Calculator

Lumens calculator

Pick the room, enter its size and the bulbs you plan to use. The calculator multiplies the recommended light level for that room by its floor area, gives the lumens as a range, and lays the bulbs out on a ceiling plan.

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Lumens calculator

Feet and inchesMetres

Room

Recommended: 10–20 fc of general light.

Room length

Room width

Bulb output (and the old incandescent it matches)

450 lm (40 W)800 lm (60 W)1,100 lm (75 W)1,600 lm (100 W)

Foot-candles × area is the light that should reach the room. Shades, dark walls and deep fixtures swallow some of what the bulbs give out, so plan towards the top of the range and put the lights on a dimmer.

Lumens needed

1,680–3,360 lm

168 ft² at 10–20 fc · 3–5 bulbs of 800 lm

Bulbs: 3–5
Light level: 10–20 fc
Per bulb: 800 lm
Floor area: 168 ft²

Ceiling plan

5 fixtures, for the top of the range

This room's size, by use

lm, range and midpoint

Living room2,520 lm
Bedroom2,520 lm
Kitchen5,880 lm
Bathroom5,880 lm
Home office5,880 lm
Dining room5,880 lm
Hallway2,100 lm

Open as a floor plan

The formula

Light level: the recommended illuminance for the room, in foot-candles (fc). A living room or bedroom is 10 to 20 fc of general light; a kitchen 30 to 40.
Floor area: length × width, in ft².
Lumens = foot-candles × ft². A foot-candle is one lumen per square foot, so the units cancel. In metric, lumens = lux × m², and 1 fc = 10.764 lux.
Bulbs: lumens ÷ the lumens on the bulb's box, rounded up, for each end of the range.

Sources and assumptionsThe light levels are the Illuminating Engineering Society's residential guidance as tabled in Penn State's course EGEE 102, "How much lighting is needed" (read 11 October 2026): living rooms and bedrooms 10–20 fc, kitchen (general) 30–40, bathrooms 20–50, home office and reading 20–50, dining room 30–40, hallways and entries 5–20. The current IES document for homes is ANSI/IES/ALA RP-11-26, which is sold, not published free; laundry rooms are not in the table we could cite, so they are left out. Bulb outputs are the minimum lumens in the ENERGY STAR light bulb purchasing guide (16 March 2020): 450 lm for a 40 W incandescent, 800 for 60 W, 1,100 for 75 W and 1,600 for 100 W. The formula counts the light that should reach the room and ignores what shades, fixtures and dark surfaces absorb, which is why planning towards the top of the range is safer.

Worked example

A 14 × 12 ft living room is 168 ft². At 10 to 20 fc it needs 168 × 10 = 1,680 to 168 × 20 = 3,360 lumens. With 800 lm bulbs (the old 60 W), that is 1,680 ÷ 800 = 2.1, so 3 bulbs for the low end, and 3,360 ÷ 800 = 4.2, so 5 bulbs for the high end. Five on a dimmer covers both.

A 12 × 12 ft kitchen is 144 ft² at 30 to 40 fc: 4,320 to 5,760 lumens, 6 to 8 bulbs of 800 lm or 4 to 6 of 1,100 lm, before any task lights under the cabinets. In metric, a 4 × 3 m bedroom is 12 m² at 108 to 215 lux: about 1,292 to 2,583 lumens.

Lumens for common rooms with 800 lm bulbs (worked with the calculator)
Room	Size	Light level	Lumens	800 lm bulbs
Bedroom	10 × 10 ft	10–20 fc	1,000–2,000	2–3
Bedroom	12 × 12 ft	10–20 fc	1,440–2,880	2–4
Living room	14 × 16 ft	10–20 fc	2,240–4,480	3–6
Kitchen	10 × 12 ft	30–40 fc	3,600–4,800	5–6
Dining room	12 × 14 ft	30–40 fc	5,040–6,720	7–9
Bathroom	5 × 8 ft	20–50 fc	800–2,000	1–3
Home office	10 × 10 ft	20–50 fc	2,000–5,000	3–7
Hallway	3½ × 12 ft	5–20 fc	210–840	1–2

Layers of light

General light is what this calculator sizes: ceiling fixtures, recessed lights or a central pendant that light the whole floor.
Task light goes where the work is: under-cabinet strips over a counter, a vanity light at the mirror, a desk lamp. Penn State's table gives 50 to 100 fc at a kitchen's stove and sink, well above the room's general level.
Dimmers let one layout serve both ends of a range, bright for cleaning and low in the evening. Check that the bulbs are sold as dimmable.
Even spacing matters as much as the total: a grid of smaller lights gives fewer shadows than one bright fixture in the middle. The ceiling plan above spaces them evenly.

Plan the lights on the plan

In a FloorGen plan every room already has its area. Open the room from the calculator, place the fixtures where the ceiling plan shows them, and add the switches by the doors.

Questions

How many lumens do I need for a 12 × 12 bedroom?

A 12 × 12 ft bedroom is 144 ft². At the 10 to 20 foot-candles recommended for bedrooms, that is 1,440 to 2,880 lumens: two to four 800 lm bulbs.

How many lumens per square foot for a kitchen?

About 30 to 40 lumens per square foot of general light, since a foot-candle is a lumen per square foot. Add task lighting over the counters, the stove and the sink.

How many lumens is a 60 watt bulb?

At least 800 lumens, by ENERGY STAR's guide. An LED bulb gives the same light for far fewer watts, so compare the lumens on the box, not the watts.

What is the difference between lux and foot-candles?

Both measure light falling on a surface. A foot-candle is one lumen per square foot; a lux is one lumen per square metre. One foot-candle is 10.764 lux.

Does ceiling height change the lumens?

The formula counts the light that should reach the room, so a tall ceiling does not change the target, but light from a higher fixture spreads and falls off on the way down. In a tall room, aim for the top of the range or use fixtures that direct their light downwards.