Home / Free tools / Projector Throw Distance and Screen Size Calculator
Free tool

Projector Throw Distance and Screen Size Calculator

Reviewed for 2026, updated September 8, 2026.

Estimates the screen width and height, the lens to screen throw distance and the horizontal viewing angle from your seat, for anyone planning where a projector and screen will sit in a home cinema room.

Your numbers

Results update as you type.

Your estimate

Image width...
Image height...
Lens to screen throw distance...
Horizontal viewing angle from that seat...

Estimates only. Assumptions are listed below, and you can change every input.

A projector, a screen and a row of seats only work together when the geometry is right. Choose the screen before checking the throw ratio and the projector ends up too close to the back wall; pick the seats before checking the image width and the front row feels like sitting in the first row of a multiplex. Most spec sheets give you a diagonal and a throw ratio, then leave you to do the trigonometry yourself.

This calculator converts a screen diagonal and aspect ratio into the real width and height of the picture, multiplies the width by the throw ratio you read from the projector spec sheet to get the lens to screen distance, and then works out the horizontal angle that picture fills from your chosen seating distance. It is pure geometry with no hidden benchmarks: the numbers you enter are the only inputs to the result.

How to use this tool

  1. Enter the diagonal and aspect ratio of the screen you are considering, using the visible image area rather than the outer frame.
  2. Copy the throw ratio from the projector spec sheet; if it lists a range, enter the value for the zoom position you expect to use.
  3. Add the distance from the screen to the seat that matters most, then read the image size, the required lens distance and the viewing angle that seat will experience.

What the math assumes

  • Screen width and height are derived from the diagonal and aspect ratio with plain geometry; no overscan, masking or frame border is added.
  • Throw distance is throw ratio multiplied by image width, measured from the lens to the screen surface, and assumes the projector is aligned squarely with no keystone correction.
  • The viewing angle is the horizontal angle the image fills from a seat centered on the screen; off axis seats see a slightly narrower angle.
  • Zoom lenses have a throw range rather than a single ratio; the result applies to the specific ratio you enter.
  • No recommendation threshold is baked in; compare the resulting angle with whichever cinema guideline you prefer.

Frequently asked questions

What is a projector throw ratio and where do I find it?

Throw ratio is the distance from the lens to the screen divided by the width of the image. Manufacturers publish it on the spec sheet, usually as a range for zoom lenses, and a lower number means the projector can sit closer to the screen.

Should I measure the throw distance from the front of the projector or from the lens?

From the lens. Most spec sheets define throw from the front of the lens to the screen surface, so add the depth of the projector body behind the lens when checking clearance to the back wall.

Does this calculator account for lens shift or keystone correction?

No. Lens shift moves the image up, down or sideways without changing the throw distance, so it does not affect the result. Keystone correction should be avoided in a dedicated cinema because it reduces sharpness.

Why does a cinemascope screen with the same diagonal give a wider image?

A 2.39:1 screen spreads the same diagonal across a much wider and shorter rectangle than 16:9, so its width grows while its height shrinks. That is why scope screens need a longer throw for the same diagonal.

Embed this calculator on your site

Free to embed. Please keep the attribution line under the frame; it links back to this page.

Link to this toolhttps://theatrvault.com/tools/projector-throw-distance/

Free for readers and publishers alike. If you cite the result in an article, a link to this page helps others find it.

More free tools from Theatrvault

  • Dedicated Cinema Room Budget Estimator: Builds a realistic total budget for a dedicated home cinema room from your room size, construction rate, equipment allowance, seating plan and integration fees, for homeowners scoping a project before talking to an installer.
  • Lamp vs Laser Projector Break-Even Calculator: Compares the total cost of a lamp based projector, including replacement lamps, against a laser projector over your ownership period and shows how many years it takes for the laser premium to pay for itself.

A Cinema Kept Behind Your Own Door

An expert guide to designing a true home cinema.

Read the complete guide