Strobe Candela Chart — Wall-Mounted, by Room Size
Minimum candela rating for a wall-mounted fire alarm strobe by room size, per NFPA 72 Table 18.5.5.4.1(a) (2022 edition), with the reduced per-strobe ratings when two or four appliances share a room. Room sizes are square; use the longest wall for a rectangular room. Ceiling-mounted strobes and corridors use separate tables — see the related charts. The authority having jurisdiction has the final say on the layout.
Wall-mounted strobe candela by room size
| Max room size | One strobe | Two strobes | Four strobes |
|---|---|---|---|
| 20 × 20 ft | 15 cd | — | — |
| 30 × 30 ft | 30 cd | 15 cd | — |
| 40 × 40 ft | 60 cd | 30 cd | 15 cd |
| 50 × 50 ft | 95 cd | 60 cd | 30 cd |
| 60 × 60 ft | 135 cd | 95 cd | 30 cd |
| 70 × 70 ft | 185 cd | — | 60 cd |
| 80 × 80 ft | 240 cd | — | 60 cd |
| 90 × 90 ft | 305 cd | — | — |
| 100 × 100 ft | 375 cd | — | — |
How to read this chart
Find the room's longest wall, round up to the next listed room size, and read the candela in the column for the number of strobes you're installing. A single strobe is the common case; the two- and four-strobe columns exist because spreading appliances around a room lets each one be a lower — cheaper, lower-current — candela rating while still washing the whole space with light. The lens must sit between 80 in and 96 in above the finished floor (see the mounting heights chart).
This table is for wall mounting. A strobe on the ceiling covers a room differently — use the ceiling strobe candela chart, which factors in ceiling height. Corridors 20 ft wide or less have their own simpler rule on the corridor spacing chart.
Edition and jurisdiction
The candela values are stable across NFPA 72 editions — the notification chapter moved (Chapter 6 before 1999, Chapter 7 through 2007, Chapter 18 since 2010) but the numbers did not. The main change over time was extending the one-strobe column past 70×70 ft. Confirm the edition your jurisdiction enforces, and remember the AHJ can require more coverage than the table minimum, especially in high-ambient or visually obstructed spaces.
Common questions
What candela strobe do I need for a room?
Per NFPA 72 (Table 18.5.5.4.1(a), 2022 edition), size a single wall strobe by the room's longest wall: a 20×20 ft room needs 15 cd, 30×30 ft needs 30 cd, 40×40 ft needs 60 cd, 50×50 ft needs 95 cd, 60×60 ft needs 135 cd, and it climbs to 375 cd at 100×100 ft. Take the next candela step up if the room is between listed sizes, and treat a non-square room by its longest dimension.
Does the strobe have to be centered on the wall?
No, but the table assumes the appliance effectively covers the whole room. If the strobe is not centered, double the distance from the appliance to the farthest wall and use that as the "room size" for the lookup — an off-center strobe covers a smaller effective room than a centered one at the same candela.
How do multiple strobes reduce the candela needed?
Two strobes on opposite walls, or four strobes with one per wall, each cover the room at a lower individual candela than a single strobe would — the two- and four-strobe columns show the reduced per-strobe rating. Rooms 80 ft and larger in any dimension require at least four strobes, and more than two strobes in a room smaller than 55×55 ft must either be at least 55 ft apart or synchronized.
What candela is required in a sleeping room?
Sleeping rooms are sized separately: 110 cd if the strobe is 24 in or more below the ceiling, and 177 cd if it is closer than that to the ceiling. The strobe must also be within 16 ft of the pillow in a room larger than 16×16 ft.
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