Lumens to Lux Calculator
Convert light output (lumens) to illuminance (lux) over an area — and back.
Reviewed by the ToolNestr Editorial Team — July 2026
Calculator
Illuminance
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The formula
The relationship between luminous flux and illuminance is straightforward:
Lux = Lumens ÷ Area (m²)
Calculates illuminance from total light output
Lumens = Lux × Area (m²)
Finds required light output for a target lux
Worked example
A room measures 10 m² and you install a light bulb that produces 2,000 lumens. The illuminance at the floor (assuming even distribution) is:
lux = 2,000 lm ÷ 10 m² = 200 lux
Conversely, if you need 300 lux in a 15 m² living room, the required light output is:
lumens = 300 lux × 15 m² = 4,500 lm
Use cases
Room lighting design
Determine how many lumens you need from bulbs to achieve comfortable illuminance for living rooms, kitchens, bedrooms, and hallways. Plan the total wattage and number of fixtures required.
Photography & video
Studio lighting requires specific lux levels for correct exposure. Use the calculator to determine how many lumens your strobes or continuous lights must produce at a given distance.
Flashlight / torch performance
Compare flashlights by converting their lumen rating into useful lux at a typical working distance. A 1,000-lumen light spread over 5 m² gives only 200 lux.
Workplace compliance
Health and safety regulations specify minimum lux for offices, workshops, and warehouses. Use the tool to verify your lighting installation meets required standards.
| Space / task | Recommended lux | Example lumens (20 m²) |
|---|---|---|
| Warehouse / storage | 100–200 | 2,000–4,000 lm |
| Living room (ambient) | 100–300 | 2,000–6,000 lm |
| Living room (task) | 300–750 | 6,000–15,000 lm |
| Office / classroom | 300–500 | 6,000–10,000 lm |
| Workshop / garage | 500–1,000 | 10,000–20,000 lm |
| Surgical / operating room | 10,000–20,000 | 200,000–400,000 lm |
| Photography studio | 1,000–5,000 | 20,000–100,000 lm |
| Outdoor / street lighting | 10–50 | 200–1,000 lm |
Lumen estimates assume even light distribution over 20 m². Actual requirements vary with ceiling height, wall colour, and fixture placement.
How lighting calculations work
Lumens (lm) measure the total amount of visible light emitted by a source — this is the "light output" you see on bulb packaging. Lux (lx) measures illuminance, or how much of that light actually lands on a one-square-metre surface. One lux equals one lumen per square metre. The distinction is critical: a 2,000-lumen bulb will produce very different lux depending on whether it lights a compact desk or a large warehouse.
In the simplest case — a point light source with uniform distribution — illuminance follows the inverse-square law. Doubling the distance from the source quarters the lux value because the same total lumens now spread over four times the area. Real rooms with reflective walls, directional fixtures, and multiple light sources are more complex, but the fundamental relationship remains: the lux you experience is always the total lumens reaching that surface divided by its area.
The calculator uses the formula lux = lumens ÷ area when working in square metres. When you toggle to the reverse direction, it uses lumens = lux × area to tell you how many lumens a bulb or fixture must produce to hit your target illuminance. This is the same calculation lighting designers perform when specifying fixtures for offices, retail spaces, and studios.
Tips for planning room lighting
Lux drops with distance
Illuminance follows the inverse-square law. If a pendant light is 2 m above the floor, moving it to 4 m reduces the lux at floor level to one-quarter. Always consider mounting height when planning lumens.
Different tasks need different lux
Fine assembly work needs 750–1,500 lux, while a hallway needs only 50–100 lux. Layer your lighting — ambient (general), task (focused), and accent (decorative) — so each area gets the right level without over-lighting the whole room.
Account for light loss
Lumen output drops over a bulb's life (lumen depreciation), and dirt on lenses and walls reduces reflected light. Design for 20–30% more lumens than the bare calculation suggests to maintain adequate lux over time.
Use multiple sources
A single ceiling fixture creates harsh shadows and uneven lux distribution. Spread the required lumens across several lamps — floor lamps, wall washers, and overhead fixtures — for softer, more uniform illuminance.
Check bulb packaging
Modern LED bulbs list both lumens and an equivalent wattage. A typical 800-lm LED bulb replaces a 60 W incandescent. Use the calculator to decide how many bulbs you need rather than relying on wattage alone.
Lux reference by space type
Recommended illuminance levels vary widely depending on the activity. The table above lists common guidelines from lighting standards such as the IES (Illuminating Engineering Society) and CIBSE (Chartered Institution of Building Services Engineers). These values are measured at the work plane — typically desk height (0.75 m) for offices and floor level for general areas.
For precision tasks like jewellery making, electronics assembly, or medical examination, lux levels of 1,500–3,000 are common. For circulation spaces like corridors and stairwells, 50–100 lux is usually sufficient. Designers use the lumen method to calculate the number of fixtures needed: total required lumens divided by the lumens per fixture, adjusted for a utilisation factor (0.5–0.8) that accounts for light lost to walls, ceilings, and absorption.
Colour temperature (measured in Kelvin) also affects how bright a space feels. A 4,000 K cool-white light at 500 lux will appear brighter than a 2,700 K warm-white light at the same lux because the human eye is more sensitive to blue-green wavelengths. When planning lighting, consider both lux level and colour temperature to create comfortable, effective illumination.
Related calculators
Frequently asked questions
What is the difference between lumens and lux?
Lumens measure total light emitted; lux measures light per square metre on a surface.
How many lux for an office?
Commonly 300–500 lux for general office work.
Does distance matter?
Yes — the same lumens spread over a larger area gives fewer lux.
What is a typical living room lux?
Around 100–300 lux for ambient lighting, 300–750 for task lighting.
Sources & references
This tool uses standard formulas and reference values from:
- • NFPA 70 — National Electrical Code (NEC), conduit fill, box fill and conductor ampacity. nfpa.org
- • IPC-2221, Generic Standard on Printed Board Design (trace width / current). ipc.org
- • NIST reference constants and unit definitions; IEEE standards where applicable. nist.gov
For educational and preliminary use. Verify against full engineering calculations and the governing standard before any real design.