Recessed Lighting Calculator
How many recessed lights a room needs, how far apart and how far off the walls, with sourced footcandle targets by room and the lumens each fixture has to put out.
Recessed Lighting Calculator: with the default inputs, recessed lights is 12.
Sets the light-level target. The table under the results shows every source and what each one says.
Used only when the room is set to “Something else”. One footcandle is one lumen per square foot on the lit surface.
Floor to ceiling. Half of it is the spacing rule of thumb.
Read it off the box, not the wattage. Halo's residential downlights run 600–1,200 lm; Kichler suggests 1,000 lm where the ceiling is over 10 ft.
The layout the spacing rule gives — rows × columns, rounded up.
- Laid out as
- 3 rows of 4
- Spacing to use
- 4 ftHalf the ceiling height, capped at 6 ft and at the spacing criterion.
- Actual spacing along the length
- 4 ft
- Actual spacing across the width
- 4 ft
- Widest spacing that still looks even
- 9.6 ftSpacing criterion × the mounting height above the work plane.
- Light level target
- 35Footcandles — see the sources table.
- Total lumens the room needs
- 6,720
- Lumens each fixture has to put out
- 560Total ÷ the number of lights. Buy fixtures at or above this, or plan on a second layer of light.
- Lumens this layout actually installs
- 9,600
- Light level you would get
- 50With the fixture lumens you entered, at the same derating.
- Floor area
- 192 ft²
Assumptions
- There is no free primary authority for residential footcandle levels: ANSI/IES RP-11-20 and the IES Lighting Handbook are paywalled, the ALA never published a table, and the DOE pages that did are gone. Every figure here comes from the named manufacturer and retailer sources in the table, which disagree by two to three times on some rooms.
- The target used is the median of the midpoints of the cited general-lighting ranges — a rule you can check against the table columns by hand.
- Home office, laundry and garage targets come from a single retailer table and are task-plane figures that assume a desk or bench light as well.
- Lumens × area is the naive lumen method: it assumes every lumen reaches the work plane. It ignores coefficient of utilization and light loss factor, neither of which has a citable residential default, so the derating field is yours to set.
- Spacing is the tightest of three published rules: half the ceiling height, 6 ft, and the fixture's spacing criterion × mounting height.
- The layout is a plain rectangular grid. Real rooms have islands, beams, joists and cabinets, and the electrician will move lights to miss them.
- Light counts round up.
| Room | USAI (IES-attributed) | Bees Lighting | Super Bright LEDs | Used here |
|---|---|---|---|---|
| Kitchen | 15–20 at the floor; 40 on the worktop | 30–40 general, 70–80 at stove and sink | 20–50 general, 50–100 preparing | 35 fc |
| Bathroom | 10–15 circulation; 20–30 at the vanity | 70–80 | 20–50 | 35 fc |
| Living room | 10–15 ambient; 35–50 for reading | 10–20 | 10–20 | 15 fc |
| Bedroom | 6–15 ambient; up to 40 for reading | 10–20 | 20–50 | 15 fc |
| Dining room | 10–15 ambient; 40–50 on the table | 30–40 | 10–20 | 15 fc |
| Hallway or landing | 10–15 | 5–10 | 5–10 | 7.5 fc |
| Home office or study | — | 60–80 | 50–100 (difficult reading and writing) | 72.5 fc |
| Laundry | — | — | 20–100 | 60 fc |
| Garage or workshop | — | — | 20–75 | 47.5 fc |
One footcandle is one lumen per square foot. The figure used here is the median of the midpoints of the general-lighting ranges in the columns — the sources disagree by two to three times on kitchens, bathrooms and dining rooms, and that disagreement is real. ANSI/IES RP-11-20 is the primary document and it is paywalled.
| Ceiling | Spacing (half the height, capped at 6 ft) | Lights in a 192 ft² room this shape |
|---|---|---|
| 7 ft | 3.5 ft | 20 |
| 8 ft | 4 ft | 12 |
| 9 ft | 4.5 ft | 12 |
| 10 ft | 5 ft | 12 |
| 11 ft | 5.5 ft | 12 |
| 12 ft | 6 ft | 9 |
| 14 ft | 6 ft | 9 |
Kichler's rule: divide the ceiling height by two, and never go more than 6 ft apart.
How this is worked out
The formula
Spacing = the smallest of: ceiling height ÷ 2, 6 ft, and spacing criterion × mounting height Mounting height = ceiling height − work plane height Lights along a side = ceil((side − 2 × wall setback) ÷ spacing) + 1 Lights = rows × columns Lumens the room needs = floor area in ft² × footcandle target ÷ derating Lumens per fixture = total ÷ number of lights Footcandles delivered = lights × fixture lumens × derating ÷ floor area
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Room
- Sets the light-level target. The table under the results shows every source and what each one says.Kitchen · Bathroom · Living room · Bedroom · Dining room · Hallway or landing · Home office or study · Laundry · Garage or workshop · Something else — set the target yourself
- Light level target
- Used only when the room is set to “Something else”. One footcandle is one lumen per square foot on the lit surface.from 1 to 200 · defaults to 20
- Room length
- A number.in ft, in, m, cm · 0 or more · defaults to 16
- Room width
- A number.in ft, in, m, cm · 0 or more · defaults to 12
- Ceiling height
- Floor to ceiling. Half of it is the spacing rule of thumb.in ft, in, m, cm · 0 or more · defaults to 8
- Lumens per fixture
- Read it off the box, not the wattage. Halo's residential downlights run 600–1,200 lm; Kichler suggests 1,000 lm where the ceiling is over 10 ft.from 1 to 20000 · defaults to 800
- Distance from the wall(under More options)
- Kichler says no less than 2 ft; Halo's kitchen guide uses 24 in over a worktop and the ALA used to say 30 in. Closer than 2 ft scallops the wall.in in, ft, cm, m · 0 or more · defaults to 24
- Force a spacing(under More options)
- Leave 0 to use the rule: half the ceiling height, capped at 6 ft and at the fixture's spacing criterion.in ft, in, m, cm · from 0 to 40 · defaults to 0
- Spacing criterion of the fixture(under More options)
- From the fixture's spec sheet — Halo's residential downlights are 1.14 to 1.38. Multiply it by the mounting height above the work plane for the widest spacing that still looks even.from 0.1 to 3 · defaults to 1.2
- Height of the work plane(under More options)
- 0 means the floor, which is how the room targets are stated. Use 36 in for a kitchen worktop or 30 in for a desk.in in, ft, cm, m · 0 or more · defaults to 0
- Share of fixture lumens reaching the work plane(under More options)
- 100% is the usual shortcut and it flatters the answer — real rooms lose light to walls, dirt and lamp ageing. Zumtobel's handbook uses a maintenance factor of 0.67 for commercial work, and that is before room geometry.a percentage · from 1 to 100 · defaults to 100
What you get back
- Recessed lightsmain answer
- The layout the spacing rule gives — rows × columns, rounded up.
- Laid out as
- Spacing to use
- Half the ceiling height, capped at 6 ft and at the spacing criterion.
- Actual spacing along the length
- Actual spacing across the width
- Widest spacing that still looks even
- Spacing criterion × the mounting height above the work plane.
- Light level target
- Footcandles — see the sources table.
- Total lumens the room needs
- Lumens each fixture has to put out
- Total ÷ the number of lights. Buy fixtures at or above this, or plan on a second layer of light.
- Lumens this layout actually installs
- Light level you would get
- With the fixture lumens you entered, at the same derating.
- Floor area
What this assumes
- There is no free primary authority for residential footcandle levels: ANSI/IES RP-11-20 and the IES Lighting Handbook are paywalled, the ALA never published a table, and the DOE pages that did are gone. Every figure here comes from the named manufacturer and retailer sources in the table, which disagree by two to three times on some rooms.
- The target used is the median of the midpoints of the cited general-lighting ranges — a rule you can check against the table columns by hand.
- Home office, laundry and garage targets come from a single retailer table and are task-plane figures that assume a desk or bench light as well.
- Lumens × area is the naive lumen method: it assumes every lumen reaches the work plane. It ignores coefficient of utilization and light loss factor, neither of which has a citable residential default, so the derating field is yours to set.
- Spacing is the tightest of three published rules: half the ceiling height, 6 ft, and the fixture's spacing criterion × mounting height.
- The layout is a plain rectangular grid. Real rooms have islands, beams, joists and cabinets, and the electrician will move lights to miss them.
- Light counts round up.
About this calculator
Two different questions get asked as "how many recessed lights do I need", and they have two different answers. How many holes go in the ceiling is a spacing problem — it depends on the ceiling height and the room's shape, and it is what stops the ceiling looking like a runway or a leopard. How bright they have to be is a lumens problem — it depends on the floor area and what the room is for. This page answers both, and the second answer is the one people get wrong: you pick the layout first, then buy fixtures whose output suits it.
Spacing: half the ceiling height
Kichler's own placement guide gives the rule most electricians use — "divide your ceiling height by 2 to give you the space between each light, but don't go more than 6 feet apart" — and "start with downlights no less than 2 feet away from your walls." So an 8 ft ceiling gets lights about 4 ft apart, with the first row 2 ft in. Halo's kitchen guide uses 24 in from the wall over a worktop; the American Lighting Association used to say 30 in. Closer than about 2 ft and you get scalloped arcs down the wall.
Under More options is the spacing criterion, the number your fixture's spec sheet publishes — Eaton describe it as a ratio "usually between 0.5 and 1.5" that you multiply by the mounting height to get the widest spacing that still reads as even. Halo's residential downlights sit at 1.14 to 1.38. The calculator takes whichever of the three limits is tightest.
Brightness: footcandles, and an honest warning about them
A footcandle is one lumen landing on one square foot. Multiply your floor area by the target and you have the lumens the room needs. The awkward part is the target, because there is no free authoritative table of residential light levels. The IES documents that everyone cites — RP-11 and the Lighting Handbook — are paywalled; the American Lighting Association never published one; the Department of Energy pages that used to carry one are gone. What is public is a handful of manufacturer and retailer tables that disagree with each other by two to three times on kitchens, bathrooms and dining rooms.
So rather than quietly pick one, the table under your results prints every figure we could source and names who said it, and the target used is the median of their midpoints. Treat it as a starting point, put the lights on a dimmer, and trust your eyes.
The number this calculator will not fudge
The simple rule — area × footcandles = lumens — assumes every lumen a fixture emits lands on the work plane. None of them do: light is absorbed by walls, lost to dirt on the lens, and lost again as the LED ages. Designers handle this with a coefficient of utilization and a light loss factor, both per-fixture and per-room, and neither with a citable residential default. So the derating field defaults to 100% and tells you it is flattering the answer. Zumtobel's handbook uses a maintenance factor of 0.67 for commercial work, before room geometry.
Reading the results
Recessed lights is the layout. Lumens each fixture has to put out is what to buy — compare it with the 600–1,200 lm Halo's residential downlights deliver. If the warning says your fixtures over- or under-shoot, the fix is usually different fixtures, not different holes.
Frequently asked questions
▸How far apart should recessed lights be?
Divide the ceiling height by two — 4 ft apart on an 8 ft ceiling, 4½ ft on a 9 ft ceiling — and never go more than 6 ft apart, which is Kichler's published rule. Your fixture's spacing criterion, on its spec sheet, sets the true maximum.
▸How far from the wall should the first row be?
About 2 to 2½ ft. Kichler says no less than 2 ft, Halo's kitchen guide uses 24 in over a worktop, and the American Lighting Association used to recommend 30 in. Closer than that and you get scalloped arcs on the wall.
▸How many lumens does a room need?
Floor area in square feet × the footcandle target. A 200 ft² kitchen at 35 fc needs about 7,000 lumens. Be sceptical of any single target though — the public sources disagree by two to three times, which is why this page prints all of them.
▸How many recessed lights for a 12 × 12 room?
On an 8 ft ceiling at 4 ft spacing with a 2 ft setback, that is three rows of three — nine lights. Whether they should be 500 lm or 900 lm each depends on what the room is for, and the calculator works that out separately.
▸Does a 6-inch can put out more light than a 4-inch?
Not any more. Eaton's own lighting people say aperture size no longer predicts output — a 4 in LED downlight can match a 6 in one. Buy by lumens, not by hole size.
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