Decimal degrees ↔ DMS ↔ UTM ↔ California State Plane (NAD83, zones 1–6, US survey feet). Full Lambert conformal conic and transverse Mercator math, computed locally — nothing leaves this page. Inputs persist in this browser via localStorage.
Datum & accuracy notes, read once: This tool works in NAD83/GRS80. GPS/phone/OSM coordinates are WGS84, which differs from NAD83 in California by roughly 1–2 m — irrelevant for finding a manhole, unacceptable for boundary or control work. NAD27 is a different datum entirely (~90 m off here) and cannot be converted with closed-form math — that needs NADCON/HTDP in real software. Before trusting this tool on anything that matters, verify it against a known NGS control point in your zone (pull a datasheet, punch in the published lat/lon, confirm the published SPCS coordinates come back).
All Formats
Decimal degrees
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DMS
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UTM (NAD83, m)
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CA SPCS (NAD83, US ft)
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How the Numbers Are Derived
Projections implemented
Both directions of two map projections on the GRS80 ellipsoid (a = 6,378,137 m, 1/f = 298.257222101), straight out of Snyder's Map Projections — A Working Manual [USGS PP 1395]:
Lambert Conformal Conic (2 standard parallels) for California State Plane. Each zone is defined by two standard parallels, a latitude/longitude of origin, and false easting/northing of 2,000,000 m / 500,000 m. Native units are meters; the display converts to US survey feet (1 ft = 1200/3937 m exactly — the survey foot, not the international foot, which differs by ~2 ppm and matters at State Plane magnitudes).
Transverse Mercator for UTM (k₀ = 0.9996, 6° zones, 500,000 m false easting). California spans zones 10 and 11, split at 120°W.
The series formulas are accurate to well under a millimeter within a zone — the practical error budget is entirely datum handling and input quality, not the math.
What happened to Zone 7
Under NAD27, California had seven State Plane zones; Zone 7 was Los Angeles County alone. When the system was redefined on NAD83, Zone 7 was merged into Zone 5, leaving six zones. Old LA-area drawings labeled "Zone 7" are NAD27 coordinates — different datum, different zone constants, roughly 90 m from their NAD83 equivalents. Converting them properly requires NADCON grid-shift files (QGIS, proj, or NGS's online tools do this correctly); no closed-form approximation is safe for anything you'd stake or stake a claim on.
Practical notes
West longitude is negative in decimal degrees. A California point with a positive longitude is in China; the tool warns.
SPCS grid distance ≠ ground distance. The grid scale factor within a zone is designed to stay within about 1:10,000, but on long lines and precise work the combined factor matters — that's survey territory.
For OSM work, treat WGS84 and NAD83 as identical (the ~1–2 m difference is below aerial-imagery alignment error anyway). For control, don't.
NAD83 has realizations (HARN, CORS96, 2011...) that differ at the centimeter-to-decimeter level. This tool doesn't distinguish them; survey-grade work uses NGS tools that do.
References
Snyder, J.P., Map Projections — A Working Manual, USGS Professional Paper 1395. https://pubs.usgs.gov/pp/1395/report.pdf
NGS — State Plane Coordinate System zone definitions and datasheets (for verification control points). https://geodesy.noaa.gov/
EPSG registry — CA SPCS NAD83 zones are EPSG 2225–2230 (meters). https://epsg.org/