There is no single federal number that applies to every building, but there is a method that does: the 3-minute response window. The American Heart Association’s benchmark for AED placement is that a device should be retrieved and returned to the victim within 3 minutes of collapse.
That window — not a square footage formula or an employee headcount ratio — is the right starting point for figuring out how many AEDs your building actually needs.
Why 3 minutes specifically? A 2011 study published in AHA Circulation found that neurologically intact survival after out-of-hospital cardiac arrest was 49.6% when an onsite AED was used, compared to 14.3% when no AED was available before EMS arrived. Research across multiple large-scale public access defibrillation programs shows survival rates of 50% to 70% when defibrillation happens within the first 3 to 5 minutes. After 7 to 10 minutes without defibrillation, survival rates typically fall below 10%.
The right question to ask: “How many AEDs does our building need?” is not as useful as “Can we deliver a shock within 3 minutes from anywhere in this building?” Those two questions often yield the same answer for small buildings and completely different answers for large, multi-wing, or multi-floor ones.
The 3-minute rule in real terms
Three minutes sounds like a lot. It isn’t. Break down what actually has to happen:
That entire sequence plays out in 3 minutes with essentially no margin for getting lost, waiting for an elevator, navigating a locked door, or finding that the AED cabinet is behind a reception desk nobody knows how to open.
The airport model: Most major airport terminals place AEDs every 500 to 600 feet, keeping walking distance from any point to any AED within 60 to 90 seconds — leaving 90 seconds to get back with the device before the window closes. Airports are designed around strangers with no building knowledge, and they’ve concluded that roughly 1 AED per 500 to 600 linear feet is the coverage density that works. Most commercial buildings don’t need this density, but the underlying logic applies: plot the AED location, walk from the farthest point at a realistic urgent pace, time the round trip. If it exceeds 3 minutes, the coverage has a gap.
The walk test: the right way to calculate your AED count
This is the method the AHA and most AED program specialists recommend. It takes about 20 minutes to complete for a standard single-floor building.
- Pick a candidate location for your first AED — typically a high-visibility spot in a main corridor, lobby, or break room.
- Walk to the farthest accessible point in the building from that location. A real location: a corner office, a loading dock, a back stairwell — somewhere a person might actually collapse.
- Time the round trip. Start a stopwatch. Walk from that far point back to the AED location, grab the device, and walk back. Walk at a pace that reflects urgency but not sprinting — because most people retrieving an AED will be walking fast, not running, especially navigating stairs or operating a cabinet.
- Check the time. If the round trip takes more than 3 minutes, your single AED does not cover that corner of the building. Either the AED needs to move, or a second AED needs to be added.
- Repeat from new candidate locations until every reachable point in the building falls within a 3-minute round trip from at least one AED.
A few things the walk test surfaces that square footage formulas miss entirely:
- Locked areas and access barriers. A security-controlled wing, a keypad-protected server room, or an area behind a reception desk requires its own AED. The main corridor AED is unreachable from behind a locked door without adding 60 to 90 seconds for access.
- Stairwells and elevator banks. Never plan on an elevator during a cardiac emergency. Elevators are called, they wait, they stop at floors. In a genuine emergency, the elevator might take 90 seconds just to arrive. Each floor needs its own device — not coverage from the floor above or below.
- Physical obstacles. Long winding corridors, right-angle turns, split-level layouts, and buildings with multiple wings all extend walking time beyond what a straight-line distance calculation suggests.
Minimum coverage by building type
The following are not legal federal requirements. They are evidence-based coverage minimums based on the 3-minute response window and widely used by safety professionals, insurance carriers, and state PAD program guidance. For state-specific mandates, check the AED laws hub.
🏢 Single-story office / commercial
Under 10,000 sq ft: One AED, centrally located, typically covers the space if the layout is open.
10,000 to 50,000 sq ft: One to two AEDs. Apply the walk test from the farthest corners to confirm. Complex layouts with multiple wings usually need two.
Over 50,000 sq ft: Multiple AEDs positioned so no point is more than a 90-second walk from a device.
🏗 Multi-story building
At minimum, one AED per occupied floor — driven by elevator math. A person on the 8th floor cannot safely count on reaching an AED from the 6th floor within 3 minutes.
For large floor plates, apply the walk test per floor.
🏫 Schools
State law varies significantly — from device mandates to athletics-only requirements. Best practice for a standard K-12 campus is one AED per building, plus a dedicated AED for athletic facilities. Outdoor fields and gymnasiums are often further from interior AEDs than the walk test would suggest.
🏋 Fitness centers and gyms
High-risk environment due to physical exertion and elevated cardiac arrest incidence. Industry standard is at minimum one AED per exercise floor, with placement near the main workout area. Dedicated AED for pool areas where applicable.
🏟 Large assembly and event spaces
Higher occupancy plus a diverse age range plus event stress creates elevated SCA risk. AED density should account for peak occupancy scenarios, not normal weekday use. Outdoor venues require weatherproof enclosures and coverage for backstage and staff areas.
🏭 Manufacturing and warehouse facilities
Often overlooked because they’re not public-facing. Frequently have large floor plates, restricted access zones, loud environments where calls for help can’t be heard, and physically demanding work that increases cardiac risk. A 500,000 sq ft warehouse end-to-end may be a 5-minute walk at urgency pace — far beyond a single AED’s coverage.
Multi-story floor plate reference
| Floor plate size | Minimum AEDs per floor |
|---|---|
| Under 10,000 sq ft | 1 |
| 10,000 to 30,000 sq ft | 1–2 (walk test to confirm) |
| 30,000 to 50,000 sq ft | 2 |
| Over 50,000 sq ft | 2+ (walk test required) |
Factors that change the calculation
Beyond building size and layout, five factors push the AED count higher than the minimum.
🚑 EMS response time in your area
In a dense urban area where EMS is 4 to 5 minutes away, your internal response needs to happen before that. In a suburban or rural area where EMS might be 12 to 15 minutes out, the on-site AED is covering a much longer window and device redundancy becomes more important. One AED failure during a rescue in a 12-minute EMS response area has no backup.
👥 Occupancy density and population risk
A building with 500 employees has statistically higher daily cardiac risk than one with 20. Facilities serving older populations or those with known cardiac conditions should plan toward the higher end of coverage density.
🌙 After-hours coverage
If 200 people work in the building from 9 AM to 5 PM and 2 security guards are there at night, the after-hours response time for a single AED increases dramatically. A night custodian collapsing in a remote corridor has no realistic chance of being found within 3 minutes by 2 guards covering 200,000 square feet. After-hours occupancy patterns should factor into placement decisions.
⚠️ High-risk areas requiring dedicated coverage
Certain spaces generate disproportionate SCA risk regardless of overall building coverage. Dedicated AED placement is standard practice for:
- ⚡ Fitness facilities / gyms
- 🏊 Swimming pools / aquatic centers
- 🍽 Cafeterias and food service
- 🏥 Medical and dental suites
- 🖥 Keycard / biometric access areas
- 🚛 Loading docks and heavy equipment
🌳 Outdoor areas
Parking lots, athletic fields, outdoor courtyards, and building grounds are easy to forget in an indoor-focused coverage assessment. A cardiac arrest in a parking structure is not covered by the lobby AED if the structure is 400 feet away and access requires a stairwell or ramp.
The one calculation most organizations get wrong
Most facilities plan AED placement from a single central location outward. The walk test should work in both directions: from the central AED location to the farthest points, and from every high-risk or high-traffic area inward to the nearest AED.
The centrally located AED covers the average case. It’s the edge cases that result in deaths. A cafeteria at lunchtime has higher cardiac risk than an average corridor. A gym at 6 PM has higher risk than an average conference room at 2 PM. Placing coverage around the average case instead of the high-risk locations is the single most common AED placement mistake.
⚠️ The retrospective finding: When AED placement is reviewed after a cardiac arrest where the person died, the finding is almost always the same — the AED existed, it was 4 minutes and 20 seconds away instead of 3 minutes, and nobody ran the walk test before placing it.
Managing coverage across multiple buildings or locations
Knowing how many AEDs a building needs is one problem. Knowing whether the devices you have are actually rescue-ready across 12 buildings, 3 campuses, or 40 retail locations is a different scale of problem entirely.
AED Log is designed for exactly this: every AED, every building, and every location managed in one dashboard with the coverage picture visible across the whole program. Monthly inspection reminders go to the responsible person per location automatically, battery and pad expirations alert 60 and 30 days ahead, and every device’s status is visible without visiting each building manually. Pricing is based on the number of AEDs in your program, starting free on 1 AED.
💡 See every AED’s readiness status across every location — without visiting each building manually.
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