, their feet are over the end, and no frame on this page takes a twin XL to fix it.

Anyone putting two adults on a 200 lb frame. Read the capacity figure before the product name.

Anyone who needs it to look like a sofa. A 42-inch-tall metal daybed with a trundle under it is unambiguously a bed. With a firm full-length bolster it becomes sittable — see how to make a daybed more comfortable — and it still reads as a bed.

Anyone who wants the floor back during the day. These are 41 to 47 inches deep permanently. A wall bed is 23.5 inches deep closed and gives the floor back every morning, if your ceiling and your lease allow it: daybed vs Murphy bed.

And if the second bed only needs to be a second bed rather than half of a king, an ordinary roll-out trundle is cheaper, simpler and has less to go wrong.

What we would buy

If two adults are actually going to sleep on it: the ONBRILL. An 880 lb published capacity on thickened metal bars with ten legs is the only figure on this page that comfortably matches what the format is sold for, and the drawers are a genuine bonus. Its cost is depth — 46.85 inches stowed is five inches more than an ordinary daybed.

If you do not want to buy mattresses separately: the Dream Solutions USA package, which includes two firm innerspring mattresses and therefore solves the matching problem for you by default. Its 350 lb ceiling is the constraint, and the included mattresses are a guest-frequency surface rather than something to sleep on nightly.

If the room is tight: the Deolme at 71.6 by 41.4 inches is the most compact frame in this format. Go in knowing it publishes neither a capacity nor a mattress limit.

If you want the published extended footprint: the Costway is the only one that states it. We would not put two adults on a 200 lb frame, and the listing contradicts itself on whether the result is a king or a full, so confirm with the seller first.