Emergency Lighting Battery Calculator
Use this emergency lighting battery workflow for early battery capacity screening when load, runtime, voltage, derating, efficiency, and reserve assumptions are known.
- Load energy
- Wh
- Usable factor
- x
- Base battery capacity
- Wh
- Required battery capacity
- Wh
- Required battery capacity
- Ah
Calculation details
- Calculation basis
- Selection boundary
Recent results
Formulas
- Load energy Wh = emergency load watts x runtime hours
- Usable factor = usable capacity percent / 100 x efficiency percent / 100
- Base battery Wh = load energy Wh / usable factor
- Required battery Wh = base battery Wh x (1 + reserve percent / 100)
- Required battery Ah = required battery Wh / battery voltage
Use this calculator
Estimate load energy, usable factor, base battery Wh, required battery Wh, and required Ah from load, runtime, voltage, usable capacity, efficiency, and reserve.
Read the result
Review the calculated values with their displayed units and assumptions. The result is a planning aid for the stated inputs, not a final equipment or installation decision.
Check before final work
This emergency lighting battery estimate is capacity arithmetic only. It does not approve emergency lighting code runtime, listed equipment, charging, transfer, temperature derating, inspection, or code compliance.
FAQs
Does this prove emergency lighting compliance?
No. It estimates battery capacity only. Emergency lighting runtime, listing, transfer, and inspection requirements need separate review.
Why include usable capacity and efficiency?
They account for capacity that may not be usable and conversion losses before reserve is added.
Can this select a battery model?
No. Battery chemistry, charger, temperature, enclosure, and manufacturer requirements must be checked separately.