How this instrument works
A comparable price per square foot is the recent sale price of similar nearby homes divided by their square footage, averaged across several truly comparable sales rather than pulled from a single listing. Multiplying that rate by a subject home's own square footage produces a baseline estimate — the sales comparison approach that underlies both a real estate agent's CMA and a formal appraisal, just without the walkthrough, the photographs, or the line-by-line adjustments a licensed appraiser documents.
Homeowners reach for this math before listing a house for sale, before applying for a home equity line of credit, or when checking whether rising local prices have pushed a mortgage below the 80% loan-to-value threshold that ends private mortgage insurance. Agents run a rougher version of the same arithmetic during a listing consultation, gathering three or four recent nearby sales and averaging their price per square foot before a formal CMA report gets typed up.
The formula is only as sound as the comparables feeding it, and its single blind spot is size itself: larger homes routinely sell at a lower price per square foot than smaller ones nearby, because land, kitchens, and bathrooms do not scale linearly with square footage. Pulling a rate from a 1,200 sq ft comp and applying it unadjusted to a 3,000 sq ft subject home overstates value; the condition adjustment here is one blunt percentage, not the room-by-room grid of adjustments a licensed appraiser fills out for lot size, garage, extra bathrooms, or a pool.
- Enter the going rate in Comparable price per sq ft, $ — averaged from a few recent, genuinely similar nearby sales.
- Enter the subject home's own footprint in Home size, sq ft.
- Set Condition adjustment, % (+/-) to nudge the estimate up for recent renovations or down for deferred maintenance versus the comps.
- Read Estimated home value — the comparable-sales estimate the three inputs imply.
- Re-run with a tighter or wider comp set to see how much the price-per-square-foot assumption alone moves the result.
Worked example — 1,800 sq ft at $250 per foot
Set Comparable price per sq ft, $ to 250, Home size, sq ft to 1,800, and Condition adjustment, % (+/-) to 0. The instrument multiplies 250 by 1,800 to get 450,000, and with no adjustment applied Estimated home value reads exactly $450,000 — the same comparable-sales math a real estate agent's CMA runs from a handful of recent nearby closings, minus the human judgment about this specific property's actual condition, layout, and lot that a full appraisal or agent walkthrough would add.
Nudge the condition adjustment and the same comps move the estimate directly: a -10% adjustment for a home needing visible updating against its comparables drops the figure to $405,000, while a +10% adjustment for recent renovations or premium finishes lifts it to $495,000. Ninety thousand dollars separates those two figures on an identical $250/sqft, 1,800 sq ft input — condition judgment, not the comparable rate, is doing that work.
Questions
What counts as a genuinely comparable sale?
A home similar in age, size, style, and location that sold recently — typically within the last three to six months and within a mile or so, adjusted for how fast the local market is moving. Pulling a price per square foot from a different neighborhood, an older sale, or a materially larger or smaller home undermines the estimate before the multiplication even starts.
Why do larger homes often show a lower price per square foot?
Because land, kitchens, and bathrooms do not scale in proportion to floor area — a 3,000 sq ft home typically needs one kitchen and two or three bathrooms, much like a 2,000 sq ft home, so those fixed-cost rooms get spread over more square footage. Applying a small comp's rate to a much larger home, or the reverse, is the single most common misreading of this arithmetic.
How is this different from a home affordability calculator?
A home affordability calculator works from a buyer's income to estimate what price they might qualify to pay. This calculator works from recent comparable sales to estimate what a specific property is actually worth today — a seller's or owner's question, not a buyer's, and the two figures have no reason to match.
How is this different from ARV for house flippers?
ARV, or after repair value, forecasts what a property will be worth once a renovation is finished, built from comps of already-renovated homes. This calculator estimates a property's value in its current condition, using comps of homes similar to how it stands right now — the condition adjustment nudges a percentage, it does not model a finished renovation.
Does the condition adjustment replace a real appraisal?
No. A licensed appraiser itemizes separate dollar adjustments for lot size, garage space, extra bedrooms and bathrooms, a pool, and dozens of other line items, then reconciles three or more comparable sales into a single opinion of value. This calculator compresses all of that into one percentage nudge — useful for a fast estimate, not a substitute for the appraisal a lender will actually require.
Why might my estimate differ from a real estate agent's number?
Agents typically pull more comparable sales, weight the most recent and most similar ones more heavily, and adjust for specific features this formula folds into a single condition percentage — a finished basement, an updated kitchen, a corner lot. A wide gap usually means the comparable price per square foot entered here came from a smaller, less carefully matched set of sales than an agent's CMA would use.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.