This state plane coordinate converter moves between NAD83 State Plane coordinates and latitude and longitude, in both directions. Choose your state and zone, enter an easting and northing in metres, US survey feet or international feet, and get the latitude and longitude back — or paste a lat long and read the zone coordinates. All 134 NAD83 State Plane zones across the 50 states are built in, and the projection mathematics agrees with the EPSG reference implementation to better than 0.05 mm. Free, in your browser, no login and no upload.
Latitude and longitude in decimal degrees, or as DMS such as 38 12 00 N. West and
south are negative. Need DMS instead? Use the decimal degrees to DMS converter.
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A State Plane coordinate is a projected grid coordinate, so converting it to latitude and longitude means undoing the projection that produced it. Two projections are in use, and the zone you choose decides which one applies.
Lambert Conformal Conic (2SP) zones, used for bands that run mainly east-west, are defined
by two standard parallels. The cone constant is
n = ln(m₁ / m₂) ÷ ln(t₁ / t₂), where
m = cos φ ÷ √(1 − e² sin²φ) and the isometric function is
t = tan(45° − φ/2) ÷ ((1 − e sinφ) ÷ (1 + e sinφ))^(e/2). The radius to a point is
ρ = a F tⁿ with F = m₁ ÷ (n t₁ⁿ), and the grid coordinates follow from
E = E₀ + ρ sin θ and N = N₀ + ρ₀ − ρ cos θ, where
θ = n (λ − λ₀).
Transverse Mercator zones, used for bands that run mainly north-south, are defined by a
central meridian with a scale factor slightly below one — usually 0.9999, and
0.9996 in Alaska — so that the grid stays close to true ground distance across the
width of the zone. The easting and northing come from the Snyder series in terms of meridian arc
M and the difference in longitude from the central meridian.
Going the other way — state plane to lat long — the tool computes the footpoint latitude by
inverting the meridian arc, then applies the inverse series, or for Lambert zones inverts the
polar equation iteratively. Both paths use the GRS80 ellipsoid
(a = 6,378,137 m, 1/f = 298.257222101), which is the ellipsoid of NAD83.
The State Plane Coordinate System was created in the 1930s because a flat grid is far easier to compute with than latitude and longitude. Each state — and each zone within a large state — is given its own projected plane, chosen so that the distortion introduced by flattening the Earth stays inside a stated tolerance. The original design target was an error no worse than about one part in 10,000, which is roughly 0.1 foot per 1,000 feet inside a zone.
To hold that tolerance, states were split into zones. Narrow zones extending north-south use the Transverse Mercator projection, because a transverse cylinder can be kept close to the ellipsoid along a meridian. Wide zones extending east-west use the Lambert Conformal Conic, because a cone fits a band of latitude closely. Where a state is both wide and tall it gets several zones — Texas has five, California has six, Alaska has ten — and a point is transformed in whichever zone it belongs to.
Every zone is defined by a small set of parameters: the latitude and longitude of the projection origin, the standard parallels or the central-meridian scale factor, and a false easting and northing. The false values exist only to keep every coordinate in the zone positive, and they are chosen so that the numbers stay short and unambiguous — which is why so many zones have a false easting of exactly 500,000 m or 2,000,000 m.
Of the 134 NAD83 zones built into this converter, 74 are Lambert Conformal Conic and 60 are Transverse Mercator. The split follows geography rather than administration.
| Projection | Zone shape | Typical zones | Defined by |
|---|---|---|---|
| Lambert Conformal Conic (2SP) | Wide, running east-west | Texas North / Central / South Central; California zone 1–6 in part; Kansas, Nebraska, Iowa, the Dakotas, Montana, Washington | Two standard parallels plus a false origin |
| Transverse Mercator | Narrow, running north-south | Alaska zone 1–10; Arizona East / Central / West; Illinois East / West; Indiana East / West; most of the eastern seaboard | Central meridian plus a scale factor (0.9999, or 0.9996 in Alaska) |
The choice has a practical consequence. In a Lambert zone, the scale error grows with distance north and south of the standard parallels, and in a Transverse Mercator zone it grows with distance east and west from the central meridian. That is why a coordinate transformed in the wrong zone still returns a latitude and longitude, but one carrying an error that grows the further the point sits from the zone that should have been used. If a point lies close to a zone boundary, use the zone the point is listed in, and record which zone the coordinate belongs to — a state plane coordinate without its zone is not a complete coordinate.
The projection is the same whichever unit you choose; only the numbers change. State Plane coordinate definitions exist in metres and in feet, and the feet versions are simply the metre definitions restated, so a conversion is a fixed scale factor.
The trap is that there are two feet. Until 1 January 2023, State Plane coordinates were commonly
published in US survey feet, where one foot is 1200 ÷ 3937 = 0.304800609601219 m.
Since the survey foot was deprecated, current work uses metres or international feet, where
one foot is exactly 0.3048 m. The difference is about two parts per million, which is
0.0106 ft — about 3.2 mm — per mile. Over a long baseline, a coordinate read in the wrong foot is
metres away from where it should be, and it will look entirely plausible at a glance.
Choose the unit from the record, not from habit. If a plan from the 1990s says feet without qualification, it almost certainly means US survey feet; if a plan from this year says feet, it almost certainly means international feet. Because the same zone has both a metre and a survey foot EPSG code, checking the EPSG code on the source data is the reliable way to settle it.
Take a point in the Kentucky North zone (EPSG:2205), whose standard parallels are 37°58′ and 38°58′ with a false origin at 37°30′ N, 84°15′ W and a false easting of 500,000 m. The point 38.200000° N, 84.500000° W returns an easting of 478,102.274 m and a northing of 77,727.277 m. Because this zone is defined in metres, the same point in US survey feet is 1,568,573.877 ftUS easting — the metre value multiplied by 3937 ÷ 1200.
A useful check on any state plane coordinate is that the northing should be positive and of the order of the distance from the zone's latitude of origin, and the easting should sit within a few hundred kilometres of the false easting. If an easting comes back far from the false easting, or a northing is negative in a zone that should have none, you are almost certainly in the wrong zone or the wrong unit.
This converter covers all 134 NAD83 State Plane zones in the 50 states — every zone defined with the Lambert Conformal Conic (2SP) or Transverse Mercator projection. Two groups are deliberately not included: the Albers Equal Area statewide systems such as Alaska Albers and Hawaii Albers, which are mapping grids rather than State Plane zones, and the Michigan GeoRef Oblique Mercator zone, which uses a different projection formulation and is not a classic State Plane zone.
Accuracy was checked by comparing the implementation against the EPSG reference definitions on test points spread across both projection types and several states. The largest disagreement found was 0.017 mm forward and 0.046 mm inverse — far below the precision of any survey, and below the rounding of the coordinates you are likely to be reading. In other words, the arithmetic is not the limiting factor: your input precision, and the datum and epoch of the source coordinates, are.
One limitation is worth stating plainly. This converter works on NAD83. A coordinate in NAD27 can differ from its NAD83 counterpart by up to about 100 metres, and that difference is a datum transformation, not a projection problem — it cannot be fixed by choosing another zone. If your source is NAD27, that transformation has to happen first.
Apply the inverse of the zone's projection to the easting and northing: subtract the false easting and northing to get offsets from the projection origin, convert those back to a radius or meridian distance on the ellipsoid, then solve for the latitude and longitude. A state plane coordinate converter does the same thing, and the zone must be stated, because the same numbers mean different places in different zones.
Zones are defined by state and, in larger states, by a regional split. Pick the state first, then the zone that contains your work area. If you are near a boundary, use the zone in which your point is listed — and always record the zone alongside the coordinate.
Use what the record says. Legacy State Plane coordinates are normally US survey feet (1200/3937 m per foot); current work is normally metres or international feet (exactly 0.3048 m per foot). The difference is about two parts per million — 3.2 mm per mile — so the choice matters over long lines.
Zones that run mainly east-west use Lambert Conformal Conic with two standard parallels; zones that run mainly north-south use Transverse Mercator with a central meridian and a scale factor of 0.9999 (0.9996 in Alaska). Choose the zone and this converter applies the right projection automatically.
Current zones exist in both NAD83 and NAD27. This converter works in NAD83 on the GRS80 ellipsoid. NAD27 coordinates differ from NAD83 by up to about 100 m in places and must be transformed between datums first.
The projection agrees with the EPSG reference implementation to within 0.017 mm forward and 0.046 mm inverse on test points across all zone types. Your input precision and the datum of the source coordinates are almost always the larger source of error.
Because the false easting does not have to be geographically meaningful — it only has to keep every coordinate in the zone positive and reasonably short. A round 500,000 m easting achieves that for a zone a few hundred kilometres wide, so the same value is reused across many states.
Yes — free, with no login, no account and no usage limit. Every conversion runs locally in your browser, so your coordinates are never uploaded.
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