Enter the total square footage of the addition and the property’s value per square foot to determine the ADU cost.

ADU Cost Formula

The following formula is used to calculate the cost of an ADU.

ADUc = A * PV * .85
  • Where ADUc is the cost of the addition dwelling unit ($)
  • A is the total square footage of the addition (ft^2)
  • PV is the price per square foot value of the property ($/ft^2)

To calculate the ADU cost, multiply the area by the price per square foot, then multiply by .85.

What is an ADU Cost?


An ADU cost is defined as the total cost to construct an accessory dwelling unit. These units are built on single-family lots but are separate from the main house.

The cost of these units is typically 85% of the per square foot value of the property.

For example, if the property had a value of $100 per square foot, then the ADU cost would be $85 per square foot.

How to calculate ADU cost?

Example Problem:

The following example problem outlines how to estimate the cost of an ADU.

First, determine the value of the property on a square foot basis. In this example, the property has a value of $500 /ft^2.

Next, determine the size of the ADU. This ADU will have a total size of 300 square feet (ft^2).

Finally, calculate the ADU cost using the formal above:

ADUc = A * PV * .85

ADUc = 300 * 500 * .85

ADUc = $127,500.00