sq in net free area
Roof Ventilation Calculator
Estimate required attic ventilation from attic area and ventilation ratio assumptions.
Roofing estimate note
Roofing calculators on ToolsBing are planning estimates only. Confirm roof geometry, pitch, local code, structural limits, wind and snow loads, manufacturer coverage, underlayment rules, ventilation requirements, drainage design, fall protection, permits, and installation details with a qualified roofer, contractor, engineer, supplier, or inspector before ordering or building.
Enter roofing inputs
Estimated result
This is an early buying, sizing, or planning number before roof-field verification.
Confirm pitch, measurements, code, manufacturer coverage, waste, drainage, ventilation, and safety requirements.
Formula and assumptions
Net free area = attic area ÷ ventilation ratio × 144 square inches, adjusted for reserve
Use this result as a preliminary roofing estimate. Real projects may require roof inspections, structural review, wind and snow design, waterproofing details, ventilation balancing, drainage checks, permits, and professional installation.
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Check before using this result
Verify the inputs, units, assumptions, and any local rules that apply. For financial, health, engineering, or construction decisions, confirm the result with a qualified professional or an authoritative source.