Label the physical span
For a shelf purchase, write “Clear space between the uprights: 72 cm” rather than “Shelf: 72.” If the seller lists inches, retain the seller’s original figure beside any conversion. Measure again before ordering when a small difference would make the item unusable. Name whether the figure describes available clearance, the product itself or the outer packaging. Those numbers answer different questions even if they are all printed in the same unit.
Work a conversion without losing the original
A listed width of 28 inches converts to 71.12 cm at 2.54 cm per inch. Against an opening measured at about 72 cm, that leaves less than a centimeter before allowing for uncertainty or clearance. Record the original 28 inches and approximate opening. Extra decimal places in the conversion do not make the opening measurement more precise.
Check the other binding constraints
Look at height, depth, door swing and any clearance the manufacturer specifies. A shelf can fit the opening across the front and still fail to pass a hinge. If a measurement decides an expensive purchase, ask the seller to confirm what their dimension includes.