Sea Distance Calculator
Pick two ports and get the distance a ship actually sails, the canals it passes and how long the passage takes at your speed. Free, with no sign-up.
- 3,099 ports
- Canals and straits
- Free, no sign-up, no limit
Calculate a sea route
Rotterdam to Singapore by sea
8,423nautical miles
15,599 km · 9,693 milesVia Strait of Dover, Strait of Gibraltar, Suez Canal, Bab-el-Mandeb, Strait of Malacca
- Time at sea at 14 knots
- 25 days 2 hours
- Straight line
- 5,704 nm The sea route is 48% longer
How to Calculate a Sea Distance
Three steps from two port names to a passage time
Pick the two ports
Type a port name in each field and choose it from the list. The list covers about 3,100 commercial ports in 175 countries.
Set the speed
Enter the speed in knots. A container ship cruises at 14 to 20 knots, a bulk carrier at 11 to 14 and a cruise ship at around 18.
Read the route
You get the sea distance in nautical miles, kilometers and miles, the canals and straits on the way, and the days and hours at sea.
A Sea Route, Not a Straight Line
What the calculator takes into account
Real shipping lanes
Routes follow a global maritime network built from shipping lanes, so a voyage goes around continents and through canals instead of across land.
Canals and straits
The result names every canal and strait on the route, such as the Suez Canal, the Panama Canal or the Strait of Malacca.
Passage time
Distance divided by speed gives the days and hours at sea, the starting point for an ETA. Time in port and in canal queues is not included.
Free, with no limit
No account and no daily cap. The calculation runs on our server and costs you nothing.
Who Uses a Port Distance Calculator
Shippers and freight forwarders
Estimate the transit time of a container or bulk shipment and check whether a quoted schedule is realistic.
Seafarers and students
Plan a passage, check a voyage calculation or practise distance, speed and time problems for a navigation exam.
Families of crew and cruise passengers
See how far a ship has to go between two ports and roughly when it gets there.
Frequently Asked Questions
Everything you need to know about the Sea Distance Calculator.
How is the sea distance calculated?
The calculator finds the shortest route between the two ports on a global maritime network of shipping lanes, canals and straits, then measures its length along the curve of the Earth. Arctic passages are left out because they are closed by ice for most of the year.
How accurate is the distance?
On voyages over 1,000 nautical miles the result is usually within about 4 percent of published port distance tables. Short coastal trips are less exact, because the real track depends on pilot stations, fairways and harbour approaches; there the calculator never shows less than the straight line distance.
What is a nautical mile?
A nautical mile is exactly 1,852 meters, about 1.15 statute miles. It equals one minute of latitude, which is why ships and aircraft measure distance in nautical miles and speed in knots, one nautical mile per hour.
How do I work out the ETA of a ship?
Divide the distance in nautical miles by the speed in knots to get hours at sea, then add the departure time. A real ETA also depends on weather, canal waiting times and port congestion, so the passage time here is the minimum, not a promise.
Why is the route longer than the straight line?
A ship cannot cross land. Rotterdam to Singapore is about 5,700 nautical miles in a straight line but about 8,400 by sea, through the Strait of Gibraltar, the Suez Canal and the Strait of Malacca.
Can I see where a ship on this route is right now?
Yes, in the Primo Nautic app. It shows a ship's live position, where it is heading and its predicted arrival, and with Primo Nautic Premium it sends an alert when it reaches port.
Know When It Arrives
Loved the Sea Distance Calculator? Primo Nautic tracks any vessel live and shows when it will arrive. Free on iOS and Android.
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