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Room Lighting & Lumen Calculator
Calculate the total lumens and number of lamps a room needs from its area and the target lux for its function. From lumens or LED watts. Free.
Lumens measure a lamp's total light, lux is lumens per m² (brightness in the room), and watts are just power draw — not a brightness measure. This calculator turns target lux into a lumen need, then a lamp count.
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Layout note
A planning estimate; actual results depend on fixture layout, ceiling height, interior colors, and lamp type. High ceilings or dark walls need more lumens.
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Visit StoreUnderstanding lumens, lux & watts
Lumens, lux, and watts
Lumens = a lamp's total light. Lux = lumens per m² (how bright the work surface is). Watts = power draw. A 9-watt LED can make ~800 lumens — far brighter per watt than incandescent.
Target lux per function
Each room needs different brightness: bedroom ~120–150 lux, kitchen ~250–300 lux, work room ~300–500 lux. Multiply target lux by area for the total lumens needed.
Utilization & maintenance factors
Some light is lost to walls/ceiling and lamps dim over time. A combined factor (~0.7) makes the calculation more realistic in advanced mode — slightly increasing the lamp count.
FAQ
Frequently asked questions
How do I calculate a room's lighting need?
Multiply room area (m²) by its target lux to get the total lumens needed. Then divide by lumens per lamp (from packaging, or watts × efficacy). Round up for the lamp count.
How many watts of light for a bedroom?
A bedroom needs ~120–150 lux. A 12 m² room needs about 1,560–1,800 lumens. At ~90 lm/watt LED, that's ~18–20 watts total — e.g. 2–3 nine-watt LEDs, spread evenly for uniform light.
What's the difference between lumens, lux, and watts?
Lumens are a lamp's total emitted light. Lux is lumens landing per m² (room brightness). Watts are power draw — not brightness. To judge brightness, look at lumens, not watts.
How do I calculate a room's lux?
Lux = total lumens of all lamps ÷ room area (m²). With several lamps, sum their lumens then divide by area. This calculator works in reverse: from target lux it computes the lumens and lamps needed.
Why can actual results differ?
Because fixture layout, ceiling height, wall color, and lamp type affect the light that actually arrives. High ceilings or dark walls absorb more. Use advanced mode for a more conservative result.
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