How many lumens does a room need?
Pick a light level for the job, enter the room size, and get the lumens to install.
This is a screening tool, not a lighting design or a safety assessment. Workplace lighting, egress lighting and emergency lighting must follow the rules that apply to your building; ask a qualified lighting designer or electrician. How we check our calculators.
The Department of Defense (UFC 3-530-01) and OSHA values are shown as printed. They are ambient design targets, not the Illuminating Engineering Society's recommendations, which are in a paid handbook.
CU comes from the fixture's photometric data for your room; 0.6 is only an example. UFC 3-530-01 gives 0.81 as a typical LLF for an office with LED fixtures.
What the number means
Lighting a room is a budget of light. The levels people recommend are in foot-candles (lumens per square foot) or lux (lumens per square meter) falling on the work surface; the fixtures are bought in lumens. The lumen method connects the two: it asks how many lumens must leave the fixtures so that, after the room and the years have taken their share, the target level reaches the desk or floor. It gives the average level, which is the right number for sizing the lighting, not for placing each fixture. Use the lumens to watts calculator afterwards to compare bulbs.
The formula
Lumens = E × A ÷ (CU × LLF), where E is the target illuminance, A the floor area (or the work-plane area), CU the coefficient of utilization and LLF the light loss factor. E and A must use the same system: foot-candles with square feet, or lux with square meters. CU (0 to 1) is the share of the fixtures' lumens that reach the work plane; LLF (0 to 1) is the share left after lamp dimming, dirt and aging. With CU 0.6 and LLF 0.81 you must install 2.06 lumens for every lumen you want on the desk.
Worked example
A small office is 200 sq ft and should have 30 foot-candles, the UFC 3-530-01 target for offices. With CU 0.6 and LLF 0.81: 30 × 200 ÷ (0.6 × 0.81) = 12,346 lumens. In metric, 30 fc is 323 lux, and 323 lux over 18.6 m² gives the same 12,346 lumens. Four 4,000 lumen troffers give 16,000 lm and an average of about 39 fc at the desk. For a 600 sq ft shop worked at the task level of 50 fc the same factors call for 61,728 lumens. The calculator opens with the office case.
Limits of this method
- An average, not a floor plan. The result says how much light the room needs in total, not where it lands. A room can meet the average and still have dark corners; UFC 3-530-01 asks for a ratio of average to minimum of at most 2:1 in open offices and 3:1 in maintenance shops.
- CU is not a guess. It depends on the fixture and the room's proportions and surface colors. Taking 1.0 would leave the room dark; the manufacturer's data sheet is the source. The example value 0.6 is not a standard.
- Targets are for ambient light. UFC 3-530-01 states its targets are general ambient lighting; task lights and decorative lighting are in addition. Its housing values are low (a few foot-candles for bedrooms and living rooms), because they are Department of Defense design minimums, not what most households want. Use the "Other" choice for a higher level.
- OSHA's table is a floor. The construction minimums of 3 to 30 foot-candles apply "while any work is in progress"; other areas are referred to a national industrial lighting standard (ANSI A11.1-1965, as OSHA cites it). Do not read them as comfort recommendations.
- Egress and emergency lighting follow separate rules. Fire and building codes set minimums for exits and emergency power that this page does not cover.
Common questions
How many lumens do I need for a room?
Multiply the light level you want by the floor area, then divide by the coefficient of utilization and the light loss factor: lumens = E × A ÷ (CU × LLF). For a 200 sq ft office at 30 foot-candles, with CU 0.6 and LLF 0.81, that is 12,346 lumens. Only 6,000 lumens would arrive at the desk if nothing were lost, so ignoring CU and LLF would give the room only about 49% of the light it needs.
What is the difference between lumens, foot-candles and lux?
Lumens measure the light a source gives off; foot-candles and lux measure how much of it lands on a surface. One foot-candle is one lumen on each square foot, and one lux is one lumen on each square meter, so 1 fc = 10.764 lux and 30 fc is about 323 lux. A bulb's watts are only its electrical power; for LEDs the lumens on the box are what to compare. See the <a href="/lumens-to-watts-calculator/">lumens to watts calculator</a> for the conversion.
What is the coefficient of utilization?
The UFC 3-530-01 glossary defines the coefficient of utilization as the ratio of the light received on the work plane to the total light emitted by the sources alone, the product of the room utilization factor and the luminaire's efficiency. In plain terms it is the share of the lamp's lumens that actually reach the desk or floor. It depends on the fixture type, the mounting height, the shape of the room and the reflectance of the walls and ceiling, so the manufacturer publishes it in the fixture's photometric data. Tall, narrow rooms and dark walls give lower values. Check the data sheet; this calculator does not guess it.
What is the light loss factor?
The light loss factor, formerly called the maintenance factor, is the ratio of the light you get in service to the light you would get if the lamps gave their initial rated lumens and nothing aged. It accounts for dimming of the light source, dirt on fixtures and room surfaces, and similar losses. UFC 3-530-01 gives a typical value of 0.81 for an office with LED luminaires that are L80 at 60,000 hours over a 25-year building life, and says it varies with environment, application, LED depreciation and life cycle. Dusty or greasy spaces need a lower number.
What light levels should I design for?
It depends on the task. OSHA's construction rule (29 CFR 1926.56) sets minimums of 3 foot-candles for excavation and active storage areas, 5 for general construction area lighting and indoor corridors and warehouses, 10 for shops and equipment rooms, and 30 for offices and first aid stations, and sends other areas to the national standard on industrial lighting. The Department of Defense's UFC 3-530-01 gives design targets such as 5 fc for corridors, 30 fc for offices, 40 fc for classrooms, 20 fc for mechanical rooms and 50 fc at task areas in maintenance shops. The Illuminating Engineering Society's recommendations, which most designers use, are in a paid handbook and are not reproduced here.
How many fixtures does that take?
Divide the lumens needed by the lumens each fixture gives off. The office needs 12,346 lumens, so 4 fixtures of 4,000 lumens each give 16,000 lm and an average of about 39 fc, a little above the target. Spacing matters too: the lumen method gives an average, and fixtures should be spread so that the darkest spot is not far below it. UFC 3-530-01 asks for no more than 2 to 1 between average and minimum in an open office and 3 to 1 in a maintenance shop.
This is a screening tool, not a safety assessment. Good lighting also means glare control, color quality and the right controls; have a qualified lighting designer or electrician plan work lighting, egress and emergency lighting.
Sources: OSHA, 29 CFR 1926.56, Illumination, table D-3 (eCFR text, read October 27, 2026); U.S. Department of Defense, Unified Facilities Criteria UFC 3-530-01, Interior and Exterior Lighting Systems and Controls (February 9, 2023, Change 1, December 15, 2023), chapter 3 (targets), section 3-2 (typical LLF) and glossary (CU, LLF); the Illuminating Engineering Society's handbook was not used (paid). Where UFC 3-530-01 prints a foot-candle and a lux value that disagree, that row is not used. Related: lumens to watts calculator, ventilation rate calculator, sound distance calculator. How we check our calculators.