Before you begin to install kitchen cabinets, you must measure and determine if your floors are level and walls are plumb. Marking reference lines to show you where to install the cabinets is the first and most crucial step in the installation process.
Check for level floors
Don't assume that your floor is level:
Lay a long 2 x 4 on edge against a wall where you will install the base cabinets and set a 4-foot level on it.
The long 2 x 4 spans a greater distance of the floor, giving you a more accurate reading with the level.
Lift one end or the board or the other as needed to center the bubble between the lines in the level's vial.
Use the level/straightedge to determine if there is any point higher along that wall or an adjacent wall where base cabinets are to be installed.
Place an end of the board on the first high point and extend the board further along the wall or to any adjacent walls, checking for level as you did in Step 2. To make sure that the highest point along the wall is not lower than a point 2 feet off the wall (rare), check with a 2-foot level perpendicular to the wall. If it is, you need to add the difference to the height of your reference line.
Mark the cabinet height
Measure up 34-1/2 inches from the highest point and mark the wall. Using a level, pencil a line on the wall to represent the top of the base cabinets.
Measure up 49-1/2 inches from the reference line at both ends and mark the wall to represent the top of tall cabinets and wall cabinets.
Measure up 19-1/2 inches from the reference line at both ends to represent the bottom of 30 inch wall cabinets.
When you have your measurements marked on the wall, have a helper assist you and snap chalk lines that represent the bottom and top of your wall cabinets. If you have shorter wall cabinets, such as those over a range or refrigerator, measure down from the top line a distance equal to the height of the cabinet to determine the bottom edge.
Locate the studs
Use a stud finder to locate each wall stud. In most construction, especially in homes built after the 1960s, the wall studs are spaced every 16 inches or 16-inches-on-center (16-o.c.). In older homes, spacing can vary. Mark each wall stud along the three level lines wherever cabinets will be installed.
After you've marked the wall stud locations, attach a temporary ledger board to help support the wall cabinets during installation. A 1-x-4 pine board works well. Secure the ledger board along and below the line that marks the bottom of your wall cabinets. Drive a 2-1/2-inch-long drywall screw into every other stud to secure the ledger board to the wall.
Determine whether walls are plumb
Place a 4-foot level vertically on adjacent walls at an inside corner. If the wall against which the cabinet end butts is out of plumb, you need to shim both base and wall cabinets as you install them to make them plumb. Cabinets that butt an out-of-plumb wall will leave a tapered gap you will need to address.
You must establish a plumb vertical reference line to locate the cabinet sides. Walls are rarely perfectly plumb. Starting at an inside corner, use a 4-foot level to check for plumb. If the top of a wall that the end of a cabinet butts into leans in, measure along the wall it will be installed on and mark a point that is equal to the width of the first cabinet. You can find this dimension on your cabinet order or by measuring the width at the front face of the cabinet. Then using your level, pencil a plumb line from that point to the floor. If the wall leans out, then measure out from the bottom of the wall to locate the reference line; and if it bows out at the middle, measure from the middle.