Microfiber Mops come in various sizes, from the very small 9" (with 10" pads) to the extremely long 48" (with 50" pads). Choosing the correct mop size for your needs depends on the cleaning task, and the size, shape and layout of of the space to be cleaned.
Generally, smaller mops (9") are used for cleaning tight spaces, with obstacles, like bathrooms; they can be used to scrub walls, bathtubs, and clean windows. The most common microfiber mop sizes are between 16" and 24". They are small enough to reach into tight spaces, but large enough to clean a sufficient area with one pass. They can be successfully used as dust mops and wet mops with the change of the pad.
The larger mops (36" through 60") are primarily used for cleaning large open spaces like gyms, halls, and hallways. The lend themselves to dust mopping because the larger mop sizes, when wet, can create too much friction and can be hard to push across the floor.
When buying mops online keep in mind that microfiber mop pads should always be larger than the hardware they attach to. Choosing the appropriate microfiber floor mop size will ensure that the edges of the hardware will not bang against walls and baseboards.