Guides · Floor Plan Measurement
For real estate investors, square footage affects every part of underwriting: acquisition price, rent potential, and ARV comparable adjustments. Relying on MLS or county records introduces errors that compound throughout your analysis. Here's how to verify sq ft on acquisition targets fast.
MLS square footage is agent-reported and often includes basement space, unheated areas, or spaces that won't count in an appraisal. Example: target listed at 2,800 sq ft. Comps sell at $150/sq ft. ARV model says $420,000. But actual above-grade GLA is 2,200 sq ft: the rest is finished basement. Appraiser uses $150/sq ft for above-grade and $90/sq ft for below-grade. True ARV = (2,200 × $150) + (600 × $90) = $330,000 + $54,000 = $384,000. That's $36,000 less than the model. The difference between a deal and a loss.
1. From the MLS listing, download or screenshot the floor plan. Most listings now include a CubiCasa, Matterport, or sketched floor plan. 2. Upload to MeasureFloorPlan.com. 3. Trace above-grade living area only. Draw garage and basement as separate polygons if present. 4. Set scale from any labeled dimension. 5. Record: above-grade GLA, basement finished area (if any), garage (if any). 6. Apply appropriate $/sq ft rates for each area type in your underwriting model.
For deals where you're comparing multiple properties: spend 5 minutes per property measuring each one. Build a spreadsheet: address, above-grade GLA, below-grade finished area, garage area. Now you have consistent, independently-verified measurements across your entire comp set: not a mix of agent-reported numbers using different inclusion criteria. Your $/sq ft analysis is based on apples-to-apples comparisons.
Identifying a square footage problem during initial screening (5 minutes) is far better than discovering it after LOI, after inspection, or after the appraisal comes in. Measuring the floor plan is one of the highest-ROI checks in your pre-offer diligence workflow.
Ready to measure your floor plan?
Upload your floor plan and trace square footage in any browser: no software required.
Start Measuring →Why verify square footage on a rental investment property?
MLS square footage is wrong roughly 30 percent of the time, often by 5 to 10 percent. On a $200,000 underwriting model that's a $10,000 to $20,000 valuation error. Verifying before you bid prevents overpaying and surfaces hidden value (unrecorded additions).
How fast is the verification workflow for multiple comps?
Each verification takes about two minutes once you have the floor plan. For ten comps, budget 20 minutes. Far less than walking each property, and much more accurate than trusting MLS data.
Where do I get the floor plan for an off-market property?
Try the county assessor's GIS portal, the MLS history, prior listing photos, or order a CubiCasa or Matterport scan during inspection. For off-market wholesale deals, asking the seller directly often works.
Does this give me appraisal-grade GLA?
Yes, when the trace follows ANSI Z765 (above-grade finished only, exterior measurement). The result is the same methodology a licensed appraiser would use, calculated from the same floor plan.
Can I use this for cap rate calculations?
Yes. Verified square footage feeds into per-square-foot rent comparisons, replacement cost, and price-per-square-foot underwriting. All three become unreliable when the underlying square footage is wrong.