About this calculator
When you prepare a quote or a schedule, the first question is usually "how far, and how many days?". This calculator gives a quick estimate of the sea distance between two ports and the voyage time, without a paid distance table.
It works in two steps. First it computes the great-circle distance, the shortest path over the Earth's surface between two coordinates, with the haversine formula and an Earth radius of 3,440 nautical miles. Ships cannot sail straight across land; they follow channels, straits and shipping lanes. So the great-circle distance is multiplied by a route factor: about 1.1 for open-ocean routes, 1.2 for regional Asian routes through straits, and 1.3 to 1.5 for routes that detour via the Suez or Panama canals or the Cape of Good Hope. Second, the sea distance is divided by the vessel speed in knots, with a weather margin and the number of port days added for the total transit time.
Pick the ports from the UN/LOCODE search, from the list of major ports, or enter coordinates by hand. The result shows the great-circle distance, the estimated sea distance in nautical miles and kilometres, sailing hours and days, and a simple map sketch. These figures are planning estimates, not official routing distances: real transit times depend on the vessel schedule, port rotation, transshipment and terminal queues. Use carrier schedules for commitments to customers.
Worked example
Tanjung Priok (6.10° S, 106.88° E) → Singapore (1.26° N, 103.84° E):
- Great circle: 7.36° of latitude and 3.04° of longitude apart → about 478 nautical miles
- One degree of arc = 3,440.065 × π ÷ 180 = 60.04 nautical miles
A simple check: two points 1° apart on the equator = 60.04 nm × route factor 1.2 = 72.05 nm (133.4 km). At 12 knots with a 10% weather margin: 72.05 ÷ 12 × 1.1 = 6.6 hours, plus 1 port day.
How to use it
Pick origin and destination
Search by name or UN/LOCODE, choose from the major ports, or type latitude and longitude by hand.
Set the route factor
Use 1.1 for open ocean, 1.2 for regional routes through straits and 1.3–1.5 for canal or round-continent routes.
Enter speed and port days
Enter the service speed in knots, a weather margin and the port days, then read the distance and transit time.