Recessed Lighting Calculator — Count & Spacing
There are two ways to answer "how many cans?" — the spacing rule, which gives even coverage, and the light level the room's use actually calls for. Good layouts satisfy both. This tool runs each one and tells you which is driving the count.
Lay out the room
Use the lumen figure on the box, not the wattage — LED wattage tells you consumption, not output. A 4-inch trim is typically 600–700 lm, a 6-inch 800–1,100 lm.
Fixtures needed
Spacing
4.0 ft
By light level
12
See the breakdown
Both methods agree at 12 fixtures — a 4 × 3 grid at 4.0 ft spacing delivers 7,800 lumens.
The method, explained in plain English
Half the ceiling height
The spacing rule scales with ceiling height because a higher fixture throws light over a wider area. A 10 ft ceiling wants 5 ft spacing, not 4.
Keep off the walls
Set the perimeter row half a spacing in — 2 ft on an 8 ft ceiling. Too close and you get scallops on the wall and a dim middle.
Lumens, not watts
LED wattage says nothing consistent about output. Two 12 W trims can differ by 300 lumens. Read the lumen figure off the box.
General light isn't task light
A perfect ceiling grid still leaves a kitchen counter in your own shadow. Under-cabinet and bench lighting are separate line items.
Worked examples
The same 16 × 12 ft room in three different uses — and one with a taller ceiling.
Kitchen, 8 ft ceiling — both methods agree
The defaults above. 192 ft², 40 fc target, 650 lm trims.
light level: 192 × 40 = 7,680 lm ÷ 650 = 11.8 → 12 fixtures
12 cans, 4 ft apart, 2 ft off the walls
Result: the ideal case — even spacing and the right light level are the same answer. Add under-cabinet lighting separately for the counter.
Same room as a living room — spacing governs
Switch the room use to 20 fc; nothing else changes.
light level: 192 × 20 = 3,840 lm ÷ 650 = 5.9 → 6 fixtures
take the larger → 12 cans on a dimmer
Result: keep the even grid and dim it. Six cans would hit the target light level but leave visible dark patches between them.
Kitchen with a 10 ft ceiling — light level governs
Higher ceiling, so wider spacing and fewer grid positions.
light level: 192 × 40 = 7,680 lm ÷ 650 = 11.8 → 12 fixtures
take the larger → 12 cans, or 6 brighter ones
Result: a taller ceiling needs more output, not fewer fixtures. Either tighten the grid to 12 or specify 1,300 lm trims and keep 6.
Target light levels by room
Fixture counts shown for a 192 ft² room using 650 lumen trims — the reference case above. These are general-illumination targets; task lighting is additional.
| Room | Footcandles | Lumens needed | Fixtures |
|---|---|---|---|
| Hallway, closet | 10 fc | 1,920 lm | 3 |
| Living room, bedroom | 20 fc | 3,840 lm | 6 |
| Dining room | 25 fc | 4,800 lm | 8 |
| Bathroom | 30 fc | 5,760 lm | 9 |
| Kitchen, office | 40 fc | 7,680 lm | 12 |
| Workshop, garage | 50 fc | 9,600 lm | 15 |
Sources & standards: footcandle targets follow general Illuminating Engineering Society practice for residential interiors and are planning figures rather than a code requirement — lighting levels are not mandated by the NEC for dwellings. Fixture installation is governed by NEC (NFPA 70) 2023 Article 410, with 410.116 covering clearance and insulation contact — a non-IC-rated fixture must not be covered by thermal insulation. The spacing convention of half the ceiling height is trade practice, not a standard. Local amendments and the AHJ have final say.
Frequently asked questions
Common questions about recessed lighting count, spacing, and layout.
How many recessed lights do I need?
Two calculations, and you take the larger. The spacing rule puts fixtures roughly ceiling height ÷ 2 apart — 4 ft on an 8 ft ceiling — which on a 16 × 12 ft room gives a 4 × 3 grid, or 12 cans. The light-level check multiplies area by target footcandles and divides by lumens per fixture: 192 ft² × 40 fc = 7,680 lm ÷ 650 lm = 12 fixtures. When both agree, as here, the layout is straightforward.
How far apart should recessed lights be?
Take half the ceiling height as the spacing between fixtures, and half of that again as the distance from the wall. On an 8 ft ceiling that is 4 ft apart and 2 ft off the wall; on a 10 ft ceiling, 5 ft apart and 2.5 ft off. Setting the perimeter row too close to the wall is the most common layout error — it puts scallops on the wall and leaves the middle of the room dim.
How many footcandles does a room need?
It depends on the task. Roughly: hallways and closets 10, living and bedrooms 20, bathrooms 30, and kitchens, offices, and workshops 40. These are general-illumination targets — a kitchen still wants separate under-cabinet lighting for the counter, and a workshop wants task lighting at the bench regardless of how good the ceiling grid is.
How many lumens is a recessed light?
A common 4-inch LED trim delivers around 600–700 lumens and a 6-inch around 800–1,100. Use the figure on the box rather than the wattage — LED wattage tells you consumption, not output, and it varies widely between products. Note the trim's beam angle too: a narrow spot puts the same lumens over a much smaller area than a wide flood.
Can I put recessed lights in contact with insulation?
Only if they are rated for it. A fixture marked IC-rated may be covered by insulation; a non-IC fixture requires clearance — typically 3 inches — and covering it is a genuine fire hazard. In an insulated ceiling you also want an airtight (AT) rating to stop conditioned air leaking into the attic. Modern LED canless fixtures are usually IC-rated and airtight, which is much of their appeal.
How many recessed lights on one circuit?
Far more than you would expect with LEDs. A 15-amp, 120-volt circuit at the 80% continuous limit gives 1,440 VA of usable capacity; at 12 W per LED trim that is over a hundred fixtures, so the practical limit is the switch and dimmer rating rather than the circuit. Confirm the count against the circuit with the Receptacle & Circuit Calculator, and check the dimmer is rated for the total load and for LED drivers.
Should recessed lights be centred on the room or on the furniture?
Centre the grid on the room so the spacing reads evenly, then adjust individual fixtures for what is below them. Common adjustments: pull the row over a kitchen island so it lights the work surface rather than the walkway, and keep cans out of the arc of a door swing or a cabinet front where they would only light the doors.
Layout set? Quote the lighting in seconds.
Lighting jobs are quantity-heavy — trims, drivers, boxes, switches, dimmers, and labor per fixture. TradesQuote turns the layout into a detailed line-item estimate with quantities and totals, validated by a built-in quality control agent.
AI line-item estimates
Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
Shareable & signable
Clients review, accept, and sign from a public link.
No credit card required · 14-day free trial · Cancel anytime