Maidenhead Grid Locator Converter

Convert between latitude / longitude and a Maidenhead grid locator — the concise grid-square system used worldwide by amateur radio operators to report position (e.g. IO91wm for London, FN31mp for Connecticut). Encode a position to a 4, 6 or 8-character locator, or decode a locator back to its centre and bounding box. The grid nests field (20°×10°, two letters), square (2°×1°, two digits) and subsquare (5′×2.5′, two letters), with an optional 8-character extension. Pure arithmetic, in your browser.