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Lighting Illuminance (Lux) Calculator

Calculate the average illuminance a lighting layout provides across a room area.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Average illuminance

200 lux

Check your inputs

This gives an average illuminance across the full area only — it does not account for light distribution pattern, mounting height, fixture spacing uniformity, or surface reflectance, all of which affect actual illuminance at any specific point. Use professional lighting design software for a point-by-point illuminance layout.

With the figures above, the average illuminance comes to 200 lux. Note that illuminated room area sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 200 lux — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Illuminance = total lumens ÷ illuminated area, the basic photometric relationship defining lux (lumens per square meter)

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

What is lux and how is it calculated here?
Lux is lumens per square meter, the basic photometric unit of illuminance. This calculator divides the total lumen output of your fixtures by the illuminated room area to get the average illuminance in lux.
Does this tell me the illuminance at any specific point in the room?
No — this is an average across the full room area only. It does not account for light distribution pattern, mounting height, fixture spacing uniformity, or surface reflectance, all of which affect actual illuminance at any specific point. Use professional lighting design software for a point-by-point layout.
What lux level should I target?
Target lux levels vary widely by space and task (e.g. general living areas need far less than a workshop or reading area) — check a lighting design reference or your local code for the recommended illuminance for your specific application.