Lumen Calculator that sizes room lighting from IES foot-candle targets, counts bulbs, converts lumens to LED watts and lux, and finds how far a light beam of any rating will shine.
Pick the room, enter its size and the rated lumens of the bulb you plan to buy.
Target & Losses
Fixture Layout Plan
Lumens by Room Type
| Room or task | IES range (fc) | Target | Lamp lumens |
|---|---|---|---|
| Living Room or Bedroom | 10–20 | 15 | 2,700 |
| Kitchen, General | 30–40 | 35 | 6,300 |
| Kitchen Task (Stove, Sink) | 50–100 | 75 | 13,500 |
| Dining Room | 30–40 | 35 | 6,300 |
| Bathroom | 20–50 | 35 | 6,300 |
| Home Office or Reading | 20–50 | 35 | 6,300 |
| Hallway or Entry | 5–20 | 12.5 | 2,250 |
| Garage, General | 30 | 30 | 5,400 |
| Garage Workbench or Shop | 100 | 100 | 18,000 |
| General Office | 30–50 | 40 | 7,200 |
| Conference Room | 15–60 | 30 | 5,400 |
| Classroom | 30–50 | 40 | 7,200 |
| Retail Sales Floor | 25–100 | 50 | 9,000 |
| Storage, Bulky Items | 5–20 | 10 | 1,800 |
| Corridor or Stairway | 2.5–10 | 5 | 900 |
| Lunch or Break Room | 5–20 | 15 | 2,700 |
Step-by-Step Math
- Floor area A = 12 ft × 12 ft = 144 ft² (13.38 m²)
- Target E = 15 fc, the midpoint of the IES 10–20 fc range
- Lumens on the work plane = E × A = 15 fc × 144 ft² = 2,160 lm
- LLF × CU = 0.80 × 1.00 = 0.8
- Room cavity ratio = 5 × 5.5 ft × (12 + 12) ft ÷ 144 ft² = 4.58
- Lamp lumens to install = 2,160 lm ÷ 0.8 = 2,700 lm, so bulbs = 2,700 ÷ 800 = 3.38, rounded up to 4
How the Lumen Calculator Works
The Lumen Calculator runs four jobs from one panel. It finds the lamp lumens a room needs, the light level you get from lumens you already have, the LED watts behind a lumen rating, and how far a light beam throws. Each mode shows its formula, the step-by-step math and a table, so every number can be checked by hand.
Room sizing follows the lumen method, which the Illuminating Engineering Society defines as the link between lamps, room features and the average light level on the work plane. Brightness targets come from IES foot-candle guidance, and unit conversions use the NIST SI conversion factors.
The Lumen Method Formula
Lamp lumens equal the target light level times the floor area, divided by the share of light that survives losses. A foot-candle is one lumen per square foot, and a lux is one lumen per square meter, so the units cancel cleanly.
$$\Phi = \frac{E \times A}{LLF \times CU}$$
Here Φ is lamp lumens, E is the target illuminance in fc or lux, and A is floor area in ft² or m². LLF is the light loss factor and CU is the coefficient of utilization, both entered as percentages in the Target & Losses panel.
The Light Level mode runs the same formula in reverse. It takes the lumens you own and returns the average light on the work plane, then compares it with the IES value for the room you picked.
$$E = \frac{\Phi \times LLF \times CU}{A}$$
Light Loss Factor and CU
LLF covers lamp aging and dirt on fixtures. The default 80% means the room is sized so it still meets its target after output drops by a fifth, which is why a 12 × 12 ft living room needs 2,700 lamp lumens rather than the bare 2,160.
CU is the share of lamp lumens that actually reach the work plane after fixtures and walls absorb part of it. The tool loads CU at 100% so the answer matches the simple lumens = lux × area rule. Dark walls, shaded fixtures and tall narrow rooms lower CU, so enter the value from your fixture’s CU table when you have it.
Room Cavity Ratio
The fourth card in Room mode reports the room cavity ratio, the number you need to read a fixture’s CU table. It uses the ceiling height from the Target & Losses panel minus the 30 in (2.5 ft) work plane, which is where IES measures the light level.
$$RCR = \frac{5 \times h_{rc} \times (L + W)}{L \times W}$$
A 12 × 12 ft room with an 8 ft ceiling has a 5.5 ft cavity and an RCR of 4.58. Lower ratios mean wide, low rooms where more light reaches the floor, while higher ratios mean narrow or tall rooms where walls soak up more of it.
Lumens for Common Room Sizes
Most people ask about a specific room, such as a 12×12 bedroom, a 100 sq ft room or a 200 sq ft room. The table below runs the Lumen Calculator default settings for those sizes, with LLF 80% and CU 100%, across the IES ranges for each room type.
| Room size | Living room or bedroom (10–20 fc) | Kitchen or dining (30–40 fc) | Bathroom or home office (20–50 fc) |
|---|---|---|---|
| 100 sq ft (10 × 10 ft) | 1,250–2,500 lm | 3,750–5,000 lm | 2,500–6,250 lm |
| 144 sq ft (12 × 12 ft) | 1,800–3,600 lm | 5,400–7,200 lm | 3,600–9,000 lm |
| 200 sq ft | 2,500–5,000 lm | 7,500–10,000 lm | 5,000–12,500 lm |
| 250 sq ft | 3,125–6,250 lm | 9,375–12,500 lm | 6,250–15,625 lm |
For a 12×12 room used as a living room or bedroom, the tool picks the 15 fc midpoint and returns 2,700 lamp lumens. Four 800 lm bulbs give 3,200 lm, or 119% of the need, and the plan places them on a 2 × 2 grid at 6 ft centers, 3 ft in from each wall.
Those four bulbs draw about 35.6 W at the default 90 lm/W, or about 8.9 W each. Each one meets the 60 W class on old incandescent bulbs, so the same light once took four 60 W lamps, 240 W in total.
Lumens per Square Foot by Room
A lumens per square meter calculator and a lumens per square foot figure are the same idea at two scales. Divide the foot-candle target by LLF and you get lamp lumens per square foot, and the lux target divided by LLF gives lamp lumens per square meter. Card 1 in Room mode shows both for your exact inputs.
Home Rooms
Home targets follow the IES residential levels in Penn State’s EGEE 102 lighting table, which the tool’s presets are built on. Lamp lumens below include the 80% light loss factor.
| Room or task | Target (fc) | Target (lux) | Lamp lm per sq ft | Lamp lm per m² |
|---|---|---|---|---|
| Living room or bedroom | 10–20 | 108–215 | 12.5–25 | 135–269 |
| Kitchen, general | 30–40 | 323–431 | 37.5–50 | 404–538 |
| Kitchen task (stove, sink) | 50–100 | 538–1,076 | 62.5–125 | 673–1,345 |
| Dining room | 30–40 | 323–431 | 37.5–50 | 404–538 |
| Bathroom | 20–50 | 215–538 | 25–62.5 | 269–673 |
| Home office or reading | 20–50 | 215–538 | 25–62.5 | 269–673 |
| Hallway or entry | 5–20 | 54–215 | 6.25–25 | 67–269 |
| Garage, general | 30 | 323 | 37.5 | 404 |
| Garage workbench or shop | 100 | 1,076 | 125 | 1,345 |
Residential levels have no published average, so the tool aims at the middle of each range and the step list labels it as the midpoint. Pick the low end for rooms used by young people with good eyesight, and the high end for older eyes or close work, then type that value into Target Illuminance.
Offices, Schools and Stores
Commercial spaces use the IES 10th Edition averages from Orion Lighting’s IES guideline brochure, and the tool loads the average as its default target. These are lower than many older charts, with 40 fc at an office desk where older tables list 50–100 fc.
| Space | IES average (fc) | IES range (fc) | Average (lux) | Lamp lm per sq ft at average |
|---|---|---|---|---|
| Open or private office (desk) | 40 | 30–50 | 431 | 50 |
| Conference room (table) | 30 | 15–60 | 323 | 37.5 |
| Classroom | 40 | 30–50 | 431 | 50 |
| General retail floor | 50 | 25–100 | 538 | 62.5 |
| Storage, bulky items | 10 | 5–20 | 108 | 12.5 |
| Storage, small labels | 30 | 15–60 | 323 | 37.5 |
| Corridor or stairs | 5 | 2.5–10 | 54 | 6.25 |
| Lunch or break room | 15 | 5–20 | 161 | 18.75 |
The IES range reflects the age of the people using the space, with the low value for mostly younger users and the high value for users over 65. Use the average for a typical office or school, and move up the range only when the users or the task call for it.
Lux to Lumens Conversion
Lux measures light landing on a surface, while lumens measure light leaving a source. You can convert lux to lumens only when you know the area the light covers, and the conversion is exact only when every lumen lands evenly on that area.
$$\Phi = E_{lux} \times A_{m^2}$$
So 400 lux over 1 m² takes 400 lm, and 500 lux over a 10 m² room takes 5,000 lm before losses. Going the other way, 3,000 lumens spread over 10 m² gives 300 lux, or 150 lux over 20 m². The Lumen Calculator’s Light Level mode does this for any room, and setting LLF and CU to 100% gives the pure conversion.
| Light level | Foot-candles | Lumens on 1 m² | Lumens on 10 m² | Comparable IES use |
|---|---|---|---|---|
| 1 lux | 0.093 | 1 | 10 | Below any indoor target |
| 20 lux | 1.86 | 20 | 200 | Under the 5 fc corridor average |
| 50 lux | 4.65 | 50 | 500 | Corridor or stairs |
| 100 lux | 9.29 | 100 | 1,000 | Low end of living room |
| 200 lux | 18.6 | 200 | 2,000 | High end of living room |
| 400 lux | 37.2 | 400 | 4,000 | Kitchen or office desk |
| 500 lux | 46.5 | 500 | 5,000 | Retail floor |
| 1,000 lux | 92.9 | 1,000 | 10,000 | Fine bench work |
A 5,000 lux reading and a 5,000 lumen bulb are not the same thing. A 5,000 lm source only produces 5,000 lux if all of its light lands on a single square meter, which is the kind of level a focused work light gives on a small spot.
Lumens to Watts for LED Lights
Watts measure power, not brightness. An LED’s watts equal its lumens divided by its efficacy in lumens per watt, which is the lm/W figure or the lumens and watts printed on the bulb box.
$$P = \frac{\Phi}{\eta}$$
At the Lumen Calculator default of 90 lm/W, 200 lumens takes about 2.2 W and 1,000 lumens takes about 11.1 W. The Watts mode also places the result against the familiar bulb classes, which a NYSERDA consumer lighting guide lists as 450 lm for 40 W, 800 lm for 60 W, 1,100 lm for 75 W and 1,600 lm for 100 W.
| Lumens | LED watts at 90 lm/W | LED watts at 120 lm/W | Old bulb class it meets |
|---|---|---|---|
| 200 lm | 2.2 W | 1.7 W | Below 40 W |
| 450 lm | 5.0 W | 3.8 W | 40 W |
| 800 lm | 8.9 W | 6.7 W | 60 W |
| 900 lm | 10.0 W | 7.5 W | 60 W |
| 1,000 lm | 11.1 W | 8.3 W | 60 W |
| 1,100 lm | 12.2 W | 9.2 W | 75 W |
| 1,600 lm | 17.8 W | 13.3 W | 100 W |
| 3,000 lm | 33.3 W | 25.0 W | Above 100 W |
| 5,000 lm | 55.6 W | 41.7 W | Above 100 W |
| 10,000 lm | 111 W | 83.3 W | Above 100 W |
For a single bulb, the tool reads the old wattage off a line drawn between those four points, so 1,000 lm maps to 70 W. A 900 lumen LED is a 60 W replacement with some light to spare, since it clears the 800 lm class but falls short of the 1,100 lm needed for 75 W. Switch the Convert field to Watts to Lumens to go the other way, for example 10 W at 90 lm/W gives 900 lm.
The last card in Watts mode gives the current the LED draws on a 120 V circuit and on 12 V DC, plus its energy use at 3 hours a day. That makes it a lumen calculator for LED lights on 12 V strips or solar setups as well as household bulbs.
How Bright Is a Lumen Count?
A lumen count alone does not say how bright a room will look, because the same light spread over a bigger floor gives a lower level. Run any count through the Lumen Calculator and you get the full picture, but the table shows how much floor each lumen count can light to common targets, with the 80% light loss factor applied.
| Lamp lumens | At 10 fc (bedroom low end) | At 15 fc (living room) | At 35 fc (kitchen) | At 100 fc (workbench) |
|---|---|---|---|---|
| 30 lm | 2.4 sq ft | 1.6 sq ft | 0.7 sq ft | 0.24 sq ft |
| 40 lm | 3.2 sq ft | 2.1 sq ft | 0.9 sq ft | 0.32 sq ft |
| 200 lm | 16 sq ft | 11 sq ft | 4.6 sq ft | 1.6 sq ft |
| 1,000 lm | 80 sq ft | 53 sq ft | 23 sq ft | 8 sq ft |
| 2,000 lm | 160 sq ft | 107 sq ft | 46 sq ft | 16 sq ft |
| 3,000 lm | 240 sq ft | 160 sq ft | 69 sq ft | 24 sq ft |
| 4,000 lm | 320 sq ft | 213 sq ft | 91 sq ft | 32 sq ft |
| 5,000 lm | 400 sq ft | 267 sq ft | 114 sq ft | 40 sq ft |
| 10,000 lm | 800 sq ft | 533 sq ft | 229 sq ft | 80 sq ft |
| 14,000 lm | 1,120 sq ft | 747 sq ft | 320 sq ft | 112 sq ft |
| 80,000 lm | 6,400 sq ft | 4,267 sq ft | 1,829 sq ft | 640 sq ft |
A 30 or 40 lumen light is a marker or night light, since it only brings about a square foot or two up to living room level. A 200 lumen LED is a small task light that can light a desk or a book page well, but it cannot light a room on its own.
Can 1,000 lumens light a room? It can light a small one, about 53 sq ft at living room level or 80 sq ft at the 10 fc low end. In a full 12 × 12 ft room, 1,000 lm gives about 5.6 fc, close to hallway level and below what a bedroom needs.
3,000 lumens fits a 12 × 12 ft living room or bedroom, where it lands at about 16.7 fc. 4,000 lumens covers a living area of about 213 sq ft or a kitchen of about 91 sq ft, so whether it is enough depends on the room more than the number.
5,000 lumens is bright for a bedroom but right for a kitchen of about 114 sq ft, and 10,000 lumens in a 12 × 12 ft room gives about 55.6 fc, close to four times the living room target. Counts like 14,000 or 80,000 lumens are shop, warehouse or outdoor flood levels, where 80,000 lm can light about 640 sq ft of workbench area.
How Far Lumens Shine
The Lumen Calculator’s Beam Throw mode answers questions like how far 7,000 lumens will shine. Lumens alone cannot answer it, because a tight beam packs the same light into a smaller cone and sends it much farther than a wide flood.
The tool first finds the solid angle of the beam cone from the beam angle θ, then divides the lumens by that angle to get the peak intensity I in candela, the figure that sets how far the beam reaches.
$$\Omega = 2\pi\left(1 – \cos\frac{\theta}{2}\right)$$
$$I = \frac{\Phi}{\Omega}$$
Beam distance follows the ANSI/PLATO FL1 flashlight standard, which defines throw as the distance where light falls to 0.25 lux. Pelican describes that level as about the light of a full moon on a clear night.
$$d = \sqrt{\frac{I}{0.25}}$$
| Output | 10° spot | 20° spot | 40° beam | 120° flood |
|---|---|---|---|---|
| 1,000 lm | 409 m | 205 m | 103 m | 36 m |
| 7,000 lm | 1,082 m | 542 m | 272 m | 94 m |
| 14,000 lm | 1,530 m | 766 m | 384 m | 134 m |
| 80,000 lm | 3,658 m | 1,831 m | 919 m | 319 m |
When a flashlight or LED lists candela or millicandela instead of lumens, switch Known Value in Beam mode. A 50,000 cd light with a 20° beam works out to about 4,773 lm in the cone and a 447.2 m throw.
A 7,000 lumen light with a 20° beam reaches about 73,300 cd and throws about 542 m, or about 1,777 ft. At 100 m it still puts about 7.3 lux on the target inside a spot about 35 m wide, and the same 7,000 lumens in a 120° flood reaches only about 94 m.
These figures assume every lumen stays inside the cone. Real lights spill part of their output, so a measured ANSI throw is often shorter, and the candela figure on the box is the better input when the maker lists it. For laser beams, where the cone is far tighter, the Laser Beam Divergence Calculator and the Laser Brightness Calculator handle spread and radiance.
Lumen Calculator for a Shop
A garage workbench or shop needs far more light than a living space, and the Lumen Calculator handles it through two presets. The IES residential table lists 100 fc for a garage workbench and 30 fc for general garage use, so a 20 × 20 ft shop lit for bench work needs 50,000 lamp lumens with LLF 80% and CU 100%.
With 4,500 lm LED shop lights, that shop takes twelve fixtures for 54,000 lm, about 600 W at 90 lm/W. A garage used only for parking and storage needs 15,000 lm at 30 fc, and a real CU near 70% for shelved walls would raise the bench figure to about 71,400 lm.
Lumen, Lux and Watt Basics
Several common questions come down to what each unit means. These answers use the SI definitions and the same math the Lumen Calculator runs, so you can check each one in the calculator.
What Is 1 Lumen Equal To?
One lumen is the light a source of one candela sends into one steradian of solid angle. The BIPM candela definition fixes 683 lumens per watt for green light at 540 THz, so one lumen of that light carries 1/683 W, about 1.46 mW. White light needs more watts per lumen, since part of its spectrum sits where the eye is less sensitive.
How Many Lux Is 1 Lumen?
One lumen spread over 1 m² gives 1 lux, and one lumen over 1 ft² gives one foot-candle, which equals 10.764 lux. The answer always depends on area, so the same lumen gives less lux the wider it spreads.
Is 1 Lux Equal to 1 Watt?
No. Lux is lumens per square meter, a measure weighted by the eye’s sensitivity, while watts measure power. Even for the most efficient green light, 1 lux matches only about 1.46 mW per square meter, and for white LED light the power per lux is higher.
Is 1,500 Lumens Too Bright for a Bedroom?
Not for a typical bedroom. In a 12 × 12 ft bedroom, 1,500 lm gives about 8.3 fc after losses, a little under the 10–20 fc range, and in a 10 × 10 ft room it gives about 12 fc, right inside it. A dimmer lets the same fixture drop low at night.
What Does 4000K Mean on a Bulb?
4000K is a color temperature, not a lumen count, so it says nothing about how bright a bulb is. It describes a neutral white that sits between warm 2700K and daylight-style 5000K bulbs, and the Blackbody Radiation Calculator shows where that color comes from on the blackbody curve.
Is 10,000 Lumens Too Bright?
It depends on the floor it covers. In a 12 × 12 ft room it gives about 55.6 fc, too bright for a bedroom but in the range for close task work, while in a 500 sq ft open room it gives about 16 fc, a normal living level.
More light and lens tools sit in the Optics Calculators hub, including calculators for lens power, refraction, telescope resolution and laser beams, all built on the same sourced formulas.