Projector Calculator

Use our projector calculator to calculate the suggested viewing distance, screen size, aspect ratio, screen brightness, and throw distance.

Select what you want to calculate:

Calculate Viewing Distance

Screen Size:

Calculate Screen Size

Enter One Screen Dimension:

Calculate Aspect Ratio

Aspect Ratio

Calculate Screen Brightness


Calculate Projector Throw Distance

Projector Throw Ratio
Screen Size

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)
Learn how we calculated this below

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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 = ARw × diagonal / √(ARw2 + ARh2)

The screen width is equal to the aspect ratio width ARw times the screen diagonal divided by the square root of the aspect ratio width ARw squared plus the aspect ratio height ARh squared.

Screen Height Formula:

screen height = ARh × diagonal / √(ARw2 + ARh2)

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 foot-lamberts 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:

ft-L = lumens × gain / screen square feet

The brightness in foot-lamberts 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 foot-lamberts you need for a good experience. SMPTE recommends at least 16 foot-lamberts for a dark cinema.

Use the following chart as a guide for choosing the right screen brightness for your room.

chart showing the optimal screen brightness for various types of rooms
0-15 ft-L Very low brightness
16-26 ft-L OK for rooms with no ambient light
27-39 ft-L OK for rooms with some ambient light
40-59 ft-L OK for rooms with moderate ambient light
60+ ft-L 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.