Lumens Calculator
Find how many lumens a room needs to be well lit. Enter the size of the room and choose the room type, such as a living room, kitchen, or bathroom, to see the total lumens. Add the lumens printed on your bulbs or fixtures to see how many you need. It works as a lighting calculator for room lighting in any room of your home. To place recessed lights on a grid, use the Recessed Lighting Calculator.
Add another rectangle for an L-shaped room, or subtract areas that don't need light.
- Choose US or Metric. You can still change the unit of any single field.
- Enter the Length and Width of the room. If you know the floor area, choose Known area as the shape and enter it. For an L-shaped room, add a rectangle for each part. Set a section to Subtract for areas you won't light, such as a built-in closet.
- Choose the Room type. To use your own light level, choose Custom light level and enter it in fc or lux.
- Optionally, enter the Lumens per fixture from the bulb or fixture box to see how many fixtures you need.
Length fields accept whole numbers, decimals, fractions, and mixed
numbers, such as 12, 10.5, 1/2, or
6 1/2. Choose ft + in as the unit to enter a
length such as 12 ft 6 in in two fields.
How many lumens a room needs
The light level on a surface is the lumens that land on it, spread over its area. A foot-candle (fc) is 1 lumen per square foot, and a lux is 1 lumen per square meter (as NIST's Guide to the SI defines it), so 1 fc is about 10.76 lux. To light the whole floor to a set level, you need that level × the floor area in lumens:
Total lumens = light level × floor area
Fixtures = total lumens ÷ lumens per fixture, rounded up
Use fc with square feet and lux with square meters. A fixture with several bulbs, such as a ceiling fan with 3 bulbs, gives the lumens of one bulb × the number of bulbs, so enter that as the lumens per fixture. Compare bulbs by the lumens on the box, not the watts. How many lumens you get from a watt depends on the bulb.
The calculator adds the sections set to Add and subtracts those set to Subtract. Each section's area is multiplied by its Quantity. The area of each shape is calculated as follows:
| Shape | Area |
|---|---|
| Rectangle | length × width |
| Known area | the area you enter |
Light levels by room
The room types use the recommended residential lighting levels in Penn State's course notes for EGEE 102, How Much Lighting is Needed, which gives them as the Illuminating Engineering Society's guidance for the rooms in a home. The calculator uses the top of each range:
| Room type | Typical range | Used |
|---|---|---|
| Living room | 10–20 fc (108–215 lux) | 20 fc (215 lux) |
| Bedroom | 10–20 fc (108–215 lux) | 20 fc (215 lux) |
| Kitchen | 30–40 fc (323–431 lux) | 40 fc (431 lux) |
| Dining room | 30–40 fc (323–431 lux) | 40 fc (431 lux) |
| Bathroom | 20–50 fc (215–538 lux) | 50 fc (538 lux) |
| Home office | 20–50 fc (215–538 lux) | 50 fc (538 lux) |
| Hallway or entry | 5–20 fc (54–215 lux) | 20 fc (215 lux) |
| Garage | 30 fc (323 lux) | 30 fc (323 lux) |
The top of the range leaves room for the light that never reaches the floor. A light that's too bright can be dimmed, but a dim one can't be made brighter. To use the low end instead, choose Custom light level and enter it.
These are guides, not rules. How much light you want depends on taste, on age (older eyes need more light), and on how dark the walls are. The same notes also list brighter levels for work surfaces: 50–100 fc for the stove and sink, and 100 fc for a garage workbench. To light just that surface, enter its own area and the level as a Custom light level. For an office, a store, or outdoors, enter the level you need the same way.
Light lost before it reaches the floor
The result is the light that reaches the floor. Some of the light from each fixture never gets there: shades and frosted covers absorb part of it, dark walls and ceilings absorb more, and fixtures get dimmer as they age and collect dust. Lighting designers allow for this with factors from each fixture's data, so the calculator doesn't. If the walls or ceiling are dark, or the fixtures have shades, plan for more lumens. Round up the number of fixtures, or choose dimmable ones and turn them down if the room is too bright.
Examples
A 12 × 15 ft living room
The floor is 12 × 15 = 180 ft², and a living room uses 20 fc, so you need 180 × 20 = 3,600 lumens. With 800 lumen bulbs, that's 3,600 ÷ 800 = 4.5, rounded up to 5 bulbs.
A 10 × 12 ft kitchen
A kitchen uses 40 fc, so 120 ft² × 40 = 4,800 lumens, or exactly 6 fixtures of 800 lumens.
An L-shaped room
A 12 × 15 ft living room with a 6 × 8 ft nook is 180 + 48 = 228 ft², so you need 228 × 20 = 4,560 lumens.
A Metric bedroom
A 5 × 3 m bedroom is 15 m², or about 161.46 ft², so at 20 fc you need about 161.46 × 20 = 3,229 lumens. That's the same as 15 m² × 215.28 lux. With 1,000 lumen fixtures, that's 4 fixtures.
FAQ
About 2,880 lumens for a living room or bedroom: 144 ft² × 20 fc. A kitchen or dining room at 40 fc needs about 5,760, and a bathroom or home office at 50 fc about 7,200.
About 40 lumens per square foot (40 fc) for the whole kitchen, so a 10 × 12 ft kitchen needs about 4,800 lumens. Over the stove and sink, 50 to 100 fc is common.
It's 1 lumen per square foot, a unit of light level. 1 fc is about 10.76 lux, and a lux is 1 lumen per square meter.
By lumens. Watts measure the power a bulb uses, and an LED gives far more lumens per watt than an old incandescent bulb. The lumens are printed on the box.
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