Accuracy · 4 min read

Why Does My PlanSnapper Measurement Differ from the County Assessor or MLS?

If your PlanSnapper measurement does not match what the county assessor or MLS shows, that is not necessarily a problem. There are several legitimate reasons for differences, and PlanSnapper is often the more reliable number.

County assessor data is frequently outdated

Assessor records are updated when permits are pulled and occasionally during reassessment cycles. They are not updated every time a room is finished, an addition is built, or a measurement is corrected. A property that had an addition ten years ago may still show the pre-addition square footage in county records if the addition was unpermitted or the assessor never updated the file.

Many counties also used permit records or rough exterior measurements to establish the original square footage. These are not always accurate, and errors persist for decades.

MLS square footage is often self-reported

In most markets, the seller or listing agent enters the square footage into the MLS. It may come from the county assessor, from a previous appraisal, from a rough estimate, or from a measurement method that includes spaces that would not count as GLA under ANSI Z765. There is no standard verification process before a listing goes live.

MLS figures can be off by hundreds of square feet, sometimes more. This is a well-documented issue in real estate.

GLA definitions vary by source

Some sources include finished basement area in the square footage total. Others include garages, sunrooms, or partially finished spaces. The ANSI Z765 standard used for GLA specifically excludes below-grade areas regardless of finish level, but not every data source follows that standard.

PlanSnapper measures the perimeter you define. If you upload a main floor plan and measure it, that is what you get. If your measurement is smaller than the assessor figure, it is worth asking whether the assessor included the basement.

PlanSnapper measures what is actually on the floor plan

PlanSnapper does not rely on public records or self-reported data. It measures the floor plan image you provide. If that floor plan is accurate (from CubiCasa, Matterport, iGUIDE, or a proper appraisal sketch), the PlanSnapper measurement reflects the actual floor plan dimensions.

That is often more reliable than what is on record. Real estate appraisers use PlanSnapper precisely because it gives them a number grounded in the actual floor plan, not in whatever the county has on file.

When to dig deeper

A significant difference (more than 5%) between PlanSnapper and the assessor or MLS is worth investigating. Common explanations:

• Unpermitted addition not reflected in county records
• Finished basement included in one number but not the other
• Wrong floor plan uploaded (different level or outdated plan)
• Scale set incorrectly in PlanSnapper (double-check your scale wall)
• Assessor figure was never updated after a renovation

Learn more

Why County Assessor Square Footage Is Often Wrong and How Accurate Is MLS Square Footage?