A sailing distance calculator answers two questions: how many nautical miles between here and there by water, and how long that takes at your speed. The catch is that boats do not sail straight lines, so a good calculator routes around land, through the right straits, and along real sea lanes. Here is how the calculators work, verified distances for routes you can check us on, and the time math at typical sailing speeds.
- Sea distance runs along practical routes, not straight lines: often 5 to 30 percent longer than the great circle.
- Good calculators route over a shipping-lane network and let you pick canal and strait options.
- Time = distance / speed: 192 nm at 5.5 knots is about 35 hours; at 20 knots, under 10.
- Verify any calculator against known routes before trusting it on unknown ones.
- For 56 pre-computed routes, published tables answer the question with zero setup.
#Why the straight line is wrong
The great-circle distance between two harbors is geometry; the sailing distance is geography. Coastlines, islands, shoals, and traffic separation schemes bend every real route, and the detour is rarely small: our engine measures New York to Los Angeles at 4,943 nautical miles via Panama against a straight line that cheerfully cuts through two continents. Any calculator that returns great-circle numbers for port pairs is answering a different question than the one a sailor asked.
#Verified distances you can check us on
- Miami to Nassau: 192 nm. At 5.5 knots about 35 hours; a classic overnight passage.
- Sydney to Hobart: 554 nm port to port; the famous race course measures 628 nm along its marks.
- New York to Los Angeles: 4,943 nm via the Panama Canal.
- Rotterdam to Singapore: 8,439 nm via Suez; avoiding Suez adds roughly 3,400 nm around the Cape.
These come from the same engine behind our sea distance pages, which publish 56 port-to-port routes with voyage times at typical speeds. Spot-check them against any source you trust; reproducing known routes is the only honest test of a distance calculator.
#From distance to time
Divide nautical miles by knots and you have hours. The number that matters is your realistic average, not your best day: cruising sailboats plan on 5 to 6.5 knots, and what that means per day is covered in how far a boat travels in a day. For motor yachts the same distance is a fuel question as much as a time question, which is the fuel calculator guide's territory.
#Calculating a custom route
For pairs not in any table, use a routing calculator: the Marine OS route planner takes two ports or any two points, suggests the sea route over the global shipping-lane network with canal and strait choices, and returns the distance, time at your speed, and editable waypoints so the estimate becomes an actual plan. Developers can pull the same numbers from the Route API.
Once the calculator says 192 nm, the real questions begin: which weather window, what fuel and reserve, which waypoints keep you off the banks, and who ashore holds the float plan. A calculator that hands its result to a route planner saves you re-entering everything.
Marine OS is marina management software, and the Marine OS route planner doubles as a sailing distance calculator: two points in, sea distance and time out, then waypoints, weather, and a float plan on the same screen.
Calculate your route's real sea distance
Distance over the shipping-lane network, time at your speed, and a route you can refine, in the browser.
#Frequently asked questions
Frequently asked questions
Check the table first, calculate the custom pairs, and turn the number into a plan. Start at the sea distance pages or go straight to how to plan a boat route.
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