How to measure your window in three minutes

Measure the clear glass width at the height you want the perch to sit — not the frame width. Suction cups need to land on flat glass, at least 1 inch clear of any frame, seal or bead.

Then measure the depth of the sill below. If the sill projects more than 3 inches, choose a platform that mounts above it rather than resting against it.

Finally, run a fingertip across the glass. Textured, frosted, filmed or laminated safety glass with a surface coating will not hold a suction cup reliably. On those windows, a freestanding tower is the safer choice.