How many lumens do I need? Lighting worked out for your room
Plan on about 200–400 lumens per square metre of floor for a living room with light walls: that gives the 100–200 lux UK lighting guidance suggests, once you allow for the light that walls and shades take in. An 18 m² living room needs about 3,600–7,200 lm in all: five to nine 806 lm (60 W) bulbs, spread over the ceiling and lamps. A kitchen needs about 325–650 lm per m², a bedroom 110–220. Space downlights about half the ceiling height apart: 1.2 m under a 2.4 m ceiling, 60 cm from the walls.
Type your room's length, width and ceiling height, and choose the room and the wall colour. The calculator gives the lumens the room needs, how to split them between the ceiling, lamps and task lights, how many bulbs that is, where downlights go, and which colour of white to buy.
The formula
Two words first. Lumens (lm) are the light a bulb gives out: the number on the box. Lux is the light that arrives on a surface, such as the floor or a table: one lumen spread over one square metre.
Bulb lumens = lux × floor area ÷ utilisation factor.
The utilisation factor is the share of the bulbs' light that reaches the floor and tables. The rest lands on the walls and ceiling, or stays in the shade.
Lighting engineers read the factor from tables, by the room's shape and how pale its surfaces are. For homes we use a simple fit to those tables: 0.3 + 0.15 × the room index, kept between 0.35 and 0.65, and 0.1 lower with dark walls. The room index is length × width ÷ (height × (length + width)), with the height measured from about desk height, 80 cm, to the ceiling. Small rooms and high ceilings get a lower factor, because more of the light hits the walls.
For a 4.5 × 4 m living room with a 2.4 m ceiling and light walls: the floor is 18 m², the room index is 18 ÷ (1.6 × 8.5) = 1.32, and the factor is 0.3 + 0.15 × 1.32 = 0.50. For 100–200 lux, the bulbs need 100–200 × 18 ÷ 0.5 = 3,600–7,200 lm.
Many online calculators multiply lux by area and stop there. That assumes every lumen lands on the floor, so it suggests about half the light a room needs.
Lumens for each room
For a room with light walls and a 2.4 m ceiling. Dark walls need about a quarter more.
| Room | Lux | Lumens per m² | Example room | Lumens in all | 806 lm bulbs | Colour |
|---|---|---|---|---|---|---|
| Living room | 100–200 | 200–400 | 4.5 × 4 m | 3,600–7,200 | 5–9 | 2700–3000 K |
| Small living room | 100–200 | 225–445 | 3.5 × 3 m | 2,350–4,650 | 3–6 | 2700–3000 K |
| Bedroom | 50–100 | 110–225 | 3.5 × 3 m | 1,150–2,350 | 2–3 | 2700–3000 K |
| Kitchen | 150–300 | 325–650 | 4 × 3 m | 3,900–7,800 | 5–10 | 3500–4500 K |
| Bathroom | 100–150 | 250–370 | 2.5 × 2 m | 1,250–1,850 | 2–3 | 3500–4500 K |
| Home office | 250–300 | 585–700 | 3 × 2.5 m | 4,400–5,250 | 6–7 | 4000–5000 K |
No UK standard sets light levels for private homes. The figures above come from guidance written for other buildings with rooms like ours: SLL's guide for communal residential buildings (lounges, kitchens, bathrooms and bedrooms in flats and care homes), the 1994 CIBSE Code's hotel rooms, and CIBSE's office figures for a home office. For tasks, the same guidance asks for more light where you work: 500 lux at a desk (CIBSE's office figure) and 200 lux on a book (SLL LG9). Kitchens in schools are lit to 500 lux, a fair target for a worktop.
Split the light into layers
A rule designers use is to light a room from at least two or three sources, at two or more heights, rather than from one ceiling light. Low lamps give the pooled, side-lit light that many people associate with a relaxed evening; a ceiling light alone lights the floor and the tops of heads.
| Room | Ceiling | Lamps | Task | Task light |
|---|---|---|---|---|
| Living room | 30% | 50% | 20% | Reading lamps by the seats |
| Bedroom | 40% | 40% | 20% | Bedside reading lights |
| Kitchen | 60% | – | 40% | Lights under the wall cupboards |
| Bathroom | 70% | – | 30% | Lights beside the mirror |
| Home office | 50% | 20% | 30% | A desk lamp |
For the 18 m² living room, that is about 1,100–2,150 lm from the ceiling, 1,800–3,600 lm from lamps and 700–1,450 lm from reading lamps. Two table lamps and a floor lamp with 806 lm bulbs give about 2,400 lm, inside the lamp range.
How many downlights
A rule installers use is to space downlights about half the ceiling height apart, and half that again from the walls, so the pools of light meet evenly. The calculator rounds to a whole grid, so the gaps fit your room exactly.
| Ceiling height | Apart | From the wall | 4.5 × 4 m room | 2.5 × 2 m bathroom |
|---|---|---|---|---|
| 2.4 m (7 ft 10 in) | About 1.2 m | About 60 cm | 12 (4 × 3) | 4 (2 × 2) |
| 2.7 m (8 ft 10 in) | About 1.35 m | About 68 cm | 9 (3 × 3) | 2 (2 × 1) |
| 3.0 m (9 ft 10 in) | About 1.5 m | About 75 cm | 9 (3 × 3) | 2 (2 × 1) |
In a living room, 12 downlights sharing 1,100–2,150 lm need only about 90–180 lm each, much less than most GU10 bulbs give. Choose dimmable ones, or use fewer downlights and more lamps.
Lumens and watts
LED boxes still say what old bulb they replace. The figures behind those claims are set by law:
| Says on the box | At least |
|---|---|
| 40 W equivalent | 470 lm |
| 60 W equivalent | 806 lm |
| 75 W equivalent | 1,055 lm |
| 100 W equivalent | 1,521 lm |
The colour of the light is a separate number on the box, in kelvin. Warm white is 2700–3000 K, cool white about 4000 K. Our guide to warm white vs cool white says which one shops suggest for each room, and why it is a matter of taste.
How to measure
- Measure the room's length and width at floor level, wall to wall. For an L-shaped room, split it into two rectangles and add the results.
- Measure the ceiling height from the floor. Under a sloping ceiling, use the average height.
- Call the walls dark if they are a mid or deep colour, or panelled in wood. White, cream and pale greys count as light.
- Count the lumens you already have: read each bulb, or look up its model. Then buy the difference.
Five mistakes
- One ceiling light for the whole room. It puts the light on the floor and leaves the corners and faces dim. Add lamps at sitting height.
- Buying by watts. An LED's watts say what it uses, not how bright it is. Buy by lumens.
- Forgetting dark walls. A deep green room needs about a quarter more light than the same room in white.
- Downlights too close to the walls. They light the wall in bright scallops and leave the middle of the room dimmer. About half the spacing from the wall looks even.
- Mixing whites. A 2700 K lamp beside a 4000 K ceiling light looks patchy. Lighting shops advise one colour temperature per room.
Where sources disagree
| Question | What sources say | We use |
|---|---|---|
| Living room | SLL LG9 (2013): lounge 100–200 lux, 200 lux for reading, TV lounge 50. | 100–200 lux |
| Bedroom | SLL LG9: 100 lux, 250 at a desk. 1994 CIBSE Code, hotel bedrooms: 50–100 lux. | 50–100 lux |
| Kitchen | SLL LG9: 200 lux. 1994 CIBSE Code: 150–300 lux. Kitchens in schools: 500 lux. | 150–300 lux, 500 on the worktop |
| Bulb lumens | Many online calculators: lux × area. The lumen method: lux × area ÷ utilisation factor. | The lumen method, with our simple factor |
| Downlight spacing | Philips Hue: half the ceiling height. Some UK shops: a third. Some US sites: up to the full height. | Half the ceiling height |
The lux figures are for averages across a room. Light levels in a home are a matter of taste and task, so use the range, and dimmers, rather than one exact number. Making a small room feel brighter? See how to make a room look bigger and how to make a room cosy. Dressing the window too? The curtain size calculator sizes the pole and the pair.
See where your lamps go before you buy them
Snuug, the iPhone room app, rebuilds your room in 3D from one slow walk round it, to within about 3% of its real size in our tests of ten homes.
Place a floor lamp by the sofa and a pair of lamps on the sideboard, try them in each corner, and see where they go in your own room before you buy them. Paste a shop link and see the lamp at its real size, and move every piece in 5 cm steps. Members get a Room Analysis that points out where the light falls short, with a plan that starts with the free fixes. Our team checks every room by hand, and your first room is free.
Questions
How many lumens do I need for a living room?
About 200–400 lm per square metre of floor with light walls, for 100–200 lux. A 4 × 4.5 m living room needs about 3,600–7,200 lm in all, from the ceiling light and lamps together. With dark walls, add about a quarter. Put it on dimmers: you will rarely want all of it at once.
How many lumens per square metre do I need?
It depends on the room. With light walls and a 2.4 m ceiling: a bedroom about 110–220 lm per m², a living room 200–400, a bathroom 250–370, a kitchen 325–650 and a home office about 600–700. Small rooms need more per m², because more of the light lands on the walls.
How many downlights do I need?
Space them about half the ceiling height apart, and half that from the walls. Under a 2.4 m ceiling that is about 1.2 m apart and 60 cm from the walls: 12 downlights (4 × 3) in a 4.5 × 4 m room, or 4 in a 2.5 × 2 m bathroom.
Is lux the same as lumens?
No. Lumens are the light a bulb gives out. Lux is the light that arrives on a surface: one lumen spread over one square metre. Because walls, ceilings and shades take in some light, a room needs more bulb lumens than lux × floor area.
How many lumens is a 60 W bulb?
An LED bulb sold as a 60 W equivalent gives at least 806 lumens. 40 W means 470 lm, 75 W means 1055 lm and 100 W means 1521 lm, by the EU's equivalence table that UK packs still use.
Should I use warm white or cool white?
Lighting shops usually suggest warm white, 2700–3000 K, for living rooms and bedrooms, and neutral to cool white, 3500–4500 K, for kitchens and bathrooms. It is a convention and a matter of taste. Our guide to warm white vs cool white has the detail.
Editorial notes
Written by the Snuug team and checked on 1 November 2026. A number with no source beside it is a designers' rule of thumb, not a study.
- Spear Lighting, Technical section: residential lux levels from SLL LG9 (2013), BS EN 12464-1 and HSG38, and office lux levels (catalogue pages 388–391, PDF of 18 Sep 2020), read 31 Oct 2026
- CIBSE, SLL LG9 Lighting for communal residential buildings (2022 edition, paywalled: we have not read it), checked 31 Oct 2026
- CIBSE Code for Interior Lighting (1994), hotel table as reproduced on SlideShare (bedroom 50–100, kitchen 150–300 lux), checked 31 Oct 2026
- electricaltechnology.org (2017), Lighting design calculation in a building, step by step (the lumen method; utilisation factor 0.66 at room index 1.8 with light surfaces), checked 31 Oct 2026
- Commission Regulation (EU) 2019/2020, equivalence claims for non-directional light sources (470 lm = 40 W, 806 lm = 60 W, 1055 lm = 75 W, 1521 lm = 100 W)
- Philips Hue, How far should recessed lights be from the wall? (ceiling height ÷ 2 apart; 50–60 cm from the wall at 2.4 m), read 31 Oct 2026
- BLT Direct (7 May 2026), What is the difference between warm white, cool white and daylight LEDs?
- Emily Henderson, 19 lighting combos and rules (at least 2–3 light sources, at 2 or more heights). The page refused our fetch; figures from search summaries, checked 15 Oct 2026
Use this from an AI assistant
This answer as JSON, or as one paragraph with format=text: https://snuug.app/api/v1/tools/lighting
MCP server: https://snuug.app/mcp · OpenAPI · llms.txt. Every rule cites its source.