Projector Throw & Screen Size.

Throw ratio is the throw distance divided by the image width, so a ratio of 2.0 means the projector sits 2 m back for every 1 m of image width. As a rough guide, a standard lens is around 1.2 to 2.0, a short-throw lens around 0.5 to 0.8, and a long-throw lens about 2.0 or more. Always check your specific projector's spec sheet, because most have a lens range rather than a single fixed number.

Multiply your target image width by the projector's throw ratio. For example, a 3 m wide image with a 2.0 throw ratio needs about 6 m of clear throw distance. Switch the calculator to "Distance from screen size" mode to work this out, then add clearance for seating, aisles and sight lines so heads do not block the bottom of the image.

Divide the throw distance by the throw ratio to get the image width, then the calculator applies your chosen aspect ratio to give the height and diagonal. For example, 6 m of throw at a 2.0 ratio gives a 3 m wide image. Use "Screen size from distance" mode when the mount point or bump-in position is already fixed and you need to know how big the picture will be.

Pick the one that matches the content you are showing: 16:9 suits video, films and most modern slideshows, 16:10 is common for laptop and computer output, and 4:3 is mainly for older presentations or legacy sources. The aspect ratio sets the height and diagonal for a given width, so matching it to the source avoids black bars or a cropped image. If you are unsure, 16:9 is the safest default for events.

A common rule of thumb is that the image height should be at least one sixth of the distance to the furthest viewer, so text and detail stay readable from the back row. As a starting point, allow roughly 1 m of image height for every 6 m of viewing distance. Set your target width in the calculator and check the height and diagonal it returns, then confirm the room is dark enough and the projector is bright enough to fill that screen.