Display Calculators
TV size from viewing distance.
Enter how far your seat is from the screen to see the TV diagonal that fills a 30 degree or 40 degree view, and the 28 degree lower bound. This is the inverse of the TV viewing distance calculator. Runs in your browser; nothing is sent or stored.
Inputs
Result
Fill the form and press Calculate.
Worked example
Sitting 10 ft (120 in) from a 16:9 screen: a 30 degree view needs a width of 2 x 120 x tan 15 degrees = 64.3 in, which is a diagonal of 73.8 in. A 40 degree view needs a width of 2 x 120 x tan 20 degrees = 87.4 in, a diagonal of 100.2 in. A 28 degree view is a diagonal of 68.7 in (width 59.8 in).
How it works
Screen width = 2 x distance x tan(angle / 2); the diagonal follows from the aspect ratio (for 16:9 the diagonal is about 1.147 times the width). The angles come from the Optimum HDTV viewing distance - Wikipedia article: a 30 degree view is widely quoted as the SMPTE figure (though it reports no direct SMPTE recommendation), THX recommends about 40 degrees, and its range ends near 28 degrees.
These are seating guides, not requirements. Pick the nearest real size that suits your room and budget.
Sources: Optimum HDTV viewing distance - Wikipedia. Each opened 2026-10-08.
Planning guide only, not professional advice. Figures are estimates from the inputs you enter.
FAQ
What size TV should I get for 10 feet?
For a 16:9 TV, a 30 degree view at 10 ft (120 in) is a 73.8 inch diagonal, and a 40 degree view is 100.2 inches.
How do you work out TV size from distance?
Width = 2 x distance x tan(angle / 2). Then the diagonal = width x sqrt(16^2 + 9^2) / 16 for a 16:9 screen.
Is bigger always better?
Not necessarily. Geometry only says what fills a given angle. The 40 degree figure is the THX immersive guide, not a requirement, and room size and budget set the practical limit.
Which angle should I use?
Use 30 degrees for a more relaxed view and 40 degrees for a more immersive one. Both are widely cited guides, not mandatory standards.