How Many AEDs You Need: Size, Layout, and Time to Shock

How many automated external defibrillator (AED) units does your building really need? The answer is not only about square footage. It is about how quickly a responder can reach a victim of sudden cardiac arrest, retrieve an AED, and deliver a shock. Using time-to-shock, not just floor area, helps you right-size your program for the best possible outcome.

Why AED Quantity Depends on Time to Shock, Not Just Square Feet

The outcome driver is time

When a person collapses from cardiac arrest, every minute without defibrillation reduces survival chances. The most practical way to determine how many AEDs you need is to plan for a safe and fast time to first shock, often called the response interval. This is the period from collapse to the moment an AED delivers a therapeutic shock. The right number of devices is the number that brings that interval within an acceptable target for the vast majority of your occupants and visitors.

American Heart Association guidance notes that defibrillation within 3 to 5 minutes of collapse can produce survival rates of 50 to 70 percent. The earlier the shock, the better the odds.

Why area alone misleads

Two buildings with identical square footage can have very different AED needs. A wide-open gym floor allows quick movement, while a maze of corridors, locked doors, or split-level mezzanines creates delays. Elevators, security turnstiles, badge readers, and noisy production lines also slow response and can force longer routes. This is why relying on square feet per AED often underestimates what it takes to meet the 3-minute goal.

• Open layouts allow larger coverage per device.
• Compartmentalized or access-controlled spaces shrink practical coverage.
• Vertical travel and single points of entry often add critical seconds.

Instead of a one-size-fits-all ratio, build your plan around how quickly someone can reach an AED and return to the victim. That is the primary determinant of the number of AEDs required.

The 3-Minute Rule: Turning Travel Time Into Coverage Zones

From minutes to feet

A widely used planning target is a collapse-to-shock time of about 3 minutes. To support this, many programs aim to keep AED round-trip retrieval time close to 90 seconds. This leaves time for assessing the victim, opening the device, and placing pads. Converting travel time to distance helps transform your floor plan into coverage zones.

Planning rule of thumb used by many public access defibrillation programs: place AEDs so a responder can reach and return from the device in roughly 90 seconds under typical conditions.

Making a practical estimate

Use walking speed to translate time into distance. A brisk walking pace ranges from 250 to 300 feet per minute. If you allow about 90 seconds for the round trip, a responder can cover roughly 450 feet total, or about 225 feet each way. This becomes the initial coverage radius from an AED along real paths of travel, not straight lines through walls.

• Assumed walking speed: 250 to 300 ft per minute.
• Round-trip travel time target: about 90 seconds.
• Indicative one-way distance: 200 to 225 ft, adjusted for obstacles.

In open spaces, that suggests a theoretical circular coverage area around each device. In buildings with corridors, stairs, or locked doors, replace the circle with a path-based shape that follows hallways and stairs. Elevators introduce wait time and uncertainty, so favor stairs for planning. Add time penalties for vertical movement and access control to keep your estimate realistic.

Layout Factors That Increase AED Needs in Real Facilities

Barriers and path complexity

Every obstacle reduces effective coverage. Doors that latch, badge readers, security gates, and one-way corridors force detours that add crucial seconds. Long, linear facilities such as warehouses or concourses often require more AEDs placed at intervals, since walking distance accumulates quickly down a single spine.

Vertical travel and special zones

Multi-story buildings add complexity. Stairs can add 20 to 30 seconds per floor for many responders, and elevator wait times are unpredictable. Treat athletic spaces, fitness centers, manufacturing lines, and areas where older adults gather as high risk zones. These spaces often warrant closer placement or dedicated units, even when the rest of the building meets time targets.

OSHA encourages rapid access to defibrillation in the workplace, particularly where Emergency Medical Services response may be delayed. On-site AEDs bridge the time gap to first shock.

Occupancy and noise

Peak crowding, high ambient noise, and complex shift patterns all affect how quickly a responder can move and communicate. Busy lobbies, event venues, and cafeterias may be navigable off-hours but slow during peaks. Factor these real conditions into coverage assumptions and plan for the worst likely case, not only the average.

• Consider door hold-open policies and after-hours locking routines.
• Plan for shift overlaps and visitor surges.
• Account for construction zones or seasonal layout changes.

All of these elements influence how many AEDs a facility requires to maintain the 3-minute goal throughout the day and across the full footprint.

Step-by-Step Method to Calculate AEDs for Your Floor Plan

1) Set targets and gather inputs

Start by adopting a 3-minute collapse-to-shock objective. Collect scaled floor plans, occupancy patterns, known barriers, stair locations, and access control details. Identify on-site medical staff or trained responders if present.

2) Identify high-risk and high-traffic areas

Flag spaces with elevated risk or crowd density. Examples include fitness rooms, manufacturing cells with electrical or chemical hazards, auditoriums, cafeterias, athletic fields, and reception areas. Plan to reduce time to shock in these zones even if other areas are already well covered.

3) Map travel-time coverage

Choose candidate AED locations that are visible and centrally accessible, such as near elevators, main corridors, lobbies, security desks, and break rooms. Using a brisk walk speed of 250 to 300 ft per minute, draw path-based rings that represent approximately 200 to 225 feet of one-way travel. Add time penalties for stairs, turnstiles, and locked doors. Do not assume diagonal movement through walls; follow actual paths of egress.

Treat coverage like a network map. The goal is not geometric distance but real travel time along usable routes under typical conditions.

4) Count devices and validate with drills

Where coverage rings fail to overlap enough to keep all common locations within the 90-second retrieval target, add devices and repeat. Run timed drills during busy periods, then adjust positions to cut delays. If AEDs serve multiple floors via open atriums or interconnecting stairs, verify that a single device still meets time targets during congestion.

5) Account for staffing and access

Ensure AEDs are accessible whenever people are present. If spaces are used after hours or on weekends, either provide 24/7 access to existing AEDs or add units in publicly reachable areas. If security desks are unstaffed on nights or holidays, do not rely on them as the sole access point.

• Plan for redundancy where single-point failures could exceed time targets.
• Document your assumptions and revisit them after layout changes.
• Consider future growth, renovations, or new access controls that could alter travel time.

Real-World Scenarios and Example Calculations

Scenario 1: Single-floor office, 60,000 sq ft

An open-plan office with two long main corridors and multiple glass meeting rooms has few hard barriers. Using a 200 to 225 foot one-way travel distance, a single AED might appear sufficient by area. However, meeting room clusters and badge-controlled suites create detours.

• Place 2 AEDs near the central crossroads and the opposite corridor end.
• Add a third unit if after-hours access to one wing is restricted.
• Ensure visible 3D signage at corridor intersections.

Result: 2 to 3 AEDs, validated by drills during peak meeting times.

Scenario 2: Warehouse, 100,000 sq ft, long and narrow

A rectangular warehouse with a single central aisle and racked storage requires walking long distances. Forklift traffic and noise further slow movement.

• Place AEDs at the shipping dock, midpoint of the main aisle, and receiving area.
• Consider an additional unit near the break room if it sits off the main spine.
• Use wall-mounted cabinets with audible alarms to aid location in noisy zones.

Result: 3 to 4 AEDs, spaced roughly every 200 to 250 feet along travel paths.

Scenario 3: Multi-story school, three floors plus gym

A school has stairwells at each end and a central lobby. Events in the gym drive peak occupancy. Relying on a lobby AED to cover the gym through crowded hallways is risky.

• Install one AED on each floor near central stairwells.
• Place a dedicated unit at the gym entrance or athletic trainer office.
• Ensure field access with a portable AED in a charged case for outdoor sports.

Result: 4 to 5 AEDs, providing floor-by-floor and athletic coverage.

Scenario 4: Healthcare office building, mixed tenants

A multi-tenant building includes dental and cardiology suites with patient populations at greater risk. After-hours access varies by tenant and elevator security increases travel time.

• Place AEDs at the main lobby, each elevator lobby, and near high-risk clinical suites.
• Coordinate with building management so lobby units remain accessible during extended hours.
• Label locations in the shared emergency plan and tenant handbooks.

Result: 4 to 6 AEDs depending on floor count and elevator placement.

Scenario 5: Event venue, arena concourse

Arena concourses are circular, crowded, and noisy during events. Funnel points at concessions and restrooms create bottlenecks. Straight-line distance underestimates travel time.

• Position AEDs at each quadrant of the concourse and at floor tunnels.
• Provide one unit in the security command post and one for floor-level staff.
• Train ushers to guide runners and clear paths during emergencies.

Result: Multiple AEDs, typically every 200 to 250 feet along the concourse with duplicates near high-density zones.

Placement, Signage, and Program Practices That Maximize Coverage

Put AEDs where people will look first

Visibility and accessibility are as important as quantity. Place devices in brightly lit, common areas along primary travel routes: main lobbies, near elevators and stairwells, at security desks, outside restrooms, and near athletic spaces. Avoid locked rooms or behind reception counters that may be unstaffed. Cabinets with audible alarms deter tampering and help bystanders locate the unit quickly.

• Mount devices 48 to 54 inches to the handle for universal reach.
• Use projecting 3D signs at corridor intersections.
• Keep paths clear and free of storage that narrows corridors.

Plan for redundancy and off-hours

If the building is occupied nights or weekends, AEDs must be reachable without special keys or badges. Redundancy is critical where a single elevator bank, turnstile, or locked door could isolate a device.

Where access is restricted or response times vary widely, provide an additional AED rather than relying on a single device to serve multiple security zones.

Training, maintenance, and integration

Even the perfect number of units will not save lives without a functional program. Train staff in CPR and public access defibrillation, test your response plan with realistic drills, and maintain devices according to manufacturer instructions. Track pad and battery expirations, document inspections, and keep spare pads, including pediatric if appropriate for your population.

• Conduct monthly visual checks and after-use readiness inspections.
• Replace pads and batteries by expiration or after use.
• Register AED locations with local EMS if your jurisdiction supports it.
• Post clear instructions and emergency numbers at each cabinet.

Many manufacturers recommend at least monthly readiness checks. Some jurisdictions also require program oversight, medical direction, and notification to local EMS. Verify your state and local requirements.

Conclusion

Determining how many AEDs your facility needs starts with a simple idea, reach a victim and deliver a shock within about 3 minutes. Map real travel paths, account for barriers and vertical movement, then place enough devices so most people are within roughly 90 seconds of round-trip retrieval.

MyAED can help you calculate coverage, choose the right devices, and design a complete program with cabinets, signage, and training. Explore our AED bundles and accessories, or contact our team for a no-obligation site assessment to right-size your plan and improve readiness.