Where a 42 inch cabinet fits
Cabinet width is the main constraint when planning a run, because the boxes have to total the wall length without an awkward filler. A 42" unit is one of the standard increments, which makes it straightforward to combine with other widths to close out a run cleanly.
Available configurations
Depending on the box type, 42" is offered as wall, base, or tall. Base cabinets are 24" deep and 34.5" high; wall cabinets are 12" deep in 30", 36", and 42" heights.
Planning a run
Measure the full wall, subtract appliance openings, then combine standard widths to fill the remainder. Fillers close gaps under 3" — anything larger is usually better solved by changing one cabinet width.