The voyage
The answer
Choose two ports to see the distance.
Only the two ports are sent to Neptune Atlas. Your speed, fuel figures and dates stay in your browser.
How the sea distance is calculated
A ship cannot sail in a straight line between two ports, because land is in the way. The shortest line on a globe is called a great circle. From Singapore to Rotterdam it is about 5,688 nautical miles, and it crosses Asia and Europe. The real voyage by sea is about 8,398 nautical miles.
This calculator finds the shortest path that stays in water a ship can use. It works on a map of the world’s seas built from public depth data, with the Suez, Panama and Kiel canals opened and the Arctic closed. The route keeps clear of the coast, goes through the straits ships really use, and is measured in nautical miles along its whole length. One nautical mile is 1.852 kilometres.
The formulas for days and bunker cost
speed made good speed x (1 - sea margin) days at sea distance / speed made good / 24 voyage time days at sea + canal time arrival (ETA) departure + voyage time bunkers days at sea x fuel used per day bunker cost bunkers x fuel price
The sea margin is taken off the speed, because bad weather slows the ship. Canal time is the transit plus the usual wait: 30 hours for Suez, 28 for Panama and 12 for Kiel.
Worked example: Singapore to Rotterdam at 12.5 knots
distance 8,398 nm by the Suez Canal speed made good 12.5 x (1 - 5%) = 11.875 knots days at sea 8,398 / 11.875 / 24 = 29.47 days voyage time 29.47 + 1.25 (Suez) = 30.72 days bunkers 29.47 x 25 t/day = 736.7 t bunker cost 736.7 t x $600 = about $442,000
Leave at 08:00 on 1 March and the ship arrives early on 1 April. Without the Suez Canal the same voyage goes round the Cape of Good Hope and is about 11,850 nautical miles, which adds about 11 days.
What this calculator does not do
It measures one port pair, not a voyage with several ports. It uses one fuel price, so it does not price the dearer fuel burned inside an emission control area. It does not count fuel burned in port or at anchor, or canal tolls. And it is a planning figure, not a passage plan: the master chooses the real route.
Questions
- Is this sea distance calculator free?
- Yes. There is no account and no sign-up. One visitor can calculate up to 100 routes a day, which is there only to stop automated copying.
- How do I calculate the distance between two ports?
- Type each port name or its UN/LOCODE, for example SGSIN for Singapore, and pick it from the list. The distance in nautical miles appears as soon as both ports are chosen.
- How do I work out the ETA?
- Divide the distance by the speed the ship will really make, then by 24 to get days. Add canal time, then add the result to the departure time. The calculator does this when you enter a speed and a departure.
- What is a sea margin?
- An allowance for weather. A ship rated at 12.5 knots in good weather does not hold it for a whole voyage, so planners take a percentage off the speed. 5% is usual on an ocean passage.
- Why is the distance different from other tables?
- Distance tables differ by a few percent, because each one picks its own point for the port and its own track through straits and around headlands. Use the same source for every voyage you compare.
- Which ports are covered?
- About 1,600 commercial sea ports, each with a UN/LOCODE, the standard United Nations code for a trade location. The full product routes from any position at sea.
Worth reading: emission control areas on why miles inside an ECA cost more, and bunkers and fuel grades on what a ship burns. The distances on busy routes are also listed as port to port sea distances, one page a route. To turn the days into earnings, use the free TCE calculator. There are also a free laytime calculator and an IMO number checker.
Neptune Atlas uses the same sea routes in its voyage estimator, for voyages with several ports and for each ship’s own fuel use. See what it costs.