Projector throw and screen size calculator

How the projector throw calculator works

The screen comes from your seating distance and the projector from the distance between its lens and the screen. For the screen the rule is the same as for TVs: the image width should fill at least 30° of your field of view (the SMPTE recommendation for mixed use, as RTINGS explains) and up to 40° for movies. The calculator finds the diagonals that give 30° and 40° in the format you pick (16:9, 2.35:1 or 4:3) and suggests the largest size on sale inside that range, since a projector is mostly for movies.

For the projector what matters is the throw ratio: lens to screen distance divided by the image width. With the projector 14 ft from a screen 104.6 in (8.7 ft) wide you need a throw ratio of 1.61. RTINGS groups projectors like this: ultra short throw below 0.4, short throw from 0.4 to 1, standard throw from 1 up. Above 2 we call it long throw: BenQ notes that most projectors traditionally sat around 2.

A worked example

In feet (US). The calculator opens with a 16:9 screen, the couch 12 ft away, the projector 14 ft from the screen and an 8 ft ceiling.

• At 12 ft the image width fills 30° with an 89 inch screen and 40° with a 120 inch one
• The largest size on sale in that range is the 120 inch screen: 104.6 × 58.8 in (8' 8 1/2" × 4' 10 3/4")
• Projector at 14 ft: 168 in ÷ 104.6 in = throw ratio 1.61, standard throw
• Look for a projector whose throw ratio range (its zoom) includes 1.61

In metres (UK and elsewhere). With the couch at 3.5 m the range is 85 to 115 inches, so a 100 inch screen (2.21 × 1.25 m); with the projector 4 m away the throw ratio is 1.81.

Screen size by seating distance and projector placement

16:9 screen, largest size between 30° and 40°:

Seating distance	Range	Screen
8 ft	59-80"	80"
10 ft	74-100"	100"
12 ft	89-120"	120"
14 ft	103-140"	135"
16 ft	118-160"	150"

Lens to screen distance for a 16:9 screen at a few throw ratios:

Throw ratio	100" screen	120" screen
0.25	1.8 ft	2.2 ft
0.5	3.6 ft	4.4 ft
0.8	5.8 ft	7.0 ft
1.2	8.7 ft	10.5 ft
1.5	10.9 ft	13.1 ft
2	14.5 ft	17.4 ft

Projector screen sizes: width and height

Screens are sold by diagonal; at the same diagonal the shape changes a lot with the format.

Screen	16:9	2.35:1	4:3
80"	69.7 × 39.2 in	73.6 × 31.3 in	64 × 48 in
100"	87.2 × 49.0 in	92.0 × 39.2 in	80 × 60 in
120"	104.6 × 58.8 in	110.4 × 47.0 in	96 × 72 in
135"	117.7 × 66.2 in	124.2 × 52.9 in	108 × 81 in
150"	130.7 × 73.5 in	138.0 × 58.7 in	120 × 90 in

The calculator skips sizes taller than the room and, when you pick the screen yourself, warns you if it does not fit.

Common mistakes

• Using the diagonal. Throw ratio is based on the image width, not the diagonal: work it out on the diagonal and the projector ends up too close.
• Measuring from the back of the projector. Measure from the lens to the screen; on a ceiling mount the body can stick out a good way.
• Reading one number on the spec sheet. Many projectors have a zoom and list a minimum and a maximum throw ratio: your value has to sit between them.
• Trusting a label between 1 and 1.2. Brands disagree there: RTINGS already calls it standard throw, Nebula only from 1.2. Go by the number, not the name.
• A slack screen with ultra short throw. The light hits the screen at a steep angle and RTINGS notes that flatness problems are easier to see.