Fitted sheet test

The fitted sheet test is a quick way to check whether a crib sheet is the right size for the mattress it covers. A properly fitting sheet stays taut around all four corners with no loose fabric to pull up, bunch, or come untucked when the mattress is pressed down or a baby moves around on it.

This check matters more than it might seem, because mini crib sheets, standard crib sheets, bassinet sheets and pack 'n play sheets are all different sizes and are not interchangeable. A sheet that is even slightly too large for the mattress can bunch into folds, and one that is too small may pop off a corner, both of which create loose fabric near the baby's sleep surface.

To run the test yourself, pull the sheet fully over the mattress corners, then try to lift or pull the fabric away from the mattress edge. If it comes up easily or leaves visible slack, size down or try a different brand, since sizing can vary slightly between manufacturers even for the same stated mattress size. A common mistake is assuming a sheet labeled for a standard crib will work loosely on a mini crib mattress, when a properly sized mini crib sheet is the safer match.