Room Lighting & Lumens Calculator
Pick a room use and enter dimensions or floor area in feet or meters. Estimate a starting lumen range and bulb count, then account for fixture placement, shades and the light you already have.
Reference table
Lumens Per Square Foot by Room
A foot-candle is one lumen per square foot, so each foot-candle range is also the lumens to plan for every square foot of floor.
| Room or use | Foot-candles (lm/sq ft) | Lux (lm/m²) | Lumens per 100 sq ft | Good to know |
|---|---|---|---|---|
| Living room | 5–30 | 54–323 | 500–3,000 | Lamps can supply the top end |
| Bedroom | 5–30 | 54–323 | 500–3,000 | Top end is for reading in bed |
| Dining room | 5–10 | 54–108 | 500–1,000 | Aim the light at the table |
| Kitchen, general | 5–30 | 54–323 | 500–3,000 | Add counter light separately |
| Kitchen counters | 30–50 | 323–538 | 3,000–5,000 | Enter the counter area, not the floor |
| Bathroom | 10–30 | 108–323 | 1,000–3,000 | Top end belongs at the mirror |
| Home office | 30–50 | 323–538 | 3,000–5,000 | A desk lamp can supply the top end |
| Hallway or stairs | 5–10 | 54–108 | 500–1,000 | Light every step evenly |
Low end: the IES general level for the space; high end: its main task. Residential rows of the IESNA Lighting Handbook, 9th edition; dining, bathroom and hallway bounds from the 10th edition. Lux converted at 1 fc = 10.764 lux. For adults aged 25 to 65; the IES doubles targets for older eyes.
Bulb brightness
Lumens vs Watts for Common Bulbs
The US Department of Energy’s rule of thumb for replacing incandescent bulbs, and the floor one bulb lights at living-room levels (5–30 fc).
| Bulb brightness | Replaces an incandescent | Floor it lights at 5–30 fc | Good to know |
|---|---|---|---|
| 450 lm | 40 W | 15–90 sq ft | A 12 × 12 ft living room takes 2–10 bulbs |
| 800 lm | 60 W | 27–160 sq ft | A 12 × 12 ft living room takes 1–6 bulbs |
| 1,100 lm | 75 W | 37–220 sq ft | A 12 × 12 ft living room takes 1–4 bulbs |
| 1,600 lm | 100 W | 53–320 sq ft | A 12 × 12 ft living room takes 1–3 bulbs |
Assumes all of a bulb’s light reaches the floor. Shades, dark walls and tall ceilings keep some of it back, so round up rather than down.
From Floor Area to Bulbs
Start With the Floor Area
Lumens are floor area times a target level. Enter the length and width, or a floor area from a plan, and the calculator multiplies it by the room’s range in foot-candles or lux. The working shows each step so you can check it.
Calculate Your RoomSplit the Light Into Layers
One ceiling fixture rarely suits every task. Let ambient light cover the low end of the range, then add task lamps where people read, cook or shave, and accent light for art. Switch each layer separately.
See Your Low and High EndMatch the Level to the Task
A living room used for TV needs far less light than one used for reading. Pick the use, not just the room: kitchens have a general setting and a counters setting, and bathrooms need the most light at the mirror.
Try Another Room UseCount Bulbs by Lumens
Watts measure energy, not light. Choose a bulb step, from 450 lm (the old 40 W) to 1,600 lm (100 W), or type the lumens on your box. The calculator divides and rounds up to whole bulbs.
Count Your BulbsHow to Calculate How Many Lumens for a Room
Multiply floor area by a target level, then divide by the lumens per bulb. A 12 × 12 ft bedroom at 5–30 fc needs 720–4,320 lumens.
- 1
Find the floor area
Measure the length and width wall to wall and multiply them for square feet, or use meters for square meters. Split an L-shaped room into two rectangles and add them.
- 2
Multiply by the target level
Foot-candles are lumens per square foot, so square feet times the room’s foot-candle range gives the lumens to aim for. In metric, multiply square meters by lux.
- 3
Divide by the lumens per bulb
Divide each end of the range by the lumens printed on the bulb box and round up. Fixtures on a dimmer can then cover both ends.
Where a Lumen Count Helps
Planning recessed lights
Divide the room’s lumens by one downlight’s output to get a count, then space them evenly. Downlights vary, so check the lumens on the fixture’s spec sheet.
Replacing old bulbs
Watts no longer say how bright a bulb is. Find the lumen step that replaces your old bulb, then check that the room’s total still lands inside its range.
Choosing wall colors
Light walls reflect more light back into a room and dark ones absorb it. With dark paint or wood paneling, plan toward the top of the range.
FAQ
Lumens Calculator Questions
Multiply the floor area in square feet by the room’s foot-candle target. A 12 × 12 ft living room is 144 sq ft; at 5–30 fc that is 720–4,320 lumens. In metric, multiply square meters by lux instead.
About 5–30 for living rooms, bedrooms and general kitchen light, 30–50 at kitchen counters and desks, and 5–10 in hallways. A lumen per square foot is a foot-candle, so these are the IES foot-candle targets.
A 12 × 12 ft room is 144 sq ft. A bedroom or living room needs 720–4,320 lumens, a dining room 720–1,440 and a home office 4,320–7,200. With 800 lm bulbs, the bedroom takes 1–6 bulbs.
About 800 lumens. The US Department of Energy’s rule of thumb is 450 lm for a 40 W bulb, 800 lm for 60 W, 1,100 lm for 75 W, and 1,600 lm for 100 W. Energy-saving bulbs reach them with fewer watts.
Less light reaches the back of the eye with age, and glare gets harder to handle. The IES doubles its targets when at least half the people using a space are over 65; the calculator’s age switch does the same. Add the light without glare: shaded lamps, light walls.
Yes. The calculator counts the light that should reach the floor. Tall ceilings, dark walls and heavy shades absorb part of a bulb’s output before it gets there, so plan toward the top of the range or add a fixture. Light walls help.
Yes, if the bulbs are made for dimming; the box says “dimmable.” LED dimming varies, so check the dimmer maker’s compatibility list. A dimmer lets one fixture sized for the high end also give you the low end.
The targets are Illuminating Engineering Society recommendations: residential rows from the IESNA Lighting Handbook, 9th edition, plus dining, bathroom and hallway values from the 10th edition. The bulb steps come from the US Department of Energy. Treat them as starting points, not rules.