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Calcimator

Shelter Capacity Calculator

Calculate emergency shelter capacity from floor area, per-person space standards, and resource needs.

About this calculator

Determining how many displaced people a building can safely shelter starts with usable floor area, not total square footage. This calculator first strips out space that can't be used for sleeping — hallways, kitchens, storage — by applying your entered "usable percentage" to the total floor area, then divides that usable area by a per-person space standard to get maximum capacity (rounded down, since partial spots don't count). The default of 60 square feet per person reflects FEMA's recommended standard including circulation and common areas; the American Red Cross's stricter minimum for sleeping-only space is 40 sq ft, so switching to that number will noticeably raise the reported capacity. From total capacity, the calculator carves out a percentage of ADA-accessible spots (rounded up) and treats the remainder as standard spots, though it doesn't adjust the space-per-person figure for the larger footprint ADA spots typically require in practice.

It then layers on resource planning using established humanitarian standards: one restroom or portable toilet per 40 people (the SPHERE handbook's short-term guideline), three gallons of water per person per day (one for drinking, two for sanitation), and three meals per person per day, both scaled by your chosen shelter duration. Cots needed simply equals total capacity, without separately accounting for aisle space between cot rows. Because these are planning-level ratios rather than a fire-code or engineering review, always confirm final capacity against your facility's actual life-safety code and accessibility requirements before activating a shelter.

Inputs

sq ft
%
%

Results

Max shelter capacity

58

Usable area (sq ft)3,500
Standard spots52
ADA-accessible spots6
Cots needed58
Restrooms / port-a-potties2
Daily water (gal)174
Total water (gal)522
Total meals needed522
How to Use This Calculator
  1. Enter Total Floor Area (sq ft) of the shelter facility.
  2. Set Sq Ft per Person — SPHERE standard is 3.5 m2 (37.7 sq ft) per person minimum.
  3. Enter Usable Area (%) to exclude walls, equipment, and circulation.
  4. Set ADA-Accessible % to ensure compliance with accessibility requirements.
  5. Review Max Shelter Capacity and ADA-accessible spaces to plan shelter activation.

How the result changes with Total floor area (sq ft)

Total floor area (sq ft)Max shelter capacity
2,50029
3,75043
7,50087
12,500145

What each input means

Total floor area (sq ft)
Total floor area of the building or facility.
Sq ft per person
Space per person (Red Cross min: 40, FEMA recommended: 60).
Usable area (%)
Percentage of floor area usable for sheltering after excluding hallways, kitchens, and storage.
Shelter duration (days)
Expected number of days the shelter will be operational.
ADA-accessible (%)
Percentage of spots designated as ADA-accessible.

What each result means

Max shelter capacity
Maximum number of people the facility can shelter.
Usable area (sq ft)
Actual floor area available for sheltering.
Standard spots
Number of standard sleeping spots.
ADA-accessible spots
Number of ADA-accessible sleeping spots.
Cots needed
Number of cots to acquire or deploy.
Restrooms / port-a-potties
Minimum restroom facilities needed (1 per 40 people, SPHERE standard).
Daily water (gal)
Daily water requirement at 3 gal/person (1 drinking + 2 sanitation).
Total water (gal)
Total water needed for the full shelter duration.
Total meals needed
Total meal servings for the full shelter duration (3 meals/person/day).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Total floor area (sq ft) = 5000, Sq ft per person = 60, Usable area (%) = 70, Shelter duration (days) = 3 = 5 input(s) provided
  2. Calculate Max shelter capacity
    Max shelter capacity
    58 = 58
  3. Calculate Usable area
    Usable area = totalFloorAreaSqFt * (usablePercentage / 100)
    3500 = 3500
  4. Calculate Standard spots
    Standard spots
    52 = 52

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does the calculator use usable area instead of total floor area?

Sheltering people requires open floor space for cots and movement, not the building's full footprint — hallways, kitchens, storage rooms, and mechanical spaces can't hold cots even though they count toward total square footage. The 'usable percentage' input lets you strip those areas out before dividing by the per-person space standard, which keeps the capacity estimate from overstating how many people the building can actually sleep.

Should I use the FEMA 60 sq ft or Red Cross 40 sq ft standard?

FEMA's 60 sq ft per person includes room for circulation and common areas and is the more conservative, comfort-oriented figure, while the Red Cross's 40 sq ft is a stricter minimum meant for sleeping space alone in a fast-moving emergency. If your shelter needs to squeeze in more people during a short-notice activation, 40 sq ft yields a noticeably higher maxCapacity; for longer-duration shelters where comfort and dignity matter more, 60 sq ft is the safer planning figure.

Why doesn't the ADA-accessible spot count reduce total capacity further?

The calculator carves ADA spots out of the already-computed maxCapacity by percentage rather than resizing them to their real-world footprint, which is typically larger than a standard 40-80 sq ft spot to allow wheelchair turning radius and companion space. In practice this means the reported standardSpots + adaSpots total is a slight overestimate of true capacity once you actually lay out ADA-compliant spacing — treat the ADA percentage as a planning flag, not a precise area calculation.

How is the daily water requirement of 3 gallons per person calculated?

It's the sum of two humanitarian planning figures: 1 gallon per person per day for drinking and 2 gallons per person per day for sanitation and hygiene, giving 3 gallons total. That daily figure is then multiplied by both maxCapacity and your entered shelter duration in days to produce totalWaterGallons, so a longer-duration shelter or higher capacity scales water needs linearly.

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