You can use the Throw-to-Width ratio to determine the correct projector lens to select for your needs.

1. If your throw distance will never change, you can select a lens with a fixed Throw to Width Ratio.

Example:

Divide the throw distance, from the front of the projector lens to the screen in inches, by the width of the screen in inches.

Formula: Throw Distance / Screen Width = Throw : Width Ratio

Throw Distance = 10' (120 inches)
Screen Width = 8' (96 inches)
Throw:Width Ratio = 1.25 : 1

Therefore, you would look for a lens that has a throw-to-width ratio of 1.25:1, (10' ÷ 8'):1.

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2. If your screen width varies, select a lens that offers a Throw to Width range.

Example,

Minimum image width

Throw Distance = 10' (120 inches)
Minimum image width = 5' (60 inches)
Throw:Width Ratio = 2:1

Maximum image width

Throw Distance = 10' (120 inches)
Maximum image width = 6' 8" (80 inches)
Throw:Width Ratio = 1.5:1

Therefore, a projector with a lens that is 10' away from a screen and is capable of creating image sizes from 5' wide to 6' 8" wide, would have a throw-to-width ratio of 1.5-2 : 1, (10' ÷ 6' 8") to (10' ÷ 5'):1.

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3. If both your throw distance and image size vary, select a lens that offers a Throw to Width range that meets your criteria.

Example,

Throw Distance = 8' (96 inches)
Minimum image width = 5' (60 inches)
Throw:Width Ratio = 1.6:1

Throw Distance = 12' (144 inches)
Maximum image width = 8' (96 inches)
Throw:Width Ratio = 1.5:1

Therefore, if you criteria requires a throw distance from 8' to12' and an image size from 5' to 8', you would look for a lens that has a throw-to-width ratio from 1.5-1.6 : 1, (8' ÷ 5') to (12' ÷ 8'):1.