Projector Calculator
Use our projector calculator to calculate the suggested viewing distance, screen size, aspect ratio, screen brightness, and throw distance.
Calculate Viewing Distance
Calculate Screen Size
Calculate Aspect Ratio
Calculate Screen Brightness
Calculate Projector Throw Distance
Recommended Viewing Distance:
THX ideal recommended distance (40° viewing angle)  
THX max recommended distance (36° viewing angle)  
THX max acceptable distance (26° viewing angle)  
SMPTE max recommended distance (30° viewing angle) 
Diagonal:  
Width:  
Height: 
Suggested Projector Brightness
Fully Dark Room:  lumens

Dimly Lit Room:  lumens

Moderately Light Room:  lumens

Very Bright Room:  lumens

On this page:
How to Calculate Screen Viewing Distance
The optimal viewing distance from a screen depends on the screen’s width. Various standards define the proper viewing angle for viewing content on a projection screen.
THX recommends a viewing angle of 26° to 40°, with a preferred angle of 36° to 40° if possible. The Society of Motion Picture and Television Engineers (SMPTE) recommends a viewing angle of 30°. We have found that 38° to 40° results in the most immersive experience.
Viewing Distance Formula:
The formula that works best for us to calculate the viewing distance for a given viewing angle is:
d = w / 2 × tan(180 – θ / 2)
The viewing distance d is equal to the screen width w divided by 2, times the tangent of 180 minus the viewing angle θ divided by 2.
Try our TV size and distance calculator to calculate the optimal viewing distance for a television.
How to Calculate Screen Size
You can calculate the size of a projector screen given the diagonal measurement using the aspect ratio and the Pythagorean theorem. Use the formulas below to calculate a screen’s width and height.
Screen Width Formula:
screen width = AR_{w} × diagonal / √(AR_{w}^{2} + AR_{h}^{2})
The screen width is equal to the aspect ratio width AR_{w} times the screen diagonal divided by the square root of the aspect ratio width AR_{w} squared plus the aspect ratio height AR_{h} squared.
Screen Height Formula:
screen height = AR_{h} × diagonal / √(AR_{w}^{2} + AR_{h}^{2})
We go into much more detail about calculating screen size on our screen size calculator. Don’t forget to account for the ideal screen height for the optimal viewing experience.
How to Calculate Aspect Ratio
It’s possible to calculate a screen’s aspect ratio given either the image’s resolution or the width and height. First, find the greatest common factor between the screen’s width in pixels or inches and the height in pixels or inches.
Then, divide each dimension by the greatest common factor to get each part of the aspect ratio. You can also use an aspect ratio calculator to solve the ratio.
How to Calculate Screen Brightness
A projector screen’s brightness is one of the most important factors in a good cinematic experience. The screen’s brightness is typically measured in footlamberts or candela per square meter.
The projector’s luminosity and the size of the screen both contribute to the overall brightness. Some screens also incorporate gain to increase the amount of light reflected to the viewers, increasing the brightness.
Screen Brightness Formula:
You can use the following formula to calculate the brightness of your screen:
ftL = lumens × gain / screen square feet
The brightness in footlamberts is equal to the projector lumens times the screen gain, divided by the area of the screen in square feet.
How Much Brightness Do You Need?
You might be wondering how many footlamberts you need for a good experience. SMPTE recommends at least 16 footlamberts for a dark cinema.
Use the following chart as a guide for choosing the right screen brightness for your room.
015 ftL  Very low brightness 
1626 ftL  OK for rooms with no ambient light 
2739 ftL  OK for rooms with some ambient light 
4059 ftL  OK for rooms with moderate ambient light 
60+ ftL  OK for rooms with a lot of ambient light 
How to Calculate Projector Throw Distance
A projector needs to be installed at a specified distance from the screen to allow the image to fill the screen correctly. The distance varies by the lens used in the projector and the screen’s size.
The minimum and maximum throw ratio should be documented for every projector and is needed to calculate the throw distance.
Throw Distance Formula:
Given the projector throw ratio and the screen’s width, the following formula will calculate the throw distance.
td = tr × w
The throw distance td is equal to the throw ratio tr times the screen width w.