State Plane, UTM & Lat/Long Coordinate Converter

What this tool does

Converts a single point between latitude/longitude, State Plane and UTM, on either NAD83 or NAD27. Enter coordinates in one system and read them back in the others, each output with its own datum, zone and units, so a NAD83-in, NAD27-out conversion works directly.

Every calculation runs in your browser through proj4; nothing is sent anywhere. If you do not know your State Plane zone, pick the state and county and the tool fills it in.

Formula

Projections are handled by proj4. The one conversion worth doing in your head is between the three ways of writing an angle.

Assumptions

Built for quick field conversions, not survey-grade control work.

• Horizontal Only, No elevations, vertical datums, or geoid corrections.
• Identify the system first, Northing/Easting values alone do not identify the coordinate system. The same kind of numbers may be State Plane, UTM, a local or project grid, or something else. Identify the system from the drawings before converting.
• NAD27 Accuracy, NAD27-to-NAD83 results depend on the transformation method, geographic area, and source data. Approximate transformations are not suitable for survey control. Use an appropriate NGS transformation when higher accuracy is required.
• NAD83 Realizations, NAD83 has multiple realizations, such as NAD83(2011). Where the source documents identify a realization, use that one.
• GPS Coordinates, WGS84 (GPS) and NAD83 are different reference frames. Treating them as interchangeable is only appropriate for approximate location work, not for control.
• Feet Definitions, US Survey Foot = 1200/3937 m exact. International Foot = 0.3048 m exact. The 2 ppm difference is real money at State Plane magnitudes: about 4 ft at a 2,000,000 ft coordinate. The project plans and survey documentation determine which definition applies.
• Zone Warnings, The tool warns when a point sits far from the selected State Plane zone's central meridian or outside the chosen UTM zone. Results still compute, but distortion grows. Use the zone that actually contains the point.
• Verify Control, This converter is for checking, locating and translating coordinates. It is not for establishing project survey control; controlling coordinates come from the surveyor of record.

Geographic (Latitude / Longitude)

Angular position on the earth's ellipsoid. Latitude runs north-south from the equator; longitude runs east-west from the Greenwich meridian. Three formats are accepted on input and toggleable on output: decimal degrees (DD), degrees-minutes (DM), and degrees-minutes-seconds (DMS). They're the same angle written three ways, related by 1° = 60 minutes and 1 minute = 60 seconds (see the Formula block).

• Signs and Hemispheres, Conversions run on the absolute value; the sign or hemisphere letter is applied at the end. −79.991135° and 79° 59' 28.09" W are the same longitude. US longitudes are west, so they're negative in decimal form. Enter either a minus sign or N/S/E/W; don't use both.
• Precision, Displayed precision should match the intended field accuracy and the quality of the source data. Extra decimal places do not add positional accuracy. For context, 1 second of latitude is about 101 ft on the ground.

State Plane (SPC)

Each state is divided into one or more zones, each with its own map projection sized to keep distortion small (about 1 part in 10,000). Coordinates are Northing and Easting, most often in US survey feet. State Plane is common on US surveying and construction projects, but local grids and project-specific coordinate systems are also common.

• Zones, Match the datum and zone to the project documentation. Zone definitions differ between datums; the tool only offers zones that exist in the selected datum. Select by zone directly or by state and county.
• Auditable, The output shows the zone name and its EPSG/FIPS code so results can be checked against other software.

UTM

A worldwide grid of 60 north-south zones, each 6° of longitude wide, with coordinates in meters. Used in mapping, GIS and some federal work, among other systems. The lower 48 spans zones 10 through 19.

• Zone Selection, The correct zone follows from longitude. Use Auto on output to let the tool pick it, or enter a zone manually.
• Coverage (US and North America), This is a North American converter, not a world one. State Plane zones are US-only by definition and NAD83/NAD27 are North American datums; UTM is the only system here that is global, and it is handled for the northern hemisphere. That covers 0°–84°N: every US state, Puerto Rico, the USVI, Guam and the CNMI, plus Canada, Mexico, Central America and the Caribbean. A point below the equator is refused with a message rather than converted; American Samoa, at about 14°S, is the one US territory outside the range.
• Units, UTM is defined in meters. A survey-feet display is offered for convenience, but published UTM values are metric.

Datums: NAD83 vs NAD27

A datum is the reference frame coordinates are measured against. The same physical point has different numbers in different datums.

• NAD83, The current US standard. Use it unless your documents say otherwise, and use the realization the documents name where they name one.
• NAD27, The 1927 legacy datum, still found on older plans, deeds, and USGS quads. NAD27 and NAD83 coordinates can differ substantially depending on location. Datum transformations are not simple universal offsets.
• Match the Source, Set the input datum to whatever the drawing or survey states. Converting between datums here is approximate for NAD27 (see Assumptions).

Worked example

Field notes

• Datum first, zone second. A NAD27 number read as NAD83 lands you tens of meters off, varying by location, and nothing about the coordinate itself will tell you.
• State Plane and UTM are different systems, and a coordinate in one is not a coordinate in the other. Mixing them silently is a common source of a shifted site plan.