Free Tool

Great-Circle & Rhumb-Line Calculator

Distance, initial/final course and vertex on the great circle — against the constant-course rhumb line. The classic sailing comparison.

ILLUSTRATIVE TELEMETRY · NOT LIVE DATALAT 51.9244°NLON 4.4777°ESOG 12.4 KNHDG 087°TWS 18 KT NWSWELL 2.1 MSIG −38 DBNO LIVE AIS FEEDECDIS NOT CONNECTEDUTC --:--:--ILLUSTRATIVE TELEMETRY · NOT LIVE DATALAT 51.9244°NLON 4.4777°ESOG 12.4 KNHDG 087°TWS 18 KT NWSWELL 2.1 MSIG −38 DBNO LIVE AIS FEEDECDIS NOT CONNECTEDILLUSTRATIVE TELEMETRY · NOT LIVE DATALAT 51.9244°NLON 4.4777°ESOG 12.4 KNHDG 087°TWS 18 KT NWSWELL 2.1 MSIG −38 DBNO LIVE AIS FEEDECDIS NOT CONNECTEDUTC --:--:--ILLUSTRATIVE TELEMETRY · NOT LIVE DATALAT 51.9244°NLON 4.4777°ESOG 12.4 KNHDG 087°TWS 18 KT NWSWELL 2.1 MSIG −38 DBNO LIVE AIS FEEDECDIS NOT CONNECTED

Departure latitude (°N)Departure longitude (°E)Arrival latitude (°N)Arrival longitude (°E)

Decimal degrees, WGS84-style — e.g. Singapore 1.29, 103.85 · Rotterdam 51.95, 4.14. West/south negative.

Great-circle distance5700.5 nm

Initial course322.43°T

Final course261.53°T

Vertex (highest latitude)52.44°N, 14.84°E

Rhumb-line (Mercator) distance5920.0 nm

Rhumb-line course (constant)296.93°T

GC saving vs rhumb219.4 nm (3.71%)

Spherical sailing mathematics per Bowditch (The American Practical Navigator). Great-circle = shortest path with continuously changing course; rhumb line = constant compass course, longer except on meridians/equator. Planning figures — not a passage plan.

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Method

Spherical navigation, per Bowditch.

Great circle

Shortest path on the sphere — course changes continuously; the vertex marks the highest latitude reached.

Rhumb line

Constant compass course via Mercator sailing — longer than the GC except on meridians and the equator.

Planning only

Exact math on a spherical Earth — WGS84 charts will differ slightly. Not a passage plan.

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