What size TV unit, and how high to mount the screen?

The number that decides a TV unit's width isn't the TV's diagonal — it's the screen's actual width, and the two are easy to confuse. A 65in TV, measured corner to corner on a 16:9 panel, is only about 144cm wide. The unit underneath wants to be at least that wide, ideally 5-20cm wider in total so the screen doesn't overhang the ends.

Height follows a simpler, size-independent rule: centre the screen 100-110cm from the floor, whether it's wall-mounted above the unit or sitting on top of it. Below is the width by common screen size, and eight of our own units measured against real TVs.

Rule one. Diagonal is a sales number; width is the one that fits furniture

TVs are sold and marketed by diagonal because it's one number that sounds bigger, but nothing about a room actually cares about the corner-to-corner measurement — the unit, the wall space, and the shelf all care about the screen's actual width and height. Converting first avoids buying a unit that's technically 'the right size on the box' and visibly too narrow in the room.

The conversion is fixed for any 16:9 screen: width is about 87% of the diagonal. A 55in TV is roughly 122cm wide, not 140cm — worth doing the sum before measuring the space rather than after.

Rule two. The unit wants to be wider than the screen, not equal to it

A unit exactly as wide as the screen looks accidentally matched rather than deliberately chosen — the usual guidance is 5-20cm wider in total, split roughly evenly either side, so the TV reads as sitting within the unit's width rather than balanced precisely on the edge of it.

Much more than 20cm wider and the relationship reverses — the unit starts to look like the main piece of furniture with the TV as an afterthought on top of it, which suits a piece bought for its own storage more than one bought specifically to hold the screen.

Rule three. A hundred to a hundred and ten centimetres, wall-mounted or not

The centre of the screen at 100-110cm from the floor puts it at eye level for someone seated on a typical sofa, and this doesn't change based on whether the TV sits on the unit or is mounted on the wall above it. What changes is the unit's own height: a taller unit pushes a TV sitting on top of it higher, so the unit height and the screen's own height need adding together before checking against the 100-110cm target.

A wall-mounted TV skips that arithmetic — the unit underneath becomes pure storage, mounted at whatever height suits the room, with the screen positioned independently at the correct eye level.

Eight of our units, measured against real TV sizes

Width is what to check against the table above; the unit's own height and storage are the rest of the decision.

The short version

Convert diagonal to actual width first — about 87% of the diagonal for any 16:9 screen. The unit wants to be that width plus 5-20cm, not equal to it. Centre the screen at 100-110cm from the floor regardless of whether it's wall-mounted or sat on the unit, adding the unit's own height where the TV sits on top of it.