Every ZIP code,
with the data behind it

A ZIP code is a five-digit number used by the United States Postal Service to route mail. The name is an acronym for Zone Improvement Plan, introduced in 1963 when rising mail volumes made manual sorting impractical. Each code corresponds to a set of delivery routes served by a particular post office, and the digits narrow geographically from left to right — the first identifies a broad group of states, the first three a regional sorting facility, and the last two the specific delivery area.

The critical thing to understand, and the source of most confusion about ZIP code data, is that a ZIP code is not a shape. It is a collection of lines along streets. The Postal Service never drew boundaries around them, because it never needed to — a carrier walks a route, and the route is the code. Every map you have ever seen showing ZIP code areas is an approximation drawn by somebody else after the fact.

Why that matters for the numbers on this site

Because ZIP codes have no official area, the Census Bureau cannot publish statistics for them directly. Instead it publishes for ZIP Code Tabulation Areas, or ZCTAs — polygons built by assigning each census block to whichever ZIP code is most common among the addresses inside it. ZCTAs approximate ZIP codes closely enough to be useful, but they are not identical, and there are fewer of them: roughly 33,600 ZCTAs against about 41,700 postal codes.

The gap is not an error. Around 7,848 US postal codes have no residential population at all. Some serve only PO Boxes at a particular post office. Others are assigned to a single high-volume recipient — a corporation, a university mailroom, a government agency. Nobody lives at these addresses, so there is nothing for the Census to measure. When you see a ZIP code site reporting a population of zero for one of these, that is a formatting failure, not a fact. We label them for what they are instead.

A postal code lookup is most often used to answer a narrow question — what code covers this address, or what city does this code belong to. But because so much public data is published at this level, a good lookup answers considerably more than that.

Before you move somewhere

Median household income, median home value, median rent, the split between owners and renters, the age profile, educational attainment and typical commute time together give a fair picture of what an area is like to live in. Four figures — population, median income, degree attainment and unemployment rate — answer more relocation questions than most neighbourhood guides manage in several thousand words.

Before you open a business

Site selection depends on who is nearby and what they can spend. Population density tells you foot traffic potential. Income distribution tells you what price points will work. Age bands tell you which products fit. Commute patterns tell you whether people are around during the day.

When you are comparing options

Absolute numbers mean little without context, which is why every profile on this site includes a national percentile. Knowing that a ZIP code's median income is $94,000 is less useful than knowing it ranks ahead of 78% of American postal codes. We publish both.

When you need to check a claim

Every figure on every page cites the exact Census table it came from, along with the survey vintage. Where a margin of error exists, we print it. If our number differs from another source, you can identify why in a couple of minutes rather than guessing.

Estimates, not counts

American Community Survey figures come from a rolling sample, not a headcount. The 5-Year estimates pool sixty months of responses to produce numbers reliable enough for small areas. Every estimate carries a margin of error at 90% confidence, meaning the true value has a nine in ten chance of falling within that range. For a large postal code the margin is usually small relative to the estimate. For a small one it can be substantial — occasionally larger than the estimate itself. We display it so you can judge.

Medians, not averages

Where we report income or home value we use the median: the midpoint, with half of households above and half below. Averages are distorted by extremes, and in areas with a small number of very high earners a mean income can describe almost nobody. The median is the more honest summary.

Direction over precision

For small postal codes, treat the direction of a figure as more reliable than its exact value. That a ZIP code is markedly wealthier than the national median is a robust finding; that its median income is precisely $118,400 rather than $115,000 usually is not.

A postal code is not a neighbourhood

Codes can span several distinct neighbourhoods with quite different characters, and a single neighbourhood can be split across several codes. A ZIP-level median flattens that variation. It is a useful summary, not a description of every street.

Each of the 41,488 profiles carries roughly 250 data points, drawn from 21 American Community Survey tables plus Census geography files. Specifically:

• People — total population with margin of error, median age, full age distribution, race and ethnicity, household composition and average household size
• Income and work — median household income, per capita income, the full income distribution across seven brackets, poverty rate, labor force participation, unemployment rate, and educational attainment
• Housing — median home value, median gross rent, owner and renter split, units by building type, median year built, total housing units and vacancy rate
• Commuting — mode of transport, travel time distribution and mean one-way commute
• Geography — coordinates, land and water area, population density, time zone, county, and straight-line distance to major cities
• Live data — current conditions and forecast from the National Weather Service, and a running local clock
• Context — national percentile ranks, the eight nearest postal codes, and other codes in the same city and county

Where a figure is suppressed or unavailable, we say so rather than substituting a zero.