State Plane coordinates are flat x and y coordinates, called easting and northing, on a grid designed for each US state. Each state is split into one or more zones, and each zone has its own projection and its own origin, so a point is given in feet or meters from that origin. The Colorado State Capitol, for example, sits at E 3,144,869.01 ft, N 1,694,557.20 ft in Colorado Central (zone 0502). Google Maps can’t read them, so to find a State Plane point on a map you convert it to latitude and longitude first. Here’s how the system works, how to read it and how to convert it.
What State Plane coordinates are
The State Plane Coordinate System of 1983 (SPCS 83) sits on the NAD 83 datum. Its goal is practical: on a small enough zone, the flat grid is so close to the real ground that surveyors and engineers can measure in plain feet, with no curvature math.
In the converter’s data, which comes from the EPSG registry, there are 124 zones:
- 12 states and Puerto Rico have a single zone, among them Connecticut, Maryland, Montana, New Jersey, North Carolina and Tennessee.
- Others have several: Alaska 10, California 6, Hawaii 5 and Texas 5; Colorado, Arizona and Florida have 3 each.
- Zones that run north to south use a Transverse Mercator projection (54 zones); zones that run east to west, a Lambert conformal conic (69). The panhandle of Alaska uses an oblique Mercator, the only one of its kind.
Zone boundaries follow county lines, so the county tells you the zone. Kentucky is a special case: besides its North and South zones, it has a single statewide zone.
How to read a State Plane coordinate
Take the three examples this guide’s converter opens with:
| Point | Zone | Easting | Northing | Unit |
|---|---|---|---|---|
| Colorado State Capitol | Colorado Central (0502) | 3,144,869.01 | 1,694,557.20 | US survey feet |
| Statue of Liberty | New York Long Island (3104) | 971,908.46 | 190,390.84 | US survey feet |
| Phoenix (Census center point) | Arizona Central (0202) | 647,175.61 | 935,764.84 | international feet |
- The easting (E or X) is the distance east of the zone’s origin, and the northing (N or Y) the distance north of it.
- Each zone adds a false easting (and sometimes a false northing) so that every coordinate in it is positive.
- A coordinate means nothing without its zone and its unit. The same numbers exist in every zone of every state.
The same Capitol point in meters is E 958,557.99 m and N 516,502.07 m, so always check the unit on the drawing, plat or data file.
US survey feet or international feet?
There are two feet, and the difference matters at State Plane scale:
- The US survey foot is 1200/3937 m, about 0.3048006 m.
- The international foot is exactly 0.3048 m.
They differ by about 2 parts per million. That sounds tiny, but State Plane eastings run into the millions: the Capitol’s 958,557.99 m are 3,144,869.01 US survey feet and 3,144,875.3 international feet, a 6.3 ft difference. Mix up the units and your point moves by a car length.
According to the NIST, the US survey foot has been obsolete since January 1, 2023, superseded by the international foot. Data made before then, and many zones in the EPSG registry, still use it. In the converter’s data, Arizona, Michigan, Montana, North Dakota, Oregon and South Carolina use international feet, Utah has both, and the rest use US survey feet. Every result also comes in meters.
How to find your zone
The easiest way is to let the converter find it from the county:
- Open the national grid converter.
- In From, choose latitude and longitude; in To, choose State Plane (NAD83).
- Paste your coordinates, one pair per line, with a name first if you like. Leave the zone on automatic.
- Each result shows its zone and code, its EPSG number, its unit and the county it falls in.
The Statue of Liberty, for example, comes back as New York Long Island (3104), New York County. If you don’t know your point’s latitude and longitude, get them from Google Maps with the guide to Google Maps coordinates.
Convert State Plane to latitude and longitude
To put a State Plane point on Google Maps:
- In the converter, choose State Plane (NAD83) in From and pick the zone and the unit (US survey feet, international feet or meters).
- Choose Latitude and longitude in To.
- Paste the easting and northing, one point per line.
- Copy the result and paste it into Google Maps’ search box: latitude first, with a decimal point, as Google’s help asks.
The converter matches PROJ and the NGS’s own tool to the millimeter for the projection. The datum is where the error comes in: like PROJ by default, it treats NAD 83 as WGS 84, and today the two are 1 to 2 m (3 to 7 ft) apart in the lower 48. That’s fine for mapping and GIS. For boundary or construction work, use the NGS’s NCAT with a proper NAD 83 (2011) transformation, or ask a surveyor.
What’s next: SPCS2022
The NGS is preparing the State Plane Coordinate System of 2022, tied to the new 2022 reference frames that will replace NAD 83. On its beta site (updated May 14, 2026), SPCS2022 has up to three zone layers per state, with a statewide zone for every state and territory. According to the NGS’s new datums FAQ, the vote to approve the modernized system is likely in mid 2027, and until then the current system stays official. For now, SPCS 83 on NAD 83 is the State Plane system in official use.
If you work with UTM instead, the UTM guide explains zones, bands and datums the same way.