A² + B² = C²      C = sqrt(A²+B²)

4:3 Aspect Ratio

Width = 1.33 x Height

Height = .75 x Width

Diagonal = 1.25 x Width

16:9 Aspect Ratio

Width = 1.77 x Height

Height = .562 x Width

Diagonal = 1.15 x Width

5:4 Aspect Ratio

Width = 1.25 x Height

Height = .2 x Width

Diagonal = 1.28 x Width

1.85:1 Widescreen Letterbox

Height = .4762 x Diagonal

Width = .881 x Diagnal

Diagonal = H x 2.1

Diagonal = W x 1.135

2.35:1 CinemaScope

Height = .3915 x Diagonal

Width = .92 x Diagonal

Diagonal = 2.554 x Height

Diagonal = 1.0868 x Width

Image Size = Distance / Throw Ratio  20ft/1.5 = 13.3ft Image Size

Note: Because of Variations in Mfg Specifications this will either yield a Width or Diagonal dimension

Throw Ratio (These are approximations when in question use Mfg. Data)

Distance / Image Width

Based on Lens and LCD/DLP Panel Size = (Focal Length/ Panel Diagonal) x 1.15 or 1.25

16:9 screen use 1.15

4:3 screen use 1.25

Area of a Rectangle or Square

Length x Width

Brightness

cd/m^{2 =} Foot-lamberts x 3.43

Screen Brightness

Lumens / Screen Area in ft²