Calculators

Projector throw and screen size calculator

The screen is not a choice you make. It is what the room and the lens leave you.

By the Refined Space editorial desk · Updated September 6, 2026 · How we work

On this page (6 sections)

Projector throw and screen size calculator
Throw ratio and lens distance: where each comes from
156 in of throw, worked by hand
Where the seats go, and where the maths hands over
174 in: the room a 156 in throw really needs
No lens shift, no screen gain, no ambient light

Short answer

At 156 in (3.96 m) from the screen, a lens with a 1.2 to 1.6 throw ratio produces an image 97.5 to 130 in (248 to 330 cm) wide, which in 16:9 is a 112 to 149 in (284 to 378 cm) diagonal. The middle of that zoom range, about 131 in (333 cm), is where the lens is sharpest and the picture brightest. Both ends of the range are the same projector in the same room.

The numbers, at a glance

Worked example throw distance: 156 in (3.96 m)Lens face to screen surface
Throw ratio range: 1.2 to 1.6From the projector specification sheet
Image width at that distance: 97.5 to 130 in (248 to 330 cm)Distance divided by the throw ratio
Diagonal in 16:9: 112 to 149 in (284 to 378 cm)Width multiplied by 1.147
Middle of zoom recommendation: 131 in (333 cm) diagonalSharpest optics, most light
Screen height at that size: 64 in (163 cm)Width divided by 1.78
Bottom of screen above floor: 24 to 30 in (61 to 76 cm)Single row of seating
Room needed to the projector back: 174 in (4.42 m)Throw plus 18 in of body
Cable allowance behind the body: 6 in (15 cm)Before the wall or the rack

Projector throw and screen size calculator#

Works in both directions. Give the throw ratio and either the room length or the screen you want, and the calculator returns the other, plus the screen height, the mounting offset and the seating distance the image supports.

Throw ratio, minimum

Throw ratio, maximum

Lens to screen distance in

Aspect ratio

Enter your measurements above.

Throw ratio is printed on the projector's specification sheet as a range for zoom lenses. Distance is measured from the front of the lens to the screen surface.

Nothing you type leaves your browser: the maths runs on this page, and no values are stored or sent anywhere.

Throw ratio and lens distance: where each comes from#

The throw ratio is printed on the projector's specification sheet, and on any lens with a zoom it is a range: 1.2 to 1.6:1 is typical for a domestic long throw model. Enter both ends. If the lens is fixed, put the same number in both fields and it returns a single size.

The distance is measured from the front of the lens to the surface of the screen. Three near misses cost people an image size: measuring to the wall behind a framed screen, which adds the 2 to 3 in (5 to 8 cm) the surface stands proud of it; measuring to the ceiling mounting plate rather than the lens, which sits forward of it; and taking a recessed screen to the face of the joinery rather than the fabric.

Everything the panel returns is derived from those two numbers and the aspect ratio, in your browser, as you type. Nothing you enter is sent anywhere.

156 in of throw, worked by hand#

Throw ratio 1.2 to 1.6, distance 156 in (13 ft, 3.96 m), 16:9.

Widest image, at the short end of the zoom: 156 divided by 1.2 = 130 in (330 cm).
Smallest image, at the long end: 156 divided by 1.6 = 97.5 in (248 cm).
Heights: 130 divided by 1.778 = 73.1 in (186 cm), and 97.5 divided by 1.778 = 54.8 in (139 cm).
Diagonals: multiply each width by 1.147, which gives 149 in (378 cm) and 112 in (284 cm).
Middle of the range: the two widths average 113.75 in (289 cm), a 131 in (333 cm) diagonal, 64 in (163 cm) high.

Step four is the only geometry in the calculation. The diagonal factor is the square root of one plus the inverse square of the aspect ratio, and it is why a 100 in 16:9 screen and a 100 in 2.35:1 screen are not the same object.

Aspect ratio	As a decimal	Height is width divided by	Diagonal is width multiplied by
16:9	1.778	1.778	1.147
2.35:1	2.350	2.350	1.087
16:10	1.600	1.600	1.179
4:3	1.333	1.333	1.250

A 120 in diagonal is 105 in wide in 16:9 and 110 in wide in 2.35:1, but only 47 in high instead of 59 in. Screens are sold on the diagonal and rooms are limited by the width, which is why every figure on this page is worked from the width.

The throw dimension runs from the screen surface to the lens, not to the wall behind the projector.

The zoom range is a brightness decision disguised as a size decision

The calculator recommends the middle of the zoom range and gives one reason: lenses are sharpest and pass most light there. The stronger reason is arithmetic, and it is worth setting out because it is what turns a size question into a picture quality question.

Between the two ends of a 1.2 to 1.6 lens at a fixed distance, the image width changes by a third, from 97.5 to 130 in. Area changes by the square of that, from 5,343 to 9,503 square inches, which is 78 per cent more screen. Light output does not change at all: the same lumens are being spread over it. So the large image is only 56 per cent as bright as the small one, from the same projector, in the same room, on the same evening.

Put numbers on it. A 2,000 lumen projector on a unity gain screen delivers about 54 foot-lamberts on the 112 in diagonal and about 30 on the 149 in, against the 16 foot-lamberts commercial cinema is calibrated to. Add any ambient light, or a laser source that has dimmed with age, or high dynamic range material that wants three times the reference level in its highlights, and the difference decides whether the picture holds up. The screen size you can fill is not the screen size you should choose. Give up 15 per cent of the diagonal and you get back nearly 40 per cent of the light, and the room stops needing to be perfectly dark.

Where the seats go, and where the maths hands over#

The panel reports a seating band of one to 1.2 times the image width: 114 to 137 in (290 to 348 cm) for the 114 in wide middle option. Those are close positions. Run the angle arithmetic yourself and you can see where they sit, because the distance for a given horizontal viewing angle is the image width divided by twice the tangent of half the angle.

30 degrees, the SMPTE figure for cinema: 1.87 times the width, or 213 in (5.41 m).
36 degrees, the THX recommendation: 1.54 times the width, or 175 in (4.45 m).
45 degrees: 1.21 times the width, or 138 in (3.51 m).
53 degrees: 1.0 times the width, or 114 in (2.90 m).

Read the calculator's band as the front row, not the reference row, and place the row you actually watch from between about 1.5 and 1.9 times the image width. Where the angle targets came from is set out in screen size and viewing distance: SMPTE and THX, and the row spacing, riser heights and sightlines for more than one row are in theatre seating rows, risers and sightlines.

The other output that needs judgement is the screen height. The calculator gives 24 to 30 in (61 to 76 cm) from the floor to the bottom of the image for a single row, which puts the centre of a 64 in (163 cm) high image at 56 to 62 in (142 to 157 cm). That is above seated eye height and it is deliberate, because a screen this size is a room feature rather than a television. With two rows on a riser, the bottom edge has to rise with them.

174 in: the room a 156 in throw really needs#

Throw distance is not room length. The panel adds 18 in (46 cm) for the projector body and asks for another 6 in (15 cm) of cable behind it, so a 156 in throw needs 174 in (4.42 m) from the screen wall to the back of the chassis and about 180 in (4.57 m) to the wall.

Check that figure first, because it is the constraint most likely to be already fixed: it has to clear the back wall, rear shelving, the door swing and the seating. Room proportions and the minimum room length for a given screen are in home theatre room dimensions and proportions, and the throw geometry itself in projector throw distance and screen size.

Where this goes wrong

The order most people use is screen, then projector, then room. It is backwards, and it produces the two failures that cannot be fixed afterwards: a lens position that lands exactly where a seat or a ceiling joist is, and an image so wide that the front row is inside the minimum viewing distance.

Work in this order. Measure the room. Find every position the lens can physically occupy, given the joists, the ceiling height, the door and the back wall. Take the shortest and longest of those distances and run them both. Only then choose a screen from the sizes that come out, and check that the seating you want falls between about 1.5 and 1.9 times the image width. If it does not, the screen is the variable to change, because the room is not.

One more: order the screen before the projector and the image width is fixed, which fixes the lens position. Buy the projector first and the zoom gives a foot or more of freedom.

No lens shift, no screen gain, no ambient light#

It sizes an image from a distance and a ratio. Several things that decide whether a room works are outside it.

No vertical or horizontal lens shift, and no offset. A projector with no shift throws the image entirely above or below the lens axis, which changes the mounting height completely.
No keystone, tilt or off-centre position: every figure assumes the lens square to the screen.
No brightness calculation, screen gain or ambient light. Levels around the screen are in media room lighting levels.
No speakers, no acoustics and no rack. Channel positions relative to the screen are in speaker placement dimensions for 5.1 and Atmos.
Nothing about flat panels, where the geometry differs and the distances are shorter: see TV size, distance and mounting height and the TV size and viewing distance calculator.

For the rest of the set, see the calculators index.

Frequently asked questions#

How do I work out what size screen my projector will fill?

Divide the lens to screen distance by the throw ratio to get the image width, then divide the width by the aspect ratio to get the height. At 156 in (3.96 m) with a 1.2 throw the image is 130 in (330 cm) wide. Because a zoom lens has a range of throw ratios, the answer is always a band rather than a single number, and the calculator reports both ends of it.

What is a throw ratio?

The distance from the lens to the screen divided by the width of the image it makes there. A 1.2 throw ratio means the projector sits 1.2 times the image width away. Fixed lenses have one figure and zoom lenses have a range, printed on the specification sheet as something like 1.2 to 1.6:1. Short throw lenses drop below 1.0, and ultra short throw lenses sit around 0.25.

Where exactly is the throw distance measured from?

From the front of the lens to the surface of the screen, not to the frame, not to the wall behind the screen and not to the mounting plate on the ceiling. A recessed screen in a frame can put the surface 2 to 3 in (5 to 8 cm) in front of the wall, and on a ceiling mount the lens can sit some way forward of the plate. Both errors change the image size.

Can I use it the other way round, from screen size to distance?

Not directly. The calculator runs from distance to screen size. To go the other way, multiply the screen width by the throw ratio: a 100 in (254 cm) wide image on a 1.4 lens needs 140 in (356 cm). Then enter that distance to check the answer and pick up the seating and room figures that go with it.

How far back should the seats be from a projector screen?

The calculator returns a band of one to 1.2 times the image width, which for a 114 in (290 cm) wide image is 114 to 137 in (290 to 348 cm). Treat that as the front row. The published angle targets are wider apart than they sound: a 36 degree image subtends at 1.54 times the width and a 30 degree image at 1.87 times, so a reference row sits further back than the band suggests.

Does a 2.35:1 screen need a different projector?

Not a different projector, but a different way of driving it. A cinemascope image on a 16:9 imaging chip uses only the middle band of the panel unless you add an anamorphic lens or use the projector's zoom memory to spill the unused image above and below the screen. The calculator flags this when you pick 2.35:1, because the screen size it gives is achievable but the pixel count is not automatic.

Sources and standards referenced#

Recommended practice for home theatre video design CEDIAScreen size, viewing angle and seating distance in dedicated rooms
ANSI/AVIXA V202.01, Display Image Size for 2D Content in Audiovisual Systems AVIXAImage height to viewer distance ratios
SMPTE viewing angle guidance for cinema presentation Society of Motion Picture and Television EngineersThe 30 degree horizontal viewing angle and 16 foot-lambert reference white
THX home cinema certification guidance THX LtdThe 36 degree recommended horizontal viewing angle
Projector specification sheets Manufacturer product documentationThrow ratio ranges, zoom ranges and chassis depths

We cite published codes, industry planning guidelines and manufacturer specifications. Where a figure is our own recommendation rather than a published standard, the text says so. See how we measure.