Most living rooms get the TV first and the sofa second, so the sofa ends up wherever it fits. The distance matters more than people expect. Sit too close and your eyes keep darting across the screen. Sit too far and a big screen shrinks into a small picture. A good spot comes from one idea: how much of your view the screen fills.
Home cinema bodies describe a comfortable screen by its viewing angle: the width of your view that the screen covers, measured from your eyes. The usual guidance is around 30° (the SMPTE figure) as a calm minimum, and about 40° (the THX figure) for a fully immersive picture. Between them is a friendly zone for films and everyday TV.
For a standard widescreen (16:9) TV that turns into a rule of thumb you can use with a tape measure. A 30° view puts you at roughly 1.6 times the screen's diagonal away, and a 40° view at roughly 1.2 times. A 55-inch TV (about 140 cm across the corner) is comfortable from roughly 1.7 to 2.3 metres.
A bigger TV in the same room does not fix a far sofa; it just moves the comfortable range further away. The better question is how far back you can sit, then pick a size to match.
It also works the other way. If your sofa is already against the opposite wall and the distance is long, a large screen is what makes the picture feel right. If the room is small and the sofa is close, a mid-size screen is kinder to your eyes and your wall.
Distance is only half of it. Try to get the middle of the screen roughly at the height of your eyes when you sit. On most sofas that is somewhere around 100 cm from the floor, but sit down and measure yours. A TV mounted high over a fireplace is the classic cause of a sore neck.
Seats off to the side see the screen at an angle, and the picture gets dimmer and less accurate on many TVs. If the sofa has to sit to one side, angle it slightly towards the screen, or turn the TV on a movable mount.
Often the cheapest improvement is rearranging, not replacing. Try the sofa in two or three positions for a few evenings before you decide.
Tall or top-heavy TV units can tip, especially with children or pets in the home, so fix them to the wall with the anchors that fit your wall type. For wall mounts, follow the maker's instructions and use fittings rated for the TV's weight. If the wall has pipes or cables inside, get a professional to check before drilling.
A cosy room is not the one with the biggest screen. A calm sofa spot, a warm lamp beside it and a TV you can watch without craning are what make the evening feel good.
Probably nothing. Start by moving the sofa and measuring. Buy only once you know the distance and the width you have, and keep the viewing angle in mind: 30° to 40° is a good target.