All projector lenses have a throw ratio. This is the ratio of the distance from the projector lens to the projection screen compared to the projection screen width. So, if you have a 2:1 throw ratio lens then for each 1 metre of screen with you'll need 2 metres of throw distance (don't forget to add the length of the projector itself when you are working out space requirements).
When you're looking at the our projector specification pages you'll find the throw ratio of the projector given under "Optical Features". If the projector can take various lenses then scroll down the specification page for a list of possible lenses.
We have a number of tools available to help you find a projector and lens based on your throw ratio requirements. Click Throw Calculator
for our tool that enable you to enter projector throw distance and projection screen size figures and see a list of matching projectors. On projector specification pages you can click on the graph shown under the key features (or the product description in the "Optional Lenses" table) to bring up the projector lens chart page, where you can enter and image width and see the throw distance and image brightness figures.