Total NFA Needed
720 sq in
Ridge Vent
20 ft
Soffit Vents
6
Est. Cost
$172
720 sq in
360 sq in
20 ft
$172
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Price as of Jul 24, 2026. Product prices and availability are accurate as of the date indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
Inputs
Result
1,500 / 300 = 5 sq ft NFA = 720 sq in. Split 50/50: 360 sq in intake, 360 sq in exhaust. Ridge vent: 360 / 18 = 20 ft. Soffit vents: 360 / 65 = 6 vents.
Inputs
Result
2,000 / 150 = 13.33 sq ft = 1,920 sq in. Hot climate: ×1.2 = 2,304 sq in. Pitch adjustment (8:12): ×1.04 = 2,396 sq in. Ridge: 1,198 / 18 = 67 ft. Soffit: 1,198 / 65 = 19 vents.
The standard rule is 1 square foot of net free area (NFA) for every 150 square feet of attic floor space (1:150 ratio). With a ceiling vapor barrier installed, you can use the less restrictive 1:300 ratio. Split ventilation 50/50 between intake (soffit) and exhaust (ridge).
| Attic Size | NFA (1:150) | NFA (1:300) | Ridge Vent (ft) |
|---|---|---|---|
| 1,000 sq ft | 960 sq in | 480 sq in | 27 ft / 14 ft |
| 1,500 sq ft | 1,440 sq in | 720 sq in | 40 ft / 20 ft |
| 2,000 sq ft | 1,920 sq in | 960 sq in | 54 ft / 27 ft |
The 1:150 ratio requires 1 sq ft of NFA per 150 sq ft of attic space and is the default requirement. The 1:300 ratio allows half as much ventilation but requires a ceiling vapor barrier and balanced intake/exhaust ventilation to qualify.
Mixing exhaust types is not recommended. When ridge vents and gable vents or turbine vents are combined, the lower exhaust point (gable/turbine) can act as an intake, short-circuiting the airflow pattern and reducing overall ventilation effectiveness.
Steeper roofs create a larger attic volume, which increases the chimney effect and can improve natural convection. However, the larger volume also means more air to move. For roof pitches above 6:12, add approximately 2% more NFA per additional pitch increment to account for the increased volume.
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Last Updated: Jul 24, 2026
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