The AED Quantity Calculator answers one question: how many AEDs does your facility need to meet the AHA 3-minute rule? The math underneath is straightforward, walking-speed-derived round-trip retrieval against the AHA-recommended collapse-to-defibrillation window. This article documents the formula, the assumptions, and the edge cases the calculator handles.
The core formula
Translated into plain English: divide square footage by 50,000 (the practical coverage radius for a single AED on a single floor); divide floor count by 2 (the practical vertical coverage per AED in mid-rise buildings); count distinct operational zones (gym, athletic field, kitchen, etc.) that need their own unit; add outdoor units if the facility includes athletic fields or outdoor work zones. Take the maximum.
The 3-minute rule, derived
1
0 to 60 seconds: recognition + alert
Bystander recognizes cardiac arrest, calls 911, or alerts staff. AHA documents that this typically takes 30 to 60 seconds.
2
60 to 150 seconds: retrieval round-trip
Available time for someone to retrieve the AED and return. At 3.5 ft/sec brisk walking, 90 seconds = 315 ft of round-trip, meaning ~150 ft each direction.
3
150 to 180 seconds: pad placement + shock
Apply pads, AED analyzes, and deliver shock if advised. AHA target is shock-by-180-second-mark.
Verified statistics behind the math
3 min
AHA shock-by targetSource: AHA
~10%
Survival drop per minute delaySource: AHA
3.5 ft/s
Average brisk walking paceSource: Established gait research
Edge cases the calculator handles
- Multi-floor buildings: Stair-climbing time doubles the per-floor retrieval cost. The calculator applies a floor-count multiplier per multi-floor placement math.
- Industrial floor plates: Forklift-traffic aisle planning reduces effective coverage. See warehouse coverage.
- Outdoor zones: Athletic fields and outdoor work zones get dedicated units regardless of indoor count.
- Cold storage: Refrigerated zones require AEDs outside the cold perimeter (most AEDs are rated for standby no colder than 32°F to 50°F, depending on model).
What the calculator doesn’t model
- EMS response time, context only, not factored into AED count
- State compliance overlays, verify with AED Laws by State
- Specific brand or model selection, that’s what Find Your Perfect AED handles
- Detailed budget, see AED Cost Calculator
Frequently Asked Questions
What is the AHA 3-minute rule?
AHA public-access guidance targets a shock within 3 to 5 minutes of collapse. This calculator uses the stricter 3-minute end.
How does the calculator handle multi-floor buildings?
It applies stair-climbing time per floor: ~20 to 25 seconds per floor, climbing up, slower than horizontal walking. Floor-count divider reduces effective coverage.
Does the calculator factor in EMS response time?
No, EMS context is informational. AED count is based on on-site retrieval math.
Why 50,000 sq ft per AED?
That’s the empirical coverage for a single-floor open layout with 3.5 ft/sec walking speed and 90-second round-trip retrieval (about 150 ft each way), derived from the 3-minute rule.
Can I trust the calculator for compliance?
For device count, yes. State mandates may require additional units beyond the 3-minute math, verify with AED Laws by State.
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Sources & References
Disclaimer: Methodology for planning purposes. State-specific compliance may require additional units.
