QSL Card Distance Calculator

Maidenhead grid locators encode a station's approximate location as a short alphanumeric code — the field (a 20°-longitude by 10°-latitude cell, A through R), the square (a 2°×1° subdivision, 0-9), and the subsquare (a 5'×2.5' refinement, a through x) — and this calculator decodes two such locators back into latitude/longitude before running the standard haversine great-circle formula, d = R × 2·atan2(√a, √(1-a)), to get the distance between them. It also computes the initial great-circle bearing (the compass heading to point a directional beam antenna) using the standard atan2-based bearing formula. Because radio waves can travel either the short way around the globe or the long way, it reports both: the short-path distance and bearing, plus the long-path distance (Earth's circumference minus the short path) and the reciprocal bearing 180° opposite — useful because HF propagation sometimes favors the long path over the short one depending on which route currently has daylight or favorable ionospheric conditions.

An estimated HF hop count divides the distance by roughly 3,500 km, a commonly-used rough ceiling for a single ionospheric skip, to suggest how many bounces off the ionosphere a signal would need to cover the path. Since a 4-character grid locator only pins down location to within roughly 100km × 150km at mid-latitudes (the square resolution — coarser than the subsquare defined above), treat the resulting distance and bearing as good-enough for pointing a beam or logging a contact, not survey-grade precision — a 6-character grid would narrow that considerably.