# How much recessed lighting do I need?

Computes how many recessed (can) lights a rectangular room needs on an even grid, the spacing between them, the distance from the walls, and the lumens per square foot.

- Page: https://www.acalculator.org/construction/recessed-lighting-calculator
- JSON spec: https://www.acalculator.org/construction/recessed-lighting-calculator.json
- Version: 0245b0f14e89

## Default answer

Example with the default inputs (Room length 15 ft, Room width 12 ft, Ceiling height 8 ft): You need 12 recessed lights: 4 along the length and 3 along the width.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| l | Room length | The length of the room, wall to wall. |
| w | Room width | The width of the room, wall to wall. |
| h | Ceiling height | The height of the ceiling above the floor. |
| s | Spacing between lights | The largest gap you want between lights. Leave empty to use half the ceiling height. |
| lm | Lumens per light | The light output of one fixture, in lumens, from its box. Leave empty to skip brightness. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| count | Lights | Lights along the length × lights along the width. |
| along | Lights along the length | Room length ÷ spacing, rounded up. |
| across | Lights along the width | Room width ÷ spacing, rounded up. |
| gapL | Gap along the length (ft) | Room length ÷ lights along the length, in feet. |
| gapW | Gap along the width (ft) | Room width ÷ lights along the width, in feet. |
| wallL | From the end walls (ft) | Half the gap along the length, in feet. |
| wallW | From the side walls (ft) | Half the gap along the width, in feet. |
| gapLm | Gap along the length (m) | The gap along the length in metres. |
| gapWm | Gap along the width (m) | The gap along the width in metres. |
| perFt2 | Lumens per ft² | Lights × lumens per light ÷ the floor area in square feet. |
| total | Total lumens | Lights × lumens per light. |

## Method

Spacing = ceiling height ÷ 2 (or the spacing you type); lights along each wall = wall length ÷ spacing, rounded up; lights = along × across; gap = wall length ÷ lights on it; distance from the wall = gap ÷ 2.

## Assumptions

- Lights at most half the ceiling height apart (Amico and Lumary: an 8 ft ceiling gives 4 ft).
- An even grid, with the outer lights half a gap from the walls (Amico).
- Brightness is the fixtures’ total lumens over the floor area; Lumary uses about 10 to 20 lumens per ft² for a living room or bedroom.

## Worked examples

1. l = 4.572, w = 3.6576, h = 2.4384 gives along = 4, across = 3, count = 12, gapL = 3.75, gapW = 4, wallL = 1.875, wallW = 2. Source: Amico, Where to Place Recessed Lights (ceiling height ÷ 2; perimeter lights half the spacing from the walls), https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room.
2. l = 6.096, w = 4.2672, h = 3.048, lm = 800 gives along = 4, across = 3, count = 12, gapW = 4.666667, total = 9,600, perFt2 = 34.285714. Source: Lumary, What is the recommended spacing between each recessed light? (roughly half the ceiling height; a 10 ft ceiling about 5 ft apart), https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light.
3. l = 4, w = 3, h = 2.4 gives along = 4, across = 3, count = 12, gapLm = 1, gapWm = 1. Source: Amico, Where to Place Recessed Lights (ceiling height ÷ 2), https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room.
4. l = 4.572, w = 3.6576, h = 2.4384, s = 1.8288 gives along = 3, across = 2, count = 6, gapL = 5, gapW = 6. Source: Lumary, recommended spacing between recessed lights (4 to 6 ft for typical downlights), https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light.

## FAQ

### How far apart should recessed lights be?

A common rule from lighting makers is half the ceiling height: 4 ft apart under an 8 ft ceiling, 4.5 ft under 9 ft, and 5 ft under 10 ft. Lumary says most rooms end up with lights 4 to 6 ft apart.

### How far from the wall should recessed lights be?

About half the gap between the lights, so the light from the outer row meets the light from the next row. Under an 8 ft ceiling that is about 2 ft from the wall.

### How many recessed lights do I need for a 12 × 15 room?

With an 8 ft ceiling the lights go at most 4 ft apart. 15 ÷ 4 = 3.75, so 4 lights along the 15 ft wall, and 12 ÷ 4 = 3 along the 12 ft wall: 12 lights in all, 3.75 ft and 4 ft apart.

### How many lumens do I need in a room?

Multiply the floor area by the lumens per square foot the room needs. Lumary’s example is 1,000 to 2,000 lumens for a 100 ft² living room or bedroom, so 10 to 20 lumens per square foot. Kitchens and work areas need more.

### Why round the number of lights up?

Rounding down would put the lights further apart than the spacing you chose and leave dark patches between them. The calculator rounds up, then spreads the lights evenly, so the real gap is never wider than your spacing.

### Can I use a different spacing?

Yes. Type your own spacing, for example from the fixture maker’s spacing guide, and the calculator uses it in place of half the ceiling height.

## Sources

- Amico, Where to Place Recessed Lights: The Rule of Thumb for Every Room (ceiling height ÷ 2: 8 ft ceiling 4 ft apart, 9 ft 4.5 ft, 10 ft 5 ft; perimeter fixtures half the spacing from the walls). https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room (retrieved 2026-10-02)
- Lumary, What is the recommended spacing between each recessed light? (space each light at roughly half the ceiling height; 4–6 ft for typical downlights; 1,000–2,000 lumens for a 100 ft² living room or bedroom). https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light (retrieved 2026-10-02)
- NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement: 1 ft = 0.3048 m; 1 ft = 12 in. https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-01)