Setting electrical outlets and wall switches and standard, uniform heights is important both for ease of installation, and for the convenience of users.
Installing multiple boxes along a wall is much faster and easier when each box is the same height. Any variance in height slightly increases the friction on the NM (non-metallic) cable as you fish it through the holes drilled into the studs. Uniformity becomes even more critical when you are pulling rough-surfaced BX armored cable through studs. Uniform box heights also help with cutting and placing the insulation in the walls and attaching drywall to the studs.
Setting standard box heights is also important in terms of access and ergonomics. Irregular heights for light switch heights, for instance, can be disorienting. Boxes placed too high or too low can be inconvenient or even inaccessible to disabled or elderly residents.
Electrical Code and Box Heights
Although the National Electrical Code (NEC) has many very precise regulations for most aspects of residential wiring, it does not specify one height for standard wall outlets (receptacles) or for light switches. As a result, heights are often a matter of convention or preference. However, your local electrical code is the ultimate voice with these matters, since municipalities often adopt and adapt model building codes. Be sure to check with your city's building department for any specific requirements.
Although the NEC is silent regarding heights for box installations, electricians typically follow common professional standards, within a range generally considered acceptable. While it's best to stick to box height standards as much as possible, sometimes boxes may have to be slightly raised or lowered due to circumstances. For example, if you are finding it too difficult to drive a nail into a wood knot in one of the studs, it is permissible to move the box slightly up or down to avoid the knot.
Standard Height for Outlet Boxes
The standard height for wall outlet boxes is about 12 inches from the top of the floor covering to the bottom of the receptacle box (or 16 inches to the top of the box). If you are setting box heights prior to the installation of the subfloor, floor covering, or any underlayment, be sure to account for this expected height difference. For the disabled and elderly, 15 inches above the top of the floor covering is usually considered the lowest standard height, but they can be as high as required. Residents in wheelchairs may benefit from slightly higher outlet boxes, with the bottom of the box no less than 15 inches above the floor.
On countertop outlets, it is standard to install outlet boxes so the tops are between 15 and 20 inches from the countertop surface. Make sure all outlet boxes are set at exactly the same height, since these outlets will be highly visible.
Individually measuring each outlet height with a tape measure is one way to set outlet heights. However, there are a few other tricks you might wish to try to speed up the process:
Measure With a Laser Level
Determine your preferred box height and make a single mark on any stud. With a laser level placed on the other side of the room, shoot a line across the entire length of the wall you are working on. Work off this line as you place each box or, to preserve batteries, make pencil marks on studs and then shut off the laser level.
Measure With a Drywall Square
This quick method works best before the floor covering is already installed. If you have a drywall square, place the long end of the square's "T" perpendicular to the floor. Hold the longest part of the square roughly parallel to the floor. Mark a line across four studs by running your pencil along the bottom part of the straightedge. Place the receptacles at this height. This gives you a height of 14 inches. If you then lay a floor, thus raising the floor level, you end up with a height of roughly 12 inches above the floor.
Measure With a Hammer
Most 16-ounce hammers are about 13 inches long. Set the hammer on the floor with the head down, then set the box on top of the hammer handle, resulting in a roughly 12-inch high outlet height after the floor covering is installed.
Standard Height for Light Switch Boxes
The standard height for wall switches in most rooms (excluding those over kitchen counters) is 48 inches above the top of the floor covering (measured to the bottom of the box). For wheelchair users, 48 inches is usually specified as the maximum height, since higher levels can be difficult to reach when sitting in a wheelchair. In these situations, it is fine to position them slightly lower—with the bottom of the box 44 inches above the floor, for example).
Measure With a Story Pole
One free item that is easy to make and which helps you set multiple light switch heights is a story pole. A story pole is a homemade tool that's nothing more than a piece of scrap two-by-four clearly marked with any height you need. You need to measure only once—when you first make the story pole. You can use a single story pole for all of your box heights, and you can even mark different heights (outlets and light switches) on the same story pole. It helps to outline both the top and bottom of the wall box on the story pole, to avoid confusion when marking studs.
Simply stand up the pole next to a wall stud and mark the stud at the appropriate height. Make sure to mark the pole clearly. Notes like "bottom of outlet box" and "center of switch box" help prevent mistakes.
When you are finished with your project, store the pole for later use or recycle it for use as a building material.