If San Carlos homes now sell for $1,604 a square foot, what should a 2,400-square-foot house on a hillside lot cost? Multiply it out and you get about $3.85 million. That math sends buyers to the wrong conclusion more often than any other number in a listing packet.
The $1,604 figure is real. It's the median price per square foot for single-family homes in San Carlos in September 2026, from the San Mateo County Association of Realtors' September 2026 report, compiled from MLSListings data. A year earlier, in September 2025, the same report showed $1,402. That's a 14% jump in twelve months. For the same two Septembers, though, the average sale price went from $2,890,136 to $2,902,421, a change of less than half a percent.
Prices per foot went up 14% while total prices stayed flat. Most of that gap comes from the size of the homes that sold.
Two Septembers, side by side
SAMCAR's monthly tables include the average size of the homes that sold. Here are the two San Carlos rows.
| San Carlos single-family | September 2025 | September 2026 |
|---|---|---|
| Homes sold | 22 | 19 |
| Average sale price | $2,890,136 | $2,902,421 |
| Median sale price | $2,590,000 | $2,750,000 |
| Median $/sq ft | $1,402 | $1,604 |
| Average home size | 2,097 sq ft | 1,871 sq ft |
| Average lot size | 8,577 sq ft | 8,085 sq ft |
| Sale-to-list | 108% | 108% |
The average home sold in September 2026 was about 11% smaller than the one sold a year before. Buyers paid about the same total for less house, so the per-foot figure rose. Sale-to-list was identical at 108% both months, which means buyers were competing just as hard, not harder.
Nineteen sales is also a small sample. A couple of compact homes near downtown or a single large hillside sale can move a monthly median a long way.
The same swing shows up month after month
September 2026 isn't unusual. Go through SAMCAR's monthly San Carlos rows for 2025 and 2026 and price per square foot keeps moving opposite to average home size:
- March 2025: $1,639 per sq ft, the highest of the 21 months, when the average home sold was 1,747 sq ft, the smallest of the 20 months that report a size.
- January 2026: $1,176 per sq ft, the lowest of the period, with an average home of 2,254 sq ft.
- March 2026: $1,370 per sq ft, yet the median sale price was $3,167,500 and the average home was 2,599 sq ft, the largest of the period.
- June 2026: $1,579 per sq ft with an average home of 1,910 sq ft.
March 2026 is the clearest case. It had the highest median sale price of the year and one of the lower per-foot figures, because the homes were big. The pattern isn't perfect. February 2025 posted $1,581 per sq ft on a 2,257 sq ft average. Still, the direction holds far more often than not.
The Federal Reserve Bank of St. Louis notes that when median prices move, "observed changes could be due to changes in the composition of homes sold as opposed to changes due to market conditions." The FHFA makes the same distinction about its own index: simple measures "reflect changes in both the prices and the composition or quantity of housing." A monthly San Carlos median reflects which 19 or 25 houses happened to close that month.
Why a smaller San Carlos house costs more per foot
Part of the reason is land. A San Carlos lot holds a large share of a property's value, and that value doesn't shrink just because the house on it is modest. Split the price by square footage and a 1,500-square-foot ranch on a standard lot carries more land cost per foot than a 2,600-square-foot remodel does.
Research backs up the land side. A UC Riverside economics paper finds that "the value of a land parcel increases less than proportionally with the size of the lot," so "the price per square foot of a lot decreases as lot size increases." A Urban Land Institute study of established Boise neighborhoods describes smaller older houses "generally resulting in lower sales prices but higher prices per square foot, particularly in the more desirable locations." That's a different market, but the setup is familiar to anyone who has watched an original ranch house sell on a quiet San Carlos street.
San Carlos sales sat on lots averaging 7,879 sq ft in Q3 2026, compared with 7,546 in Belmont and 7,592 in Redwood City. When smaller homes on those lots make up more of a month's sales, the per-foot figure climbs even if no individual buyer paid more than last year.
Belmont looks cheaper per foot than it is
The composition effect also skews city comparisons, and that's where it does the most damage to a buyer's planning. In September 2026, Belmont's median sale price was $2,715,000, close to San Carlos's $2,750,000. Belmont's median price per square foot was $1,261, with an average home of 2,135 sq ft. Comparing those two Septembers, San Carlos looks 27% more expensive per foot at nearly the same total price.
Use the full quarter instead and the gap is about half that size.
| Q3 2026 single-family | San Carlos | Belmont | Redwood City |
|---|---|---|---|
| Homes sold | 70 | 48 | 137 |
| Median sale price | $2,651,000 | $2,437,500 | $2,400,000 |
| Median $/sq ft | $1,449 | $1,276 | $1,309 |
| Average home size | 2,030 sq ft | 2,099 sq ft | 1,953 sq ft |
| Sale-to-list | 108% | 105% | 106% |
With average home sizes close together, San Carlos ran about 14% above Belmont and about 11% above Redwood City per foot in Q3 2026. That's a real premium, and it's well short of what the September snapshot suggests. A buyer who budgets off the single-month gap will overestimate how much more house the same money buys across the city line.
The market held still. Supply didn't.
Over a longer window, value per foot in San Carlos has barely moved. SAMCAR's Q3 2026 report, published October 9, put the San Carlos median at $2,651,000 and $1,449 per square foot. For all of 2025, the annual report showed $2,650,000 and $1,415. The median is $1,000 apart and per-foot is up about 2.4%.
The number of sellers did change. San Carlos had 16 new listings in September 2026, compared with 35 in September 2025. For the quarter, Q3 2026 brought 64 new listings, while July through September 2025 brought 79 combined. Both quarters closed 70 sales. Demand stayed level, fewer homes came to market, and months of inventory sat at 0.8 in Q3 2026.
The next two months are usually the thinnest of the year. In November 2025, San Carlos added 11 new single-family listings. In December 2025, it added 6. With so few sales, a single closing can swing the monthly per-foot figure by a lot, so anyone shopping this winter will be reading the noisiest numbers of the year.
Putting the number to work on a real listing
Appraisers don't apply a citywide per-foot figure to a house, and buyers shouldn't either. The Fannie Mae Selling Guide tells appraisers to pick comparables with similar "site, room count, finished area, style, and condition." Its guidance on adjustments specifically warns against a per-square-foot adjustment "based on a rule-of-thumb" when the market shows a different number. Here's how I use the numbers in practice:
- Compare homes of similar size. A 1,700-square-foot house should be judged against other 1,700-square-foot sales, not the citywide median.
- Use quarters or full years, not months. Q3 2026's $1,449 is a far steadier baseline than September's $1,604.
- Look at average home size before reading per-foot. If the homes got smaller, the per-foot number will probably rise with them.
- Remember the lot. A small house on a standard San Carlos lot will show a high per-foot price, and much of that reflects the land under it.
- Watch new listings more than prices this winter. The supply drop is the trend these reports actually confirm.
A few questions I'm getting
Did San Carlos home values really rise 14% this year? The September per-foot figure did. The Q3 2026 median sale price is essentially the same as the 2025 annual median, and per-foot is up about 2.4% over the same comparison.
Is San Carlos more expensive than Belmont? Per foot, yes, by about 14% in Q3 2026 when home sizes were similar. September alone suggests 27%, and that wider gap is mostly the difference in home sizes.
When will October numbers be out? SAMCAR published the September and Q3 reports on October 9. October's figures should show the first signs of the usual seasonal drop in listings.
If you're looking at a San Carlos home this winter and want to know what it's worth per foot against houses that are actually comparable to it, I'll pull those sales and walk you through them line by line. Call Bob, or start at Bob Bredel - Main Site.
