How to use the recessed light spacing calculator
- Enter the room length and room width in feet.
- Choose how to set the spacing. A spacing I enter uses your number in feet. Ceiling height uses a share of the ceiling height, which you can edit.
- Optionally enter the watts per light to see the total wattage.
- Read the number of lights, the layout, the real spacing and the distance from the walls.
Formula
Lights along the length = room length / spacing, rounded up
Lights along the width = room width / spacing, rounded up
Actual spacing = room size / number of lights each way, and each light sits half a spacing from the wall
Total lights = lights along the length x lights along the width
With the ceiling height option, spacing = ceiling height x share / 100. The 50% share is a rule of thumb you can change, not a requirement.
A 12 by 16 foot room at 4 foot spacing
A room 16 feet long and 12 feet wide with 4 foot spacing needs 16 / 4 = 4 lights along the length and 12 / 4 = 3 along the width. That is 3 rows of 4, or 12 lights. Each light is 2 feet from its nearest wall, and there is 16 square feet of room per light.
A 13 by 10 foot room at the same spacing rounds up to 4 by 3 as well, so 12 lights, but the actual spacing stretches to 3.25 feet along the length and 3.33 feet along the width. An 8 foot ceiling with the 50% rule gives 4 feet, and a 9 foot ceiling gives 4.5 feet, which still rounds up to the same 12 lights.
A rule of thumb, not a design
One way to space recessed lights is to relate the distance between them to the ceiling height, so a higher ceiling gets wider spacing. The share in this tool is yours to change, and the result is a starting layout, not a lighting design.
How bright the room feels depends on the lumens of each fixture, the beam angle, the color of the walls and the use of the room. A kitchen counter or a reading chair may want more light than a hallway of the same size.
Practical limits
The grid is even and ignores joists, ducts, pipes and fixtures that need clearance. Real layouts are often shifted to avoid them or to line up with furniture. Electrical work should follow your local code and be done by a qualified person.
For light output, the lighting lumens calculator turns room size into lumens. To estimate running cost use the electricity cost calculator, to work out room area try the square footage calculator, and for even spacing of other items see the shelf spacing calculator.
Assumptions and limits
- The room is a rectangle and lights form an even grid.
- Spacing is either a number you enter or a share of ceiling height that you can edit.
- Lights are placed half a spacing from each wall.
- Joists, ducts, brightness and code requirements are not considered.
Frequently asked questions
How many recessed lights do I need for a room?
Divide each room dimension by the spacing, round up, and multiply the two results. A 16 by 12 foot room at 4 foot spacing needs 4 x 3 = 12.
How far apart should recessed lights be?
There is no single rule. One starting point relates the spacing to the ceiling height, and the tool lets you set the share or type a spacing directly.
How far should recessed lights be from the wall?
In this layout each light sits half a spacing from the wall, so 4 foot spacing puts lights 2 feet out. You can shift them to suit the room.
Does the tool tell me how bright the room will be?
No. Brightness depends on the fixture's lumens and the room, which this tool does not model. Use a lumens estimate for that.