📐 Home Theater Room Size Calculator

Enter your screen width and planned viewing distance to see the minimum recommended room width and length.

Screen width (ft)

Planned viewing distance (ft)

How the minimum dimensions are worked out

Two planning rules of thumb, one for each dimension:

minimum room width  = screen width × 3
minimum room length = viewing distance + 4 ft

With the defaults, a 7.3 ft wide screen wants a room at least 21.9 ft wide, and a 10 ft viewing distance wants 14 ft of length. The width rule leaves roughly one screen width of clear wall on each side, which is where the left and right speakers go without being jammed into corners. The 4 ft of length is the depth in front of the screen wall plus a walkway behind the last seat.

Choosing the viewing distance you feed it

The tool takes distance as an input rather than deriving it, so the standard is your choice. The two in common use disagree by a lot:

Standard	Horizontal angle	Distance for a 7.3 ft screen
SMPTE	30°	13.6 ft
THX	40°	10.0 ft

Distance is screen width / (2 × tan(angle / 2)). The 10 ft default is the THX figure; feed the SMPTE 13.6 ft in instead and the room needs 17.6 ft of length rather than 14.

These are space-planning minimums, not acoustics. They say nothing about ceiling height or room modes - a room whose length, width and height are simple multiples of each other stacks its resonances, so avoid cubes and exact 2:1 shapes even when the floor area is generous.

Frequently asked questions

How big a room do I need for a 100 inch screen?

A 100 in 16:9 screen is 87 in wide, or 7.26 ft, so about 21.8 ft of width. At the THX 40° distance of 10 ft you need roughly 14 ft of length; at the SMPTE 30° distance of 13.5 ft, about 17.5 ft.

Why does the room need three times the screen width?

To keep the left and right speakers off the side walls and give off-centre seats a usable angle. A screen that fills the whole wall leaves the front soundstage nowhere to sit and puts side seats at a hard viewing angle.

Does this include room for a second row?

No. The length figure covers one seating position plus circulation. A second row on a riser adds roughly 5 to 6 ft, so add that to the answer yourself.