How to Use the Projector and Screen Calculator: A Step by Step Guide
A field by field walkthrough of the projector and screen calculator: what to prepare first, how to fill in every input, and how to read throw distance, mounting height, brightness and seating.
Table of Contents
The projector calculator solves screen and projector geometry in either direction. Give it a screen diagonal and it returns the throw distance the lens needs. Give it the throw distance you actually have and it returns the largest image that lens can fill. It then works out the mounting height, checks the screen against the ceiling and the projector against the room depth, converts lumens into foot-lamberts against the ambient light, and places the seating rows.
This guide lists every field the projector calculator asks for, what to enter, and what each output number means, in the order the interface presents them. Open the projector and screen calculator in another tab and work through it as you read.
The formula
Everything in projection geometry hangs off the first ratio. Throw ratio is the throw distance divided by the image width, and it is the number on a lens specification sheet, so a 1.5:1 lens filling a 3 m wide image needs 4.5 m of throw. A zoom lens quotes a range, and that range becomes a mounting window rather than a single point. The second equation is the brightness the audience actually sees: lumens reaching the screen, multiplied by the screen gain, divided by the screen area in square feet, giving luminance in foot-lamberts. Screen size itself comes from the diagonal and the aspect ratio, where the diagonal of the aspect rectangle gives a scale factor and width and height follow.
Before you start
Three inputs are mandatory and everything else refines the answer.
An aspect ratio – What shape the image is. Five standard ratios are offered plus a custom pair.
A size or a distance, and a throw ratio – Either the screen diagonal you want, or the throw distance you have, plus the throw ratio of the lens. Two of those three define the third.
The lens specification, if you have one – A real throw ratio range from the datasheet beats the class preset every time, because "standard zoom" spans a wide band across manufacturers.
Room dimensions, lumens and the ambient light condition are all optional, and the checklist on screen tells you what each one unlocks. Add the ceiling height and room depth and you get pass or fail checks on the mounting position. Add lumens and the ambient condition and you get a brightness verdict and a screen surface recommendation.
Input fields
Every control the projector calculator asks for, grouped by the panel it sits in, and listed in the order you meet it on screen.
Getting started
Load example – Fills a worked case: a 120 inch 16:9 screen, a standard 1.5 to 1.8:1 zoom lens, 15 per cent offset, a 2600 lumen projector on a 1.1 gain screen, in a 7.5 by 5 m room with a 3 m ceiling. It populates the inputs only. You still press Generate result to get an answer.
m / ft toggle – Sets the working unit for room distances. Screen diagonals stay in inches and throw ratios are dimensionless, because that is how both are specified in every market.
EN / ID toggle – Switches the whole interface between English and Indonesian. On the ALTA Integra site this follows the page language automatically.
Solve for
Throw distance – You state the screen size and the calculator returns the distance the projector needs to sit at. This is the direction to use when the screen is fixed by the room or the brief.
Screen size – You state the throw distance available and the calculator returns the image that lens can fill there, widest and narrowest across the zoom range. Use this when the mounting position is fixed by structure or by an existing ceiling plate.
Screen
Aspect ratio – 16:9 for HD and UHD, 16:10 for WUXGA, 4:3 for classic, 2.35:1 for cinemascope, 1:1 for square, or a custom width and height pair.
Diagonal, in inches – The screen size, when solving for throw distance. Screens are sold by diagonal everywhere, which is why this field is not unit-switched.
Throw distance – The distance available, when solving for screen size. This one does follow the m / ft toggle.
Frame or border per side – Optional, in inches. It affects the overall screen size for wall-space planning, not the image.
Projector optics
Lens type preset – Fills a throw ratio range from the common lens classes: ultra-short throw at 0.25 to 0.38:1, short throw at 0.5 to 0.8, short zoom at 0.9 to 1.4, standard at 1.5 to 1.8, standard wide zoom at 1.4 to 2.2, and long throw at 2.5 to 4.0. Entering a ratio by hand switches the preset to custom.
Throw ratio min and max – The lens range. A prime lens has a single value; enter it in min and leave max empty or equal.
Offset, as a percentage of image height – Where the lens sits relative to the image centre. Zero puts the lens level with the centre of the screen, fifty puts it level with an edge. Manufacturers quote offset this way rather than as a distance, which is why the field is a percentage.
Vertical and horizontal lens shift – How far the optics can move the image without geometric distortion, again as a percentage. Shift is not the same as keystone correction: shift moves the whole image optically with no loss, keystone stretches pixels and should be avoided on an installed system.
Room
Screen bottom above finished floor – The height of the bottom edge of the image. Together with offset this is what fixes the lens height.
Ceiling height – Enables the mount clearance check and the screen top check.
Room depth – Enables the room fit check and the seating check.
Room width – Enables the seating spread check and a warning when the screen leaves too little wall either side.
Light
Projector output, in lumens – The figure from the datasheet. Use the calibrated output if you have it rather than the headline number, which is usually measured in a bright, colour-inaccurate mode.
Screen gain – 1.0 for a unity-gain matte white surface, higher for a gained or ALR screen. Gain is not free performance: it narrows the viewing cone.
Ambient light condition – Dark room for a dedicated theatre at 16 to 26 foot-lamberts, low ambient for a living room at night at 27 to 39, medium ambient with curtains drawn at 40 to 59, and high ambient for a bright daytime room at 60 and above. This sets the target band the brightness verdict is measured against.
Geometry views
3D, Side, Plan, Front – Four dimensioned drawings of the same configuration. Side is the one that settles mounting arguments, plan is the one that settles seating arguments.
Reading your result
Press Generate result and the panel fills in. Nothing appears before that, and the button tells you how many required fields are still missing.
Screen dimensions – Image width, height and diagonal, the overall size with the frame, and the image area. A 2.35:1 mask bar figure appears when the image is narrower than scope, which is what you need to size top and bottom masking.
Mounting and placement – Throw distance at both ends of the zoom, the lens height above the floor, the window vertical shift opens up, the horizontal shift available, and the screen top height. The mounting window is the useful figure: it is the range of positions that work, not a single point.
Brightness – The image brightness in foot-lamberts, the target band for the ambient condition chosen, and the lumens required to hit that target. The verdict distinguishes useful headroom from genuinely too bright, because a little margin covers lamp ageing and eco mode brings it back into band.
Seating and viewing – Three distances: the immersive front row at the THX 36 degree angle, the reference distance at the SMPTE 30 degree angle, and a practical back row. Seat the front row no closer than the first.
Screen recommendation – A surface class for the ambient condition, with the reasoning. It carries one trap worth knowing: standard ALR rejects light arriving from below, which is exactly where an ultra-short-throw projector sits, so pairing the two washes the image out. A lenticular UST ALR surface is the correct pairing, and the tool says so when it applies.
Checks – Pass or fail on room fit, ceiling clearance, screen height, brightness, seating and screen width, each with a sentence explaining the verdict. This is where design decisions surface: a configuration that fits the room and clears the ceiling but seats the front row past the room depth is telling you the image is too large for the space, not that the projector is wrong.
Email me this result – Sends every figure above to the address you identified with.
Common mistakes
Using the headline lumen figure. The number on the box is usually a bright, colour-shifted mode nobody watches content in. Calibrated output can be a third lower.
Treating lens shift as free image placement. Shift has a range and using all of it can soften the corners. Design to the middle of the window, not the edge.
Confusing shift with keystone. Keystone correction throws away pixels to square up a distorted image. On an installed system, move the projector instead.
Specifying an ALR screen for a UST projector. The two reject light from opposite directions. This is the most expensive mistake on the page and the tool warns about it explicitly.
Ignoring the seating check. A large image in a shallow room forces the front row inside the immersive limit, where the audience cannot take in the whole frame.
Forgetting the wall. A screen that nearly spans the room width leaves nowhere for loudspeakers, doors or acoustic treatment. The width check exists because this is discovered on site otherwise.
When the projector calculator is not enough
This is single-projector geometry with a simplified brightness model. Four things sit outside it.
Multi-projector work. Edge blending, stacking for brightness or redundancy, and warping onto a curved or irregular surface are all absent.
Real screen behaviour. The brightness model treats the screen as uniform with a single gain figure. It does not model hotspotting, off-axis falloff, the measured performance of a specific ALR product, or room surfaces bouncing light back onto the screen, which is what actually destroys contrast in a bright room.
Sightlines. Real verification needs seating tiers, eye heights and head clearance in section. A raked floor changes the answer completely.
The rest of the system. Source resolution and frame rate, cable lengths and extender budgets, control, and acoustic coordination between the screen wall and the loudspeakers behind it are all part of a real design.
Treat the output as early-design geometry and equipment sizing, and as the input to a full audiovisual design rather than a substitute for one. Projection and display design is part of ALTA Integra's audiovisual consultant practice; if you need multi-projector blending, ambient light rejection modelling, sightline verification or full system documentation, talk to the team.
FAQ
Why does the projector calculator keep screen diagonals in inches?
Because screens are sold by diagonal in inches in every market, including metric ones, so converting the field would make it harder to match a product rather than easier. Room distances do follow the m / ft toggle, and the result panel reports the image width and height in the working unit alongside the inch figures.
What is throw ratio and where do I find it?
Throw ratio is the throw distance divided by the image width, and it is printed on the lens or projector specification sheet, usually as a range for a zoom lens. A 1.5:1 lens needs 1.5 m of distance for every metre of image width. The lens presets in the calculator cover the common classes, but a datasheet figure is always better because the classes span a wide band.
How many foot-lamberts should I aim for?
It depends entirely on the room. A dark dedicated cinema wants roughly 16 to 26 foot-lamberts, which is the range the film industry works to. A living room at night wants more, a room with curtains drawn more again, and a bright daytime space a great deal more. Choose the ambient condition in the calculator and it reports the band and whether your configuration lands in it.
Can I use an ALR screen with an ultra-short-throw projector?
Not a standard one. Standard ambient light rejecting screens are designed to reject light arriving from below and accept light from the front, which is the opposite of a UST projector sitting on a low cabinet. A lenticular UST ALR surface is built for that geometry, and the calculator flags the pairing when the throw ratio indicates a UST lens in a lit room.
What is the difference between lens shift and keystone correction?
Lens shift moves the whole image optically, with no loss of resolution or geometry, within a range the lens allows. Keystone correction resamples the image digitally to square up a picture projected off-axis, which throws away pixels and softens the result. On an installed system, use shift and physical positioning; keep keystone for portable use.
Who provides audiovisual and projection consulting in Indonesia?
ALTA Integra provides audiovisual consulting across Indonesia, including projection and display design, multi-projector blending, ambient light rejection modelling, sightline verification, sound system design and full system documentation. The calculator is the early-design tool; the design package is the deliverable.