How Is Condo Square Footage Measured?

Condos are not measured like houses. Instead of exterior wall-to-wall, condos are typically measured from interior surfaces — which means the same unit can have different square footage depending on who measured it and which method they used. Here is how it works.

Interior measurement vs. exterior measurement

Single-family homes are measured from the exterior walls under ANSI Z765-2021 — the national appraisal standard. Condos are different because you do not own the exterior structure. What you own is the air space (and sometimes the interior surfaces) defined in your condo declaration.

For condos, appraisers typically measure from the interior face of the perimeter walls. This excludes the wall thickness itself. The result is a smaller number than an exterior measurement of the same unit would produce — sometimes by 5–10% depending on wall thickness and construction type.

Three common measurement methods

There is no universal standard for condo measurement the way ANSI Z765 governs single-family homes. In practice, three methods are used:

Interior wall-to-wall: The most common method for appraisals. Measured from the interior face of each bounding wall. Does not include wall thickness, structural columns inside the unit, or shared wall framing.
Drip-line (glass-line): Measured to the exterior face of windows and doors rather than interior drywall. Used in some high-rise markets and floor plan databases. Produces a slightly larger number than strict interior measurement.
Center-line of shared walls: Measures to the centerline of walls shared with neighboring units. Common in some markets and older appraisals. The result falls between interior-only and full exterior.

The method that applies to your unit is usually specified in the condo declaration or the original developer floor plan. When in doubt, check with the HOA or request the original measured drawings.

Why your condo's square footage numbers probably do not agree

It is extremely common for a condo to have three or four different square footage figures floating around:

Developer/HOA records: Often based on original architectural drawings, which may use a different method than field measurement.
County assessor: Uses whatever method the assessor's office adopted, which varies by county. Often based on exterior or a simplified estimate.
MLS listing: Whatever the agent entered, often pulled from county records or the developer without verification.
Appraisal: Based on the appraiser's field measurement using the method appropriate for that market, usually interior wall-to-wall.

Discrepancies of 50–150 sq ft between sources are common. On a per-square-foot basis, this difference can affect the appraised value — which is why buyers in high-priced condo markets sometimes commission their own measurement before closing.

Does balcony or patio square footage count?

No. Balconies, terraces, and patios are not included in GLA regardless of whether they are shown on the floor plan. They may be noted in the appraisal as "additional features" with their own square footage, and they do contribute to value — but they are not added to the living area total.

Same rule applies to a storage unit or parking space assigned to your condo. They are valued separately, not rolled into the unit's GLA.

How to measure your own condo accurately

If you have the builder's floor plan, you can measure it using PlanSnapper. Upload the floor plan image, trace the interior walls of the unit, set the scale from one known wall length, and read the area. This matches the interior wall-to-wall method appraisers use.

Key things to exclude when tracing:

Balconies and exterior decks
Storage areas outside the unit envelope
Utility closets in the common hallway
Any below-grade area (in a garden-level unit)

Interior closets, laundry rooms, and bathrooms all count toward living area as long as they are inside the unit perimeter and have at least 7 ft of ceiling height.

Townhouse condos: a hybrid case

Townhouse-style condos that share walls but not ceilings or floors with neighbors are sometimes measured with the exterior method on non-shared walls and interior (or center-line) on shared walls. The appraiser notes which method was used. If you are in a townhouse condo and the square footage seems lower than expected, this is often why.

Measure your condo from the floor plan

Upload the builder's floor plan and trace the interior walls. PlanSnapper gives you an accurate interior measurement in minutes.

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