Sailing Route Distance Planner - Leg Distances and Sailing Time

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What it is

A sailing route distance planner turns a list of waypoints into leg distances, total distance, and an estimated sailing time. Waypoints are simply latitude and longitude pairs for each stop or turning point, and the tool measures the distance between each pair in turn, so you can see which leg is the long one and where a day’s sailing ends.

It reports two kinds of distance. Great-circle distance is the shortest path over the Earth’s surface, the route a plane would fly. Rhumb-line distance follows one constant compass course, which is how many sailors actually steer on short legs. On coastal hops the two are almost identical, but on ocean legs the difference grows.

How to use it

Type one waypoint per line as latitude, longitude, using decimal degrees with a minus sign for south latitudes and west longitudes. London is about 51.5, -0.12. Add your planned speed in knots, then press Calculate. The table shows each leg in kilometres for both distance types, plus totals in kilometres and nautical miles and an estimated time.

Order matters: waypoints are joined in the order you type them, so list them in sailing order, and include any waypoint where you must turn around land or a hazard rather than drawing a straight line through it.

Worked example

Three waypoints from London to Paris to Marseille give a total great-circle distance of about 1,050 kilometres, or roughly 570 nautical miles. At a planned speed of 6 knots, straight-line sailing time is about 95 hours, or four days of non-stop sailing. Real sailing takes longer, because you stop, slow for weather, and route around coasts.

The leg table shows the second leg is much longer than the first, which is the kind of fact that changes where you plan overnight stops. A route that looks short on a map often hides one very long day.

How to read your result

Great-circle total is the shortest possible distance and the one to use for a rough time estimate. Rhumb-line total is slightly longer and closer to what a constant-course passage actually sails. Nautical miles are the unit sailors use at sea: one nautical mile is 1.852 kilometres, and speed in knots is nautical miles per hour, so the time estimate divides nautical miles by knots.

If the two totals differ by more than a few percent, you are looking at a long leg where the choice of route shape genuinely matters.

Common mistakes

The biggest mistake is joining two distant waypoints with a straight line that crosses land, a reef, or a restricted area. The tool measures geometry, not safe water, so break the route into safe waypoints yourself. Another mistake is entering longitude with the wrong sign, which can put a waypoint on the wrong side of the world.

Limits

Distances are computed on a spherical Earth, which is accurate to well under one percent for planning, but this is not a navigation tool. It does not know about depths, traffic, weather, currents, or hazards. Always plan on official charts, check forecasts, and keep a proper passage plan before you sail.

Questions people ask

What is a nautical mile?

One minute of latitude, equal to 1,852 metres. Because knots are nautical miles per hour, distance in nautical miles divided by speed in knots gives hours directly.

Should I sail the great-circle or the rhumb-line route?

On short coastal legs, steer the rhumb line: it is simpler and barely longer. On long ocean legs, a great-circle route saves real distance, sailed as a series of short rhumb-line legs.

Why does the time estimate look too short?

It is straight-line time at your planned speed with no stops, no weather delays, and no current. Add a generous margin, and plan daily distances you can actually sustain.

Sailing Route Distance Planner – Leg Distances and Sailing Time