The bed wall tends to get treated as the last thing to sort out. I notice it when people describe their spaces: they have made decisions about every other surface, and the wall above the headboard is still blank a year in. Often the trouble is that they are looking at the wall rather than at the bed. The bed is what sets the proportions here. Size to it, and the rest is mostly arithmetic.
The mechanics of that arithmetic, the two-thirds to three-quarters rule and how to work it, live in the wall art size guide. What follows is only the part a bedroom changes: which measurement to use, how high to set the work, what to know about finish and lamplight, and whether the wall is even the right place.
One piece, sized to the headboard
Over a bed I would almost always start with a single framed work. One piece, given room on either side, settles the wall more reliably than a cluster or a grid. The measurement to use is the headboard width, not the bed frame and not the bare wall. A queen headboard runs around 150 to 160cm; a king around 180 to 195cm. Take two-thirds to three-quarters of that as your target and hold the framed dimensions of a work against it. The framed piece is always larger than the bare sheet, so each work's own page lists those framed dimensions: those are the numbers to carry.
Over a queen that target usually lets a single framed work read as a composed choice with clear space on either side. Over a king, one piece can sit small, and that is where a wider answer earns its place.
When a wide bed wants more width
Over a wide bed, a cluster of three to six works hung as one block is the reliable alternative. Plan it as a single shape before anything touches the wall: lay the frames on the floor, keep an even gap of a few centimetres between them, and let the outer edges land on your target width. Once it is on the wall, the group should read as one object, not as individual frames that happen to be near each other. The gap from the bottom edge of the cluster to the top of the headboard should be the same even distance you would leave with a single piece.
Very large single works exist, but they are rare and are the exception rather than a practical plan.
The gap above the headboard
Above a bed the height rule is not the open-wall rule. Leave 15 to 25cm of clear wall between the bottom of the frame and the top of the headboard. That gap keeps the work and the bed reading as related rather than separate. Above a bed without a headboard, bring the work down a little so it still belongs to the sleeping space rather than drifting towards the ceiling. With a cluster, measure from the bottom edge of the whole group.
Finish and the bedside lamp
A bedroom changes one thing about finish. A flush mount sits behind plain glass, the most reflective of the framed options, and a bedside lamp that rakes across it in the evening can throw glare back at you in bed. Where a work offers a float or shadow box, those carry Artglass, which is anti-reflective and reduces that glare considerably. Not every work offers those finishes, so if the piece you want does not, the simpler fix is placement: set the work off the direct line of the lamp rather than square into it. Which finishes a work carries is listed on its own page; how each is built and glazed is in the guide to framing a fine art print.
A small object instead
The wall is not the only answer above a bed. A small object on a shelf or a picture ledge above the headboard can hold that space without anything fixed over a sleeping head, which some people prefer on grounds of weight and peace of mind. White Bird and the Solace figurine, both from the FIGURES collection, sit naturally this way. Either can rest on a low ledge near the bed, without needing a hook in the wall above where you sleep.
Before you hang it
Do the cheapest thing first. Cut paper to the framed sizes and tape the shapes to the wall over the bed. Then live with them for a day and an evening. The lamplight in the evening tells you things the daytime cannot: where the glare lands, how the gap above the headboard actually reads when you are lying down, whether the shape is too wide or still too narrow.