BenQ MH520H User Manual page 15

If your measured projection distance is 4.8 m (4800 mm), the closest match in the
"Projection distance (mm)" column is 4788 mm. Looking across this row shows that a 140''
(about 3.6 m) screen is required.
All measurements are approximate and may vary from the actual sizes.
BenQ recommends that if you intend to permanently install the projector, you should physically test the
projection size and distance using the actual projector in situ before you permanently install it, so as to make
allowance for this projector's optical characteristics. This will help you determine the exact mounting position
so that it best suits your installation location.
Positioning your projector 15