What Counts as Square Footage? A Marin County Guide to Verifying Home Size

When buying or selling a home in Marin County, one of the most commonly cited — and most misunderstood — data points is square footage. It plays a major role in pricing, value perception, and buyer decision-making, yet it’s rarely as precise as people assume.

The reality: there is no single universally “correct” square footage number for most homes.

Let’s break down what actually counts, where these numbers come from, and what buyers should pay attention to.

The Most Common Sources of Square Footage

In nearly every listing, square footage is pulled from one (or more) of the following sources:

1. Property Tax Records

This is often the default number used in listings. However, tax records can be outdated or inaccurate — especially if improvements, additions, or remodels were done without updates being reported.

Key takeaway:
Tax records are easy to access, but not always reliable.

2. Recent Appraisals

Licensed appraisers typically measure the home themselves as part of the appraisal process. They often follow standardized guidelines when calculating square footage.

Why this matters:
Appraisals are generally one of the more credible sources — but even they can vary slightly depending on methodology.

3. Floor Plans by Graphic Artists

Many listings today include professionally measured floor plans created by third-party companies. These are typically based on interior measurements and are used for marketing purposes.

Important note:
These measurements are helpful for visualizing layout and flow, but they are still considered approximate.

4. As-Builts or Architectural Plans

Original plans or updated “as-built” drawings can show the intended or existing layout of the home.

The catch:
Plans don’t always reflect what was actually constructed — or what exists today after years of changes.

Why No Two Measurements Match Exactly

Here’s the part that surprises most buyers and sellers:

👉 It’s completely normal for square footage numbers to differ — sometimes meaningfully — across sources.

Why?

• Different measurement standards (interior vs. exterior walls)
• Inclusion or exclusion of stairwells, hallways, or storage areas
• Human error or interpretation
• Changes to the home over time

Even highly qualified professionals can come up with slightly different numbers for the same property.

The Gray Areas: What “Counts” as Square Footage?

Not all space is treated equally — and this is where things can get a bit subjective.

Common Exclusions

• Garages are typically not included in marketed square footage
• Unfinished basements or storage areas may be excluded

Common Inclusions (Sometimes)

• “Bonus rooms”
• Converted spaces
• Unpermitted but livable areas

In many cases, if a space is habitable and functional, it may be included in the marketed square footage — even if it doesn’t strictly meet permitting standards.

This creates a gray area that varies from listing to listing.

What Buyers Should Do

Given all of this variability, there’s one clear best practice:

👉 Buyers should independently verify square footage to their own satisfaction.

That might include:

• Reviewing multiple sources (tax records, disclosures, appraisal if available)
• Hiring a professional to measure the home
• Evaluating how the space actually lives, not just the number on paper

The Bottom Line

Square footage is an important metric — but it’s not an exact science.

• Multiple sources often exist
• Numbers frequently vary
• Some spaces fall into gray areas

At the end of the day, how a home feels, functions, and fits your needs is just as important — if not more — than the exact square footage figure.

Final Thought

In Marin County real estate, the most informed buyers understand this nuance. They don’t rely on a single number — they look at the full picture.

If you ever have questions about how square footage is being represented in a specific property, it’s worth digging deeper. That extra diligence can make a meaningful difference in how you evaluate value.