Find how far your projector must sit from the screen for the picture size you want, or the biggest image your room can fit. Enter the throw ratio from the spec sheet (including both ends of a zoom lens) and get the distance, image width and height, brightness needed and a good seating distance.
Last updated:
What do you know?
: 1
From the spec sheet. With a zoom lens, enter the short end (e.g. 1.36 of 1.36–2.18).
: 1
Leave blank for a fixed lens.
in
ft
Screen wall to the wall behind the projector.
ft
Projector depth plus cable and vent clearance.
Brightness check (optional)
Matte white is about 1.0; gray ambient-light screens 0.8–1.3.
lumens
ANSI lumens; calibrated output is often 30–50% lower.
Enter your values to see the result.
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How to use the Projector Throw Distance Calculator
Choose what you know: the screen size you want, or the depth of your room.
Enter the throw ratio from the projector specs; for a zoom lens also enter the long end.
Enter the screen diagonal in inches, or the room depth and how far the lens sits from the back wall.
Pick the aspect ratio of your screen.
Optionally add screen gain and projector lumens to check the picture will be bright enough.
Projector throw formulas
Image width = diagonal × w ÷ √(w² + h²) for an aspect ratio of w:h (16:9 → 0.8716, 16:10 → 0.8480, 4:3 → 0.8, 2.39:1 → 0.9225).
Throw distance = throw ratio × image width, measured from the lens to the screen.
Screen size from distance: width = distance ÷ throw ratio, then diagonal = width ÷ width factor.
Brightness: foot-lamberts = lumens × gain ÷ screen area (sq ft).
16:9 screen sizes and throw distances
Diagonal
Width × height
Throw 0.5:1
Throw 1.2:1
Throw 1.5:1
Throw 2.0:1
80 in
69.7 × 39.2 in
2 ft 11 in
7 ft 0 in
8 ft 9 in
11 ft 7 in
100 in
87.2 × 49.0 in
3 ft 8 in
8 ft 9 in
10 ft 11 in
14 ft 6 in
120 in
104.6 × 58.8 in
4 ft 4 in
10 ft 6 in
13 ft 1 in
17 ft 5 in
135 in
117.7 × 66.2 in
4 ft 11 in
11 ft 9 in
14 ft 9 in
19 ft 7 in
150 in
130.7 × 73.5 in
5 ft 5 in
13 ft 1 in
16 ft 4 in
21 ft 9 in
Placement tips
Check the projector's vertical offset spec too: it says how far above or below the lens the image appears, which sets the mounting height.
Prefer optical lens shift over digital keystone correction, which scales the image and softens it.
With a zoom lens, placing the projector near the wide (short) end usually gives a brighter picture.
Scope (2.35:1 or 2.39:1) screens need a wider image for the same height, so the projector sits farther back than for 16:9.
Frequently asked questions
How do I calculate projector throw distance?
Throw distance = throw ratio × image width. For a 16:9 screen the width is the diagonal × 0.8716, so a 120 in screen is 104.6 in wide; with a 1.5:1 projector the lens must be 1.5 × 104.6 = 156.9 in, about 13 ft 1 in, from the screen.
What is a projector's throw ratio?
The throw ratio is the distance from the lens to the screen divided by the width of the image. A 1.5:1 ratio means the projector must be 1.5 ft away for every foot of image width. Standard projectors are around 1.2–2.0, short throw about 0.4–1.0 and ultra short throw below 0.4.
How far should a projector be for a 100 inch screen?
A 100 in 16:9 screen is 87.2 in wide. At a 1.5 throw ratio the lens needs to be about 130.7 in (10 ft 11 in) away; at 1.2 about 8 ft 9 in; at 0.5 (short throw) about 3 ft 8 in.
How does a zoom lens change the distance?
A zoom lens has a range of throw ratios, such as 1.36–2.18. At the wide end the projector can sit closest for a given image; at the tele end it must be farthest away. Any distance between the two gives the same picture size by adjusting the zoom.
How many lumens do I need for my screen size?
Foot-lamberts = lumens × screen gain ÷ screen area in square feet. Home cinema guidelines aim for about 14–16 fL in a dark room, so a 120 in 16:9 screen (42.7 sq ft) with 1.0 gain needs about 680 calibrated lumens. Rooms with ambient light need two to three times more.
Is throw distance measured from the lens or the back of the projector?
From the front of the lens to the screen surface. When you plan a room, add the projector's body depth plus space for cables and ventilation behind it, which is what the lens offset input is for.
Where should I sit relative to a projector screen?
SMPTE recommends that the screen fill at least 30° of your view, which is about 1.87 × the image width; immersive setups use up to 40° (about 1.37 × width). For a 120 in 16:9 screen that is roughly 12 to 16 ft.
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