Sailing Distance Calculator

Calculate nautical distances, bearings, and estimated arrival times for your voyage

Starting Point Coordinates

Destination Coordinates

Average Speed (knots)

Distance

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Initial Bearing

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Estimated Time of Arrival

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How to Calculate Sailing Distance

Calculating the distance between two points at sea requires accounting for the curvature of the Earth. This calculator uses the Haversine formula, which determines the shortest distance between two points on a sphere. The result is expressed in nautical miles, the standard unit of measurement for maritime navigation.

Step-by-Step Guide

Obtain the latitude and longitude coordinates of your starting point. These can be found on nautical charts, GPS devices, or mapping applications.
Enter the coordinates of your destination in the same format. Latitude values range from -90 to 90 degrees, whilst longitude ranges from -180 to 180 degrees.
Input your vessel’s average cruising speed in knots. Consider factors such as sea conditions, wind, and currents when estimating this value.
Click the calculate button to receive your distance in nautical miles, the initial compass bearing, and your estimated sailing time.

Example Route: From Portsmouth (50.7645°N, 1.2977°W) to Guernsey (49.6500°N, 2.5333°W) at 6 knots would cover approximately 82 nautical miles, taking roughly 13 hours and 40 minutes on a bearing of approximately 139 degrees.

About Nautical Miles and Sailing Calculations

What is a Nautical Mile?

A nautical mile is defined as one minute of latitude, equivalent to 1.852 kilometres or approximately 1.15078 statute miles. This unit was specifically developed for maritime and aviation navigation because it directly relates to the Earth’s geometry. When you sail one minute of latitude north or south, you have travelled one nautical mile.

The Haversine Formula

This calculator employs the Haversine formula, a mathematical equation used since the 1800s to calculate great-circle distances. The formula accounts for the Earth’s spherical shape, providing far more accuracy than simple Pythagoras theorem-based calculations. It determines the shortest path across the surface of a sphere between two points, which represents the most efficient sailing route in open water.

Great Circle Routes

The calculated distance represents a great circle route, which is the shortest path between two points on the globe. Whilst this provides an excellent baseline for planning, actual sailing routes may differ due to weather patterns, shipping lanes, navigational hazards, or coastal geography. Always consult current nautical charts and weather forecasts before finalising your route.

Voyage Planning Considerations

Factors Affecting Sailing Time

The estimated time of arrival provided by this calculator assumes constant speed and direct routing. In reality, several factors can influence your actual sailing time:

Wind conditions: Headwinds can significantly reduce speed, whilst favourable winds may increase it.
Sea state: Rough seas typically slow progress and may require course alterations.
Tidal currents: These can either assist or hinder your passage, particularly in coastal waters.
Navigation around obstacles: Islands, shallows, and restricted areas may require deviations from the direct route.
Crew rest requirements: On longer passages, you may need to reduce sail or heave-to for rest periods.

Planning Daily Distances

For leisurely cruising, many sailors plan for 20-25 nautical miles per day, allowing 4-5 hours of active sailing. This leaves adequate time for anchoring, exploring ports, and enjoying stops along the way. More experienced crews on passage might cover 100-150 nautical miles per day in favourable conditions, whilst offshore racing can see daily runs exceeding 200 nautical miles.

Frequently Asked Questions

How accurate is this sailing distance calculator?

This calculator provides highly accurate great-circle distances based on the Haversine formula. The mathematical precision is suitable for passage planning, though actual sailed distance may vary due to tacking, avoiding hazards, following shipping lanes, or accounting for weather conditions. For coastal navigation or routes with multiple waypoints, consider breaking your passage into segments and calculating each separately.

What speed should I enter for my yacht?

Enter your vessel’s typical cruising speed under average conditions. For most cruising yachts, this ranges from 5 to 7 knots. Racing yachts may average 8-10 knots or more, whilst motor yachts can sustain 15-25 knots. Consider your boat’s hull speed, typical sail configuration, and expected conditions. When in doubt, use a conservative estimate to avoid overestimating your daily progress.

How do I find coordinates for ports and anchorages?

Coordinates can be obtained from nautical charts, pilot books, cruising guides, or digital navigation applications. Most GPS chartplotters allow you to select a location and display its coordinates. Online resources such as maritime port databases also provide accurate position data. Always verify coordinates against official nautical charts before relying on them for navigation.

Can I use this calculator for multiple waypoints?

This calculator determines the direct distance between two points. For routes with multiple waypoints, calculate each leg separately and sum the distances. For example, if sailing from Point A to Point C via Point B, first calculate A to B, then B to C, and add the results together for your total passage distance.

What is the difference between true bearing and magnetic bearing?

The bearing provided by this calculator is a true bearing, referenced to true north (the geographic North Pole). To convert this to a magnetic bearing for compass navigation, you must apply the magnetic variation (declination) for your location. This variation changes depending on where you are in the world and gradually shifts over time. Current magnetic variation can be found on nautical charts or from your GPS system.

How should I account for tidal currents?

Tidal currents can significantly affect your course and speed over ground. This calculator provides speed through the water calculations. To account for currents, consult tidal stream atlases or your electronic chartplotter’s current predictions. A 2-knot favourable current can reduce a 12-hour passage to 10 hours, whilst an opposing current of the same strength would extend it to 15 hours. Plot your passage accounting for current direction and strength at different times.

Practical Sailing Tips

Preparing for Coastal Passages

When planning coastal passages around the UK, Channel Islands, or European waters, always check weather forecasts from the Met Office or your local meteorological service. Study tidal information carefully, as UK waters experience some of the world’s most significant tidal ranges. The Solent, for instance, has complex tidal patterns that require careful planning.

Offshore Passage Making

For longer offshore passages, prepare a detailed passage plan that includes waypoints, estimated positions at regular intervals, emergency ports of refuge, and communications schedules. Calculate fuel requirements with a safety margin, provision adequately, and brief your crew on watch systems and emergency procedures. Monitor weather patterns several days before departure and be prepared to delay if conditions deteriorate.

Safety Margins

Always build safety margins into your calculations. Arrive at destinations with adequate daylight for safe entry, account for unexpected delays, and carry sufficient fuel and provisions for extended passages. Many experienced sailors add 20-30% to calculated passage times to account for unforeseen circumstances such as light winds, equipment issues, or route alterations.