Recessed Lighting Calculator

About the Recessed Lighting Calculator

Recessed lights, also called can lights, pot lights or downlights, sit flush with the ceiling and give clean, even general lighting without fixtures hanging in the way. The most common question when planning them is simply how many a room needs. Too few leaves dim corners; too many wastes money, makes the ceiling look like a colander and can make a room uncomfortably bright.

This recessed lighting calculator answers the question with lumens, the measure of light output. It multiplies the room's area by a target light level for that type of room, divides by the lumens of the fixture you plan to use, and rounds up. It also shows the total lumens, the resulting light level in foot-candles and the total wattage.

How to Use the Recessed Lighting Calculator

Enter the room length and width in feet.

Choose the room type, which sets the target lumens per square foot.

Enter the lumens per light and watts per light from the fixture's packaging.

The Formulas

  lumens needed = length × width × lumens per ft² for the room
  lights        = ⌈lumens needed ÷ lumens per light⌉
  foot-candles  = lights × lumens per light ÷ area
  watts         = lights × watts per light

Targets used, in lumens per square foot: living room 15, bedroom 12, kitchen 35, bathroom 50, home office 40 and hallway 8.

Step-by-Step Example

A 15 × 12 ft kitchen with 800-lumen, 10-watt LED downlights.

  area       15 × 12 = 180 ft²
  needed     180 × 35 = 6,300 lumens
  lights     6,300 ÷ 800 = 7.9 → 8 lights
  delivered  8 × 800 = 6,400 lumens ≈ 36 foot-candles
  power      8 × 10 = 80 W

Lumens, Not Watts

With incandescent bulbs, people judged brightness by watts. LEDs produce far more light per watt, so watts no longer say much about brightness. Lumens do. A typical 4-inch LED downlight gives about 600 to 700 lumens, and a 6-inch one 800 to 1,000, using only 9 to 15 watts. The old rule of a 65-watt flood bulb in each can gave about 650 lumens. Always plan by lumens and use watts only to estimate running costs.

Foot-Candles and Room Use

A foot-candle is one lumen falling on one square foot. Different activities need different amounts of light. Relaxing and watching television needs relatively little, around 10 to 20 foot-candles. Cooking, reading, homework and desk work need more, 30 to 50. Bathrooms, where people shave and apply makeup, benefit from bright, even light. The targets in this calculator are for general, or ambient, lighting. Task lighting such as under-cabinet strips and vanity lights adds to them where the work happens.

Layering Light

Recessed lights work best as one layer of a lighting plan. Pendants over an island, under-cabinet lights along worktops, wall sconces and table lamps add light where it is needed and give a room depth. Relying on downlights alone can make a room feel flat and create shadows under cabinets and faces. If you plan other lighting, you can reduce the room target slightly.

Ceiling Height and Beam Angle

The calculation assumes a standard 8 to 9 ft ceiling. Higher ceilings put the lights further from the floor, so less light reaches it; choose brighter fixtures or more of them. The beam angle also matters: a narrow beam concentrates light into pools, while a wide beam spreads it more evenly. For general lighting, beam angles of 60° or more are usual.

Colour Temperature and Dimming

Colour temperature affects how a room feels. Warm white, 2,700 to 3,000 K, suits living spaces and bedrooms; neutral white, 3,500 to 4,000 K, suits kitchens, bathrooms and work areas. Many modern downlights let you switch colour temperature. Fit dimmers wherever possible, so the same lights can be bright for cleaning and soft for evenings.

Energy Use and Running Cost

LED downlights use very little power. Eight 10-watt lights draw 80 watts in total, less than a single old incandescent floodlight. Used for five hours a day, that is about 146 kilowatt-hours a year, roughly $22 at 15 cents per kilowatt-hour. Swapping old halogen or incandescent cans for LED retrofit modules often pays for itself within a couple of years and greatly reduces heat in the ceiling.

Planning Circuits

Recessed lights are usually grouped on one or more switched circuits. Splitting a large room into zones, for example the kitchen worktops and the dining area, gives more control. Each lighting circuit has a limit on the total load, which LED fixtures rarely approach, but switches and dimmers must be rated for LED loads to avoid flicker and buzzing. Check that the dimmer is compatible with the fixtures you choose.

Bathrooms and Showers

Fixtures over showers and tubs must be rated for wet or damp locations, usually with a sealed lens trim. Many codes also limit the type of fixture allowed within a set distance of a bath. Use the bathroom setting for general light, and add mirror or vanity lights so faces are lit from the front rather than from above.

Understanding Your Result

The headline gives the number of recessed lights.

The working line shows the area, target and lumens per light.

The total line gives total lumens, foot-candles and watts.

When Should You Use This Calculator?

Use it when planning lighting for a renovation or new build.

Use it to compare fixtures with different lumen outputs.

Use it to check whether an existing room is under-lit.

Common Mistakes

Choosing fixtures by watts. Compare lumens.

Using the same count for every room. Kitchens need more light than bedrooms.

Ignoring task lighting. Downlights cannot light under cabinets.

Skipping dimmers. Bright light is not always wanted.