Latitude and longitude to Maidenhead locator

Model: IARU Maidenhead locator: 18×18 fields, 10×10 squares, 24×24 subsquares, and the extended pairs; a point on a grid line falls in the cell east or north of it, and +90° and +180° in the last cell

Accuracy: Exact (integer cell arithmetic); matches an independent implementation of the definition

When to use this: Use this for amateur radio and anything that follows it: a Maidenhead or QTH locator identifies a station's square in two to ten characters, and contest logs, propagation reports, and antenna-aiming software all speak it. Give a position and it returns the locator at the length you want, with the square's bounds. Six characters is the usual exchange, eight or ten when a station wants to be pinned down for a contest or for microwave work.

Limitations: A locator is a square, not a point: the common six-character form is about five kilometers by two and a half, and the square's ground size changes with latitude because it is defined on degrees. Distances computed between two locators are between square centers and inherit that uncertainty. Beyond eight characters the extra precision is finer than most stations know their own position to, so it implies more than it delivers.

Worked example: Pittsburgh at 6 characters. Source: add-geodesy-suite scenario: FN00ak. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

Review: Not yet independently reviewed by a geodesist.

Last verified: 2026-09-19, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.1.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-19, changed: The GARS, GEOREF, Maidenhead, and USNG tools are stable, both directions. They reproduce NGA's GARS band definitions, the Wikipedia GEOREF (NAS Patuxent River) and Maidenhead (W1AW) examples, and the FGDC USNG Washington Monument, and match GeographicLib, pygeodesy, an exact Maidenhead reference, and NGA GEOTRANS on thousands of points. Results are unchanged apart from the fix below. Changelog
• 2026-09-19, fixed: A longitude or latitude typed on a Maidenhead grid line in decimal degrees (like 145.83333333333334 for 145°50′) could land in the cell on either side of the line, depending on floating-point rounding. It now always falls in the cell east or north of the line. The tool is now version 1.1.0. Changelog

Checked against: 23 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• VHF Managers Handbook: the Maidenhead Locator System, International Amateur Radio Union, Region 1, IARU Region 1 VHF Managers Handbook, version 10.03. The QTH locator: fields, squares, subsquares, and extended squares.