Measure the usable opening
Record inside width, depth and height in one unit. Exclude rails, door hinges and other obstructions. Check the opening you must move the object through as well as the space where it will sit.
Include the whole silhouette
Measure base, ears, outstretched parts and accessories. For plush, measure the pose you intend to keep without assuming it can be compressed. One dimension from a product title cannot describe its full footprint.
Read the layout honestly
The calculator compares uniform rows in one orientation with uniform rows rotated 90 degrees. It does not mix rotations or prove the mathematically best packing. Height must fit, and spacing applies between items rather than around the outer border.
Test before committing
Use paper footprints for a quick physical check. Leave practical handling room beyond a tight mathematical fit. Check the display maker’s load and installation instructions separately; the calculation does not assess weight, anchoring or stability.