I find, the most frequently asked question by new cruisers, goes something like this :

How do I measure my luggage ?  Do I measure it standing up, or laying down ?

Let me put forth a couple of analogies....  A 25' flagpole, is 25' feet, regardless whether it is laying on the ground, or standing erect.     If you, are, say, 6' tall, you don't suddenly become 6' long when you go to bed.   You are still, 6' tall.

So, when measuring your luggage, L( length ) is always the longest side.  W (width) is the measurement across the top, parallel to the handle. H ( height ), is usually the shortest side. Across the top, perpendicular to the handle.   It is also the total depth of your suitcase.

So, unless you purchased some sort of magical luggage that changes dimensions depending on its special relationship, allow me to restate :

Length ( L ) = the longest side of your luggage

Width. ( W ) = the side across the top, usually the second longest side, parallel to the handle.

Height. ( H )= usually the shortes side, measured across the top, perpendicular to the handle..  think of it also as the depth of your luggage.

 

there it is in a nutshell.