TV Size Calculator: Screen Size for Your Viewing Distance

Measure from where your eyes will be on the sofa to the wall the TV will hang on, and this calculator gives you a screen size range, the physical width and height of each size so you can check it against a chimney breast or alcove, and the height to mount it. The two figures most guides use come from the same geometry: the SMPTE guideline puts the screen at about 30 degrees of your view (sit roughly 1.6 times the diagonal away), and THX recommends about 40 degrees for a more cinematic feel (roughly 1.2 times the diagonal).

How the calculation works

A TV screen is a 16:9 rectangle, so its width is about 0.872 times the diagonal and its height about 0.490 times the diagonal. The angle the screen fills in your view depends only on its width and your distance: width equals 2 times distance times the tangent of half the angle. Rearranged for a 30 degree view, the diagonal comes out at about 0.61 times your distance; for 40 degrees, about 0.84 times. That is where the familiar "sit 1.6 times the diagonal away" and "1.2 times" rules come from.

Worked example: a sofa 2.8 m (about 110 inches) from the wall. At 30 degrees, 110 times 0.615 gives a 68 inch screen; at 40 degrees, 110 times 0.835 gives 92 inches. So a 65 inch set falls just under the comfortable end of that range (about 29 degrees), and 75 to 85 inches sits towards the immersive end.

Mounting height

For everyday watching, the centre of the screen should be close to your seated eye level, or a little below it, so you look straight ahead or slightly down. The calculator places the centre at your eye height and gives you the bottom and top edges. Above a fireplace the screen has to start above the mantel, which pushes it higher; the result tells you how far above eye level the centre ends up, so you can judge whether a tilting bracket or a different wall makes more sense.

Tips before you buy

• Mark the screen's width and height on the wall with painter's tape and live with it for a day. It is the quickest way to tell whether a size feels right in your room.
• Check the stand width too if the TV will sit on a media unit. Feet are often set near the edges, so the unit needs to be wider than the screen's footprint.
• With 4K sets you can sit closer than older guidance suggests before you notice pixels, which is why the THX end of the range has become more popular.
• For wall mounting, find the cables and pipes first and use fixings rated for the TV and bracket weight on your wall type.