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Roof & Attic Vent Calculator

Use the table below to find the necessary number of vents for an attic of a particular size. Locate the square footage of the area (by multiplying the width by length, in feet) on the left to see how many vents you will need of the desired style.

Needed for exhaust
Ridge Vents
Net Free Vent Area Needed at Soffit (Undereave)
Sq. In. NFVA @ Upper Roof
Minimum ft. of Heat & Moist. ridge
Minimum ft. of ridge vent
Metal Dome
Metal Slanted Dome w/ screen
Plastic Slanted Dome w/ screen
Metal Square Top Vent
Needed for Intake at Soffit Sq. Inches NFVA at Soffits
Square Footage of Area
(to be Vented)
500 120 6 10 1 2 2 2 120
600 144 7 11 1 2 2 2 144
700 168 8 13 1 3 3 3 168
800 192 10 15 1 3 3 3 192
900 216 11 17 1 4 4 4 216
1000 240 12 19 1 4 4 4 240
1100 264 13 21 1 4 4 5 264
1200 288 14 23 2 5 5 5 288
1300 312 16 25 2 5 5 6 312
1400 336 17 27 2 6 6 6 336
1500 360 18 29 2 6 6 7 360
1600 384 19 30 2 6 6 7 384
1700 408 20 32 2 7 7 8 408
1800 432 22 34 3 7 7 8 432
1900 456 23 36 3 8 8 8 456
2000 480 24 38 3 8 8 9 480
2100 504 25 40 3 8 8 9 504
2200 528 26 42 3 9 9 10 528
2300 552 28 44 3 9 9 10 552
2400 576 29 46 4 10 10 11 576
2500 600 30 48 4 10 10 11 600
2600 624 31 49 4 10 10 12 624
2700 648 32 51 4 11 11 12 648
2800 672 34 53 4 11 11 13 672
2900 696 35 55 4 12 12 13 696
3000 720 36 57 5 12 12 14 720

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