Calculate flood vent size or enclosed area from the other using the 1 sq in per 1 sq ft flood opening rule with unit conversions.

Flood Vent Calculator

Enter exactly one value to calculate the missing variable

Note: This uses the prescriptive minimum of 1 in² of net open area per 1 ft² of enclosed area (a code/NFIP sizing rule), not a geometric unit conversion.

Flood Vent Size Formula

The following example problem outlines the steps and information needed to calculate the Flood Vent Size.

FVS = A \times \left(\frac{1\ \text{in}^2}{1\ \text{ft}^2}\right)

Variables:

  • FVS is the required total net open area of flood vents (square inches)
  • A is the enclosed area requiring flood openings (ft2) 

To calculate the flood vent size, use the prescriptive minimum of 1 square inch of net open area per 1 square foot of enclosed area. Under this rule, the required flood vent size in square inches is numerically equal to the enclosed area in ft2 (this is a regulatory sizing rule, not a geometric unit conversion).

How to Calculate Flood Vent Size?

The following steps outline how to calculate the Flood Vent Size.

  1. First, determine the enclosed area (ft2) requiring flood openings. 
  2. Next, gather the formula from above: FVS = A × (1 in2/ft2).
  3. Finally, calculate the Flood Vent Size.
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

enclosed area (ft2) = 900

FVS = A × (1 in2/ft2)  = ?