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Emergency Lighting Calculator

Calculate emergency lighting units, exit signs, and battery capacity per NFPA 101/IBC.

About this calculator

NFPA 101 (the Life Safety Code) requires emergency egress lighting to provide an initial average of at least 1 foot-candle and a minimum of 0.1 foot-candle at any point along the path of egress, measured at floor level, sustained for a minimum of 90 minutes (1.5 hours) if normal power fails. Emergency Light Units here is driven entirely by Total Floor Area, Total Corridor Length, and Stairwells, using a conservative 600 sq ft of coverage per unit and a 30 ft spacing along corridors — Number of Exits and Battery Duration have zero effect on that unit count, since exit signage and battery sizing are calculated separately. Battery Capacity instead depends on Battery Duration multiplied by total connected wattage, with a 20% safety margin layered on top to account for battery capacity fade over its service life.

Duration Compliant simply checks whether your entered Battery Duration meets the 90-minute code minimum, so setting Battery Duration below 1.5 hours will show a non-compliant result — useful for checking an existing or legacy system against current code rather than only ever modeling a compliant one. This calculator estimates equipment counts from floor plan geometry; it does not replace a photometric point-by-point calculation, which is what code officials and lighting designers actually use to verify the 1 fc average / 0.1 fc minimum / 40:1 uniformity requirements are met in practice.

Inputs

sq ft
ft

Results

Emergency Light Units

28

Exit Signs Required

6

Total Power Draw (watts)310
Battery Capacity (Wh)558
Estimated Equipment Cost$2,370.00
Duration CompliantYes — meets 90-min NFPA 101 minimum

Figures current as of 2026. Source: National Fire Protection Association, NFPA 101, Life Safety Code

How to Use This Calculator
  1. Enter Total Floor Area (sq ft), Total Corridor Length (ft), and Stairwells.
  2. Set Number of Exits and Battery Duration (hours).
  3. Review Emergency Light Units and Exit Signs Required.
  4. Use Total Power Draw (watts) and Battery Capacity (Wh) to inform your decision.

How the result changes with Total Floor Area (sq ft)

Total Floor Area (sq ft)Emergency Light UnitsExit Signs Required
5,000206
7,500246
15,000366
25,000536

What each input means

Total Floor Area (sq ft)
Total floor area requiring emergency illumination.
Total Corridor Length (ft)
Combined length of all egress corridors.
Stairwells
Number of stairwells requiring emergency lighting.
Number of Exits
Number of building exits.
Battery Duration (hours)
Battery backup duration. NFPA 101 code minimum is 1.5 hrs (90 min) — enter a lower value to see how an undersized battery falls short of compliance.

What each result means

Duration Compliant
Whether Battery Duration meets the NFPA 101 90-minute minimum.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    5 parameters
    Total Floor Area (sq ft) = 10000, Total Corridor Length (ft) = 200, Stairwells = 2, Number of Exits = 4, Battery Duration (hours) = 1.5 = 5 input(s) provided
  2. Calculate Emergency Light Units
    Emergency Light Units
    28 = 28
  3. Calculate Exit Signs Required
    Exit Signs Required
    6 = 6
  4. Calculate Total Power Draw
    Total Power Draw
    310 = 310
  5. Calculate Battery Capacity
    Battery Capacity
    558 = 558

Figures and sources

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why don't Number of Exits or Battery Duration change my Emergency Light Units count?

Emergency Light Units is calculated purely from Total Floor Area, Total Corridor Length, and Stairwells — the physical space needing illumination coverage. Number of Exits instead drives Exit Signs Required, and Battery Duration only affects Battery Capacity and the Duration Compliant check, so none of those three connect back to the light unit count.

What happens if I set Battery Duration below 90 minutes?

Duration Compliant will flip to a non-compliant result, since NFPA 101 requires a minimum 90-minute (1.5-hour) battery backup duration for emergency egress lighting. This field lets you check an existing installation or a lower-cost battery pack against the code minimum rather than only ever assuming a compliant system.

Why is there a 20% safety margin on Battery Capacity?

The safety margin accounts for the fact that battery capacity fades over its service life due to charge/discharge cycling and age, so sizing to the bare minimum wattage-times-duration figure risks the system falling short of code duration well before the battery is due for replacement. Sizing in a margin up front is standard practice for emergency lighting battery packs.

Does this calculator verify actual illumination levels on the floor?

No — it estimates how many fixtures you likely need based on floor area and corridor length using conservative coverage assumptions (600 sq ft per unit, 30 ft corridor spacing), not a photometric calculation. Verifying the actual 1 foot-candle average / 0.1 foot-candle minimum / 40:1 uniformity requirements at floor level requires a point-by-point lighting layout, typically done by a lighting designer or fire protection engineer.

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