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Safe Room Size Calculator – Online Occupancy & Ventilation Check

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Safe Room Size Calculator

Instantly find the minimum recommended size for your tornado or residential safe room. Check occupancy, ventilation, and FEMA-based guidelines in one place.

1 – 50 people
Recommended Minimum sq ft

20

Floor area based on 5 sq ft per person (standing)
Ventilation Assessment
Enter data to see ventilation check

Frequently Asked Questions

According to FEMA P-320, a residential safe room should provide at least 5 square feet per standing person and 3 square feet per seated person. This safe room size calculator uses 5 sq ft/ person for standing occupants. Always check local building codes for additional requirements.

FEMA recommends either natural ventilation (passive openings equal to at least 3% of floor area) or mechanical ventilation supplying 15 CFM of fresh air per person. Our calculator checks if your room volume and air change rate meet these goals, helping you avoid CO₂ buildup during occupancy.

Absolutely. The calculator follows guidelines from FEMA P-361 and ICC-500 for tornado and hurricane safe rooms. It provides both occupancy sizing and ventilation checks—two critical factors for any severe weather safe room.

If your room fails the area or ventilation check, consider expanding the room, reducing the number of occupants, or adding mechanical ventilation with a higher CFM rating. The tool will highlight the exact shortfall so you can plan upgrades.

We base calculations on widely accepted FEMA and ICC standards. However, always consult a licensed engineer or local authority for final safe room design, especially in high-wind zones. This tool provides a quick pre-check for planning.
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