A coverage number is a starting point for planning. It is not a promise that every square foot of a room can be protected with no gaps. The shape of the job matters as much as its area.
Read the dimensions of one sheet
A rectangular sheet measuring 12 ft by 10 ft has a nominal flat area of 120 sq ft. Three sheets of that size total 360 sq ft before folds, overlaps or cuts. This is arithmetic, not an allowance for the way the sheets will be used.
Use one unit system for your calculation. If a pack gives rounded metric dimensions beside imperial dimensions, multiplying the rounded metres may not reproduce its square-foot label exactly.
Measure over furniture
For a table or sofa, measure the distance the sheet must travel: up one side, across the top and down the other side. Repeat in the second direction. A flexible tape or a length of string is useful for following the shape.
As a worked example, a rectangular item 2 m wide, 1 m deep and 0.8 m high needs approximately 3.6 m by 2.6 m to reach the floor on all four sides. That simplified calculation has no spare margin. Arms, protruding corners and the way you secure the cover can require more.
Count separate covering tasks
List the sofa, sideboard, table and any other surfaces individually. Decide whether each needs one sheet or more. Add a separate allowance for joins and awkward shapes instead of stretching one sheet to satisfy a total-area target.
Before buying, compare your measured spans with the pack dimensions. Before painting, lay the covers out and check the real fit. A few minutes spent checking the edges can reveal a gap that the area calculation could not.