Fire Alarm Calculators: Battery Sizing, Voltage Drop & More
Field-ready calculators for system design, troubleshooting, and quick checks. Each tool provides the math, a plain-language result, and practical context so you can use the number instead of just looking at it.
Most Used
Fast access to the calculations you are most likely to need in the field.
Detection & Notification
Layout and circuit planning
Power & Conductors
Battery, wire, and raceway checks
Network & Troubleshooting
Diagnostics and field helpers
Application
Planning and code-support tools
Ground Fault Diagnostic
Simulate expected meter readings for a ground fault, or diagnose fault side and approximate leakage from real measurements.
Resistor Selector
Find the nearest standard value, or compute R from voltage/current or LED parameters.
Battery Sizing (Standby + Alarm)
Estimate amp-hours for a 24V panel.
Voltage Drop
Calculate a two-wire circuit using one-way length and copper conductor resistance. Add the device minimum voltage for an immediate pass/fail check.
How this is calculated
Wire Gauge Selector
Suggest minimum AWG to meet a % drop target.
NAC Load Planner
Sum device currents and compare to a circuit capacity.
| Description | Per-device (mA) | Qty |
|---|
Speaker / Amplifier Load
Sum speaker taps and compare to amplifier capacity.
| Location / note | Tap (W) | Qty |
|---|
Compressor Wire Size Selector
Select minimum Cu AWG to satisfy ampacity and voltage-drop limits.
DIP Switch Address Helper
Build or decode DIP positions as a binary value.
Occupant Load NFPA 101–style
Pick a use group & subtype to auto-fill a factor from your local JSON library, or enter a factor directly.
/resources/calculators/occupant-load-factors.json. Mixed uses: calculate separately then sum.
Optional: Egress capacity check
Enter capacity factors used by your jurisdiction (stairs vs. level components).
Conduit Fill Calculator
Pick raceway type, trade size, and wire size to see max wire count and whether your requested quantity fits.
Auto uses 53% for 1 conductor, 31% for 2 conductors, and 40% for more than 2 conductors.
Smoke Detector Spacing
Estimate a basic spot-type smoke detector layout for a smooth, flat rectangular ceiling using the detector's listed spacing.
What this tool assumes
Heat Detector Spacing
Estimate a basic spot-type heat detector layout and apply the common ceiling-height spacing reduction factor to the detector's listed spacing.
How the ceiling-height adjustment works
Candela Coverage & Count
Estimate how many wall-mounted visible notification appliances may be needed for a rectangular room, then show a conceptual coverage-zone layout.
Horn Audibility / Coverage
Use free-field inverse-square sound loss to estimate how far a horn remains above a target sound level, then lay out a conceptual room grid.
How inverse-square sound loss is used
Fiber Loss Budget
Estimate passive link loss and compare it with the optical power budget of the transmitter/receiver pair.
How to use these fire alarm calculators
These free tools help technicians organize calculations for fire alarm service, layout, and troubleshooting. Start with current data for the actual panel, power supply, devices, and cable. Each result explains the math and the checks needed before using it on a project.
Fire alarm battery sizing
The battery calculator combines standby amp-hours and alarm amp-hours, then applies the selected allowance. The calculation is: [(standby current in amps × standby hours) + (alarm current in amps × alarm minutes ÷ 60)] × allowance. Convert milliamps to amps by dividing by 1,000.
Choose durations and allowances from the applicable project requirements and equipment documentation. Include every load powered by that battery set in the correct operating state. The two batteries used in series for a typical 24-volt system retain the amp-hour rating of one battery; their amp-hour capacities do not add together. Confirm approved battery sizes, charger capacity, and enclosure limits. Read the fire alarm battery sizing guide for the full workflow.
Voltage drop and notification circuits
The voltage drop calculator uses circuit current, one-way cable length, and conductor resistance to estimate the drop on a two-wire circuit. Use the device and power supply documentation to establish the minimum permitted voltage and evaluate the circuit under the appropriate operating conditions.
Use results with the installed system
A calculated result is a starting point for verification. Confirm equipment compatibility, adopted requirements, approved drawings, and the manufacturer's calculation method. For related field checks, use the troubleshooting trees and panel cheat sheets.