How Many Soffit Vents Do I Need? Soffit Vent Calculator + Chart

When adding soffit vents to an attic, you need to know how many soffit vents you need. More specifically, you want to figure out how much soffit vents you need (square feet of soffit). We are going to show you how you can easily estimate the number of soffit vents you need in the attic.

Namely, soffit vents are perforations that allow for inflow and outflow of air in the attics. You can have all kinds of soffit vents, from standard 8×16 inch soffit vents, under eave soffit vents, to continuous soffit venting. Correctly sizing soffit vents will extend the roof lifespan, reduce heating and cooling costs, prevent mold growth, and so on.

First, we’ll show the math. Afterward, you can use these 2 very easy resources (based on the calculations) to figure out how many soffit vents you need:

1. Soffit Vent Calculator. Here you insert the attic square footage, and the calculator will immediately determine how many square feet of soffit vents you need. On top of that, it will also tell you how many standard 16×8 inch soffit vents is that.
2. Soffit Vent Size Chart. We have calculated the size and number of soffit vents you need for attics ranging from 100 sq ft to 2,000 sq ft. All the soffit vent sizes and numbers of standard 16×8 inch vents are summarized in a neat chart, found below the calculator.

Alright, here is a rule of thumb the company Soffit itself recommends for sizing soffit vents:

Use 1 sq ft of soffit vents per every 150 sq ft of the attic.

That means that a 150 sq ft attic will need 1 sq ft of soffit, 300 sq ft attic will need 2 sq ft of soffit, and so on. Based on this, we can formulate an equation for calculating how many sq ft of soffit you need for any attic:

Soffit Vent Area = Attic Square Footage / 150

Example: Let’s say you have a 900 sq ft attic. What size soffit vent area do you need, and how many soffit vents is that? Let’s use the equation above like this:

Soffit Vent Area (900 Sq Ft) = 900 Sq Ft / 150 = 6.00 Sq Ft Of Soffit Vents

For a 900 sq ft attic, you would need 6 sq ft of soffit vents. If you are using the standard 16×8 soffit vents (1 standard soffit vent has 0.89 sq ft area), you would need 7 standard soffit vents (7/0.89 = 6.74 vents, and we round it up to 7 soffit vents).

This is the basic calculation. You can do it by hand, or you can use the following Soffit Vent Calculator (you will get soffit vent square footage, as well as a number of standard 16×8 soffit vents you need). Below the calculator is the all-encompassing soffit sizing chart for 100 sq ft to 2,000 sq ft attics:

Soffit Vent Calculator (Square Footage + Number)

Here is how this calculator works:

Let’s say you have a 1,500 sq ft attic. How many soffit vents do you need for a 1,500 sq ft attic? Just slide the attic square footage slider to ‘1500’, and you get these results:

For a 1,500 sq ft attic, you need 10 sq ft of soffit vents. If you are using the standard 16×8 vents, you would need 12 of those to ventilate your attic adequately.

This is just one example. Here is the full chart from the smallest to the biggest attics:

Soffit Vent Size And Number (Chart)

As we can see, the size and number of soffit vents increases linearly with increasing attic size. Basically, smaller attics with 1,000 sq ft or below will need up to 8 soffit vents (standard 16×8 sizes).

With bigger attics (1,500 sq ft and above), it’s not uncommon to add more than 10 sq ft of soffit vents. You can use continuous soffit vents for that or more than 12 standard soffit vents.

Hopefully, with the calculator and this chart, you can now adequately figure out how many soffit vents you need for your attic. If you need any help, you can use the comment section below, give us some numbers, and we can solve this question for your attic together.