How Far Apart to Space Soffit Vents

Soffit vents in an attic.

Soffit vents help cool attic space by allowing air to circulate within the attic. These vents can prolong the life of your roof and reduce electricity bills by cooling the attic space. Soffit vents bring in fresh air and circulate the air through the attic space to cool and freshen the space.

Calculating Vent Space

Measure the length and width of the attic and multiply the two together. Take the solution and divide it by 150. The final number will be the total vent space needed for your attic. For example, 1,500 square feet of attic space requires 10 square feet of vent space.

Calculating Soffit Vent Space

Divide the smaller measurement of the vent you have selected by the larger measurement. For example, a 6x12 inch vent would have a vent space of 0.5 square feet.

Calculate Number of Vents

Next, divide the square footage of vent space required by the square footage of soffit vent you have selected. For the previous example, you would need 20 soffit vents.


You need to have an equal number of vents located at the bottom of the attic, or under the roof easement as you have at the top of the attic near a gable or ridge. Space the vents at the bottom and top of the attic equally according to house size.