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The Ultimate Guide to Measuring Net Internal Area Accurately

In the world of commercial real estate, a building’s Net Internal Area (NIA) is important for communicating the usable space, calculating lease rates, and estimating a property's value. This article discusses the nuances of NIA, walks you through the steps in calculating it, and describes how modern tools like RoomSketcher can streamline this process.

Blog | Floor Plans
Net internal area
Tony Gillen

What is Net Internal Area (NIA)?

Net Internal Area (NIA) is a measurement used in commercial real estate to determine the “usable space” within a building. Usable space means the available areas for tenants' exclusive or sole use, such as offices, retail space, labs, and manufacturing. Areas excluded from an NIA calculation include common areas such as shared lobbies, restrooms, or elevators. 

NIA is an essential metric for landlords and tenants, as it provides a standardized way to assess the actual area available for occupation and use within a building.

Note that definitions of NIA - including which areas count towards it and which don’t - vary worldwide. Hence, it's best to check with local authorities or a professional appraiser for your location's most used measurement standards. Many countries are moving towards International Property Measurement Standards (IPMS), developed by more than 80 professionals and non-profit organizations, to document international property measurement standards.

Practical Tips on How to Measure and Calculate Net Internal Area

NIA is basically the total internal area of a building minus the interior walls and common areas. In other words:

NIA = Gross Internal Area − (Interior Walls + Common Areas)

Here are a couple of ways to calculate NIA:

Option 1: Use an existing blueprint or floor plan

If you have an existing blueprint or floor plan for the building, you can import it into floor plan software like RoomSketcher. With RoomSketcher’s built-in area calculator, you can get your NIA result in seconds - just click to exclude the common areas on the floor plan and then choose the “Internal Zone Area” calculation (which automatically excludes the internal walls for you).

See Calculate the Total Area of a Floor Plan for more information on RoomSketcher’s area calculations.

Option 2: Measure onsite

You can also measure up the property if you don’t have access to an existing floor plan.  If you know the building’s GIA, you can measure the internal walls and common spaces and subtract them. Or, if you don’t know the building’s GIA, you can add up all the usable space to calculate the NIA. For example:

  1. Start with a walkaround - Walk around the property to get an idea of the shape and number of floors.
  2. Sketch the external walls on paper or tablet - Make a sketch of the property shape or create a digital sketch using floor plan software on your tablet. 
  3. Note the Usable Space vs the Common Space - Locate the areas or rooms that are usable space and mark these on your sketch. Also, note the common areas intended to be shared among tenants so you do not include them in the calculation.
  4. Get the measurements - Now, use a tape measure, roto wheel, or a laser to determine the size of any room or area that counts as usable space. It’s helpful to divide the areas into rectangles and measure from the inside of all walls.  Once you’ve measured up one side of a rectangle, go ahead and measure the other direction. Remember, don’t include any common areas or shared spaces among tenants.  
  5. Do the math - Multiply the length and width of each rectangle to calculate its size. Add together all the rectangular usable areas on the floor. Repeat for all floors, and sum the result to calculate the building’s Net Internal Area (NIA).

What Does Net Internal Area Include?

NIA describes how much “usable space” a building’s interior contains. Examples of areas to include in an NIA measurement are:

Top RoomSketcher Tip

"Because standards vary slightly worldwide, check with your local authorities for a complete list of the standard inclusions in your area. For example, suppose you use the International Property Measurement Standards (IPMS). In that case, your calculation would include columns and tenant portions of shared walls (also called party walls.)"

Net internal area - NIA inclusions

Net Internal Area Exclusions

NIA calculations exclude common areas (also called balance areas) because they are not considered specific to a particular occupant. Examples include:

Top RoomSketcher Tip

"Because standards vary slightly worldwide, check with your local authorities for a complete list of the standard exclusions in your area."

Net internal area - NIA exclusions

NIA Compared: How It Differs from Other Measurement Standards

Let's take a look at the differences between Net Internal Area (NIA) and other calculations. For additional information on measurement standards, see GIA Explained, The Ultimate Guide to Understanding Property Size, and What is Gross Living Area, and How do you Calculate it?

real estate measurement guide

Net Internal Area (NIA) vs. Gross Floor Area (GFA)

The Gross Floor Area (GFA) is generally defined as the total area of the building. GFA includes external walls and all areas inside the structure, including entrance lobbies and other common areas, lifts/elevators, stairwells, mechanical equipment areas, corridors, etc. In contrast, NIA does not include external or internal walls or common areas.


Net Internal Area (NIA) vs. Gross Internal Area (GIA)

GIA (also known as Gross Internal Floor Area) includes everything measured from inside the external walls, including internal walls and common areas in a building. In contrast, NIA does not include the internal walls and common areas.


Net Internal Area (NIA) vs. Gross Living Area (GLA)

Gross Living Area (GLA) is used for residential rather than commercial properties. As such, the measurements are not related.  To learn more about GLA, see What is Gross Living Area, and How do you Calculate it?


Net Internal Area (NIA) vs. Gross Building Area (GBA)

Net Internal Area describes the amount of usable space within a building and does not include external walls, internal walls, or common spaces. In contrast, Gross Building Area describes the total area of a building and includes common areas as well as internal and external walls.

GBA is similar to Gross Floor Area (GFA) in the commercial world.


The Importance of Accurate NIA Calculation

The Net Internal Area is important for various purposes:

Thus, NIA must be measured correctly and using the agreed-upon standards in your area. 

Frequently Asked Questions About NIA

Making NIA Measurements Easy and Accurate

In summary, Net Internal Area is an important metric in commercial real estate that helps determine the actual usable space within a building. It plays a role in lease agreements, space planning, and overall efficiency assessments for both landlords and tenants. It is one of several standard measurements used in commercial real estate.

To accurately calculate NIA, you can measure up the usable space in a building or use Floor Plan Software, like RoomSketcher, to improve the process of measuring NIA.

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