Every investor develops a shorthand. Somebody sends you an address and a price and within about four seconds you have decided whether it is worth opening. For most people that shorthand is price per square foot, and for anybody buying small multifamily it is price per unit. Both are fast, both are useful, and both will hand you a confidently wrong answer at least a few times a year if you do not know exactly what they are measuring.
These are screening tools. They are not valuation and they are not underwriting. The distinction sounds pedantic until you have paid for it.
What price per square foot is actually comparing
Price divided by finished square footage. A 180,000 house with 1,400 finished feet is roughly 129 a foot. That is the whole calculation, and its simplicity is the source of both its value and its failure modes.
What it does well is normalize for size inside a tight set. If you are looking at four ranches on the same street built by the same builder in the same decade, price per foot tells you something real about which one is priced aggressively. That is the condition under which the number works: same submarket, same property type, same vintage, same condition.
Change any one of those and the comparison degrades fast. Here is why.
Square footage is not one number. Above grade finished, below grade finished, and total under roof are three different figures and they are not interchangeable. A 1,200 foot ranch with a 900 foot finished basement gets marketed as 2,100 feet and appraises closer to 1,200 above grade with a separate line for the basement. If you compute price per foot on the marketing number and the comps on the appraisal number, you have made two properties look different when they are not, or the reverse. Worse is finished space that was never permitted, which the appraiser may decline to count at all. What happens in that case is covered in unpermitted finished square footage.
Small properties always look expensive per foot. Every property has a fixed cost core: a kitchen, a bathroom, a furnace, a roof, a lot. Spread that across 900 feet and the per foot number is high. Spread it across 2,400 feet and it is low. That is not a pricing signal, it is arithmetic, and it is the single most common way the metric misleads. Comparing a 900 foot bungalow to a 2,400 foot colonial on a per foot basis tells you almost nothing about which is the better buy.
It ignores the land. Two identical houses, one on a quarter acre and one on two acres, produce the same price per foot and very different assets.
It ignores condition entirely. This is the one that costs rehabbers money. A gut job and a turnkey rental with the same footprint at the same price per foot are not the same deal and the difference is the rehab budget. Price per foot with no condition adjustment is how a flip gets bought at a number that never worked.
Price per unit, and why it is the better screen on multifamily
On two to four unit property and above, price per unit does a job price per foot cannot. A triplex at 390,000 is 130,000 a unit. That number is directly comparable across the small multifamily market in a way that square footage is not, because units generate rent and square feet do not.
The reason it works better is that income follows doors. A duplex with two 800 foot units and a duplex with two 1,100 foot units in the same neighborhood rent much closer to each other than their square footage difference would suggest, because a two bedroom is a two bedroom. So the per unit number tracks the thing that actually produces cash flow.
The failures are narrower but real. Unit mix is the big one. Four studios and four three-bedrooms at the same price per unit are not the same building. And price per unit says nothing about condition, deferred maintenance, or whether the units are currently rented at market. Two buildings at 130,000 a unit where one is fully leased at market and the other has three units that have not been touched since the previous owner’s father ran it are different purchases at the same number.
What these numbers cannot see, which is everything that matters to the loan
Here is the fundamental problem with both metrics, and it is worth stating plainly: neither one contains any income. You can compute both from a listing sheet without knowing the rent. That is exactly why they are fast, and exactly why they cannot tell you whether a deal works.
A lender underwriting a rental loan does not care what you paid per foot. The ratio is rent against principal, interest, taxes, insurance and any association dues. Two properties can sit at an identical 129 a foot and land on opposite sides of a 1.20 coverage requirement because one has a tax bill twice the other’s, or sits in a flood zone, or carries an association fee.
Work an example. Two houses, both 180,000, both 1,400 feet, both 129 a foot. House A rents for 1,750 with taxes of 2,900 a year and insurance of 1,100. House B rents for 1,600 with taxes of 5,400 a year and insurance of 1,800 because it needs flood coverage. Same screen. Very different files. On a 135,000 loan, House A clears comfortably and House B may not clear at all, and nothing in the per foot number gave you a hint. The flood piece alone is frequently decisive, as laid out in how flood insurance hits your DSCR.
Run both through the DSCR deal calculator and the difference appears immediately. Run them through a per foot screen and they are twins.
Where these sit among the other shortcuts
Price per foot and price per unit belong to a family of screening metrics, and each one covers a blind spot of the others. Used as a set they are genuinely useful. Used individually they are how people talk themselves into deals.
The gross rent multiplier is the closest relative and the most useful companion, because it is the first metric in the family that contains income. Price divided by annual gross rent. It fixes the central blind spot of the per foot number while inheriting its own, since it ignores expenses entirely.
Cap rate goes one layer deeper by subtracting operating expenses, which is why GRM and cap rate disagree in a predictable direction: the gap between them is the expense load, and a property with a high tax bill will look fine on GRM and poor on cap rate. Cap rate then has its own blind spot, since it ignores financing, which is the point of cap rate versus DSCR.
The 1 percent rule is the same idea as GRM expressed monthly. The 50 percent rule and the operating expense ratio attack the expense side that GRM ignores. Break-even occupancy and break-even rent tell you how much room you have before it stops working, which is the question all the others dodge. And IRR and equity multiple are the only ones that account for time.
The honest hierarchy runs like this. Price per foot and price per unit screen. GRM filters. Cap rate and break-even analyze. DSCR is what the lender uses to decide. Cash on cash and IRR tell you whether it was worth doing. Using a screen where an analysis belongs is the error, and it is a very common one.
How to actually use them
Build your own per foot and per unit baselines by submarket and refresh them a couple of times a year. Not citywide, not countywide. Neighborhood by neighborhood, because the variance inside a single zip code will be larger than the variance between two cities. Once you have a baseline, the number does the one job it is good at: it tells you when something is far enough off the baseline to be worth a look.
Then treat anything unusually cheap per foot as a question, not an answer. Genuinely low per foot numbers usually have a cause. Functional obsolescence, a three bedroom with one bathroom, a floor plan that requires walking through a bedroom. Deferred capital, a roof at the end of its life, which can reprice a finished file all by itself as described in roof age and your rental loan. A location issue that does not appear in the photographs. An environmental item. Sometimes there is no cause and it is genuinely mispriced, which is the whole business, but the base rate on that is lower than optimism suggests.
And never, ever, use price per foot to set an offer on a rehab. The correct tool for that is after repair value less the rehab budget less your required margin, and if you are working from a per foot number on a house that needs eighty thousand dollars of work, you are pricing a property that does not exist yet with a metric that cannot see the difference.
The short version
Price per square foot answers one question well: is this priced in line with very similar properties nearby. Price per unit answers the same question on small multifamily and answers it better, because doors correlate with income and feet do not.
Neither one contains rent, expenses, taxes, insurance, condition, or debt. Every one of those is between you and a working deal, and every one of them shows up in underwriting whether or not you looked at it first.
Screen with them. Decide with the ratio. If you have a property that screens well and you want to know whether it finances, send us the numbers and we will run it against real program parameters rather than a rule of thumb.
Program requirements, coverage ratio minimums, appraisal standards for measuring gross living area, and how any given lender treats below grade space vary by lender and by product and are subject to change. Anything in this article involving tax treatment or property assessment should be confirmed with your accountant, and anything involving permitting, zoning, or unpermitted space should be reviewed with a licensed attorney or a licensed code professional in the property’s jurisdiction before you rely on it.
FMC Capital is a Pittsburgh-based mortgage brokerage financing investment property for real estate investors across Pennsylvania and additional states. NMLS #1840537.
This article is for general information only and is not legal, tax, or investment advice. Loan terms, program guidelines, and applicable law vary and are subject to change. FMC Capital, NMLS #1840537. Equal Housing Opportunity.