Calculate the sea distance between two ports
Ships can't sail in a straight line. A sea route has to go around continents, through canals and along the shipping lanes, so the distance at sea is almost always longer than the great-circle distance you'd measure on a globe — often by 20% or more, and sometimes double. This calculator routes between any two ports or coastal cities over a global shipping-lane network and shows both numbers side by side, with the detour as a percentage.
Canals change everything. Shanghai to Rotterdam through the Suez Canal is roughly 10,600 nautical miles; around the Cape of Good Hope it's several thousand more. New York to Los Angeles is about 5,000 nautical miles through the Panama Canal, less than half the distance of sailing around South America. The route summary lists every canal and strait the voyage passes through, from Malacca and Hormuz to Gibraltar and the English Channel.
Voyage time follows from distance and speed. Pick a preset — container ship at 16 knots, bulk carrier at 13, sailing yacht at 6 — or type your own speed, and the calculator converts the sea distance into days and hours at sea. Switch units between nautical miles, kilometers and miles, then download the map as a PNG for a report, a quote or a lesson.
Frequently asked questions
How accurate is the sea route distance?
It's a planning estimate. The route follows real shipping lanes rather than a straight line, so on the major trade lanes it lands close to published port-to-port distance tables — Shanghai to Rotterdam via Suez comes out around 10,600 nautical miles. Actual voyages vary with traffic separation schemes, weather routing and pilot stations, so don't use it for navigation.
Where does the route data come from?
Routes are calculated over an open global network of shipping lanes — the marine network used by the open-source searoute project — with the shortest path found between the lanes nearest your two points. Where the lanes don't reach, such as small harbors and islands, the route finishes over open water around the coast.
What is a nautical mile?
A nautical mile is exactly 1,852 meters (about 1.15 statute miles). It is based on one minute of latitude, which is why shipping and aviation use it. Speeds at sea are given in knots: one knot is one nautical mile per hour.
How is the voyage time estimated?
Voyage time is the sea distance divided by the speed you enter, in knots, assuming the ship holds that speed the whole way. Typical speeds are about 16 knots for a container ship, 13 for a bulk carrier and 6 for a sailing yacht. Port calls, canal queues, bunkering and weather are not included.
Which canals and straits does it detect?
The calculator flags the Suez Canal, Panama Canal, Strait of Gibraltar, Strait of Malacca, Cape of Good Hope, Bab-el-Mandeb, Strait of Hormuz, English Channel and Bosporus when the route passes through them, so you can see at a glance which chokepoints a voyage depends on.
Is the sea route calculator free?
Yes. It's free with no account required, and you can download the route map as a PNG with the distance and voyage time on it. To turn the voyage into an animated video, open it in Mapimator Studio.