Nautical Unit Converter
Convert between knots, km/h, mph, nautical miles, fathoms, and all the other units sailors and mariners need. Type a value and see all unit equivalents instantly. Includes Beaufort scale lookup and passage time calculator. Nothing uploaded.
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Learn more: Nautical measurement and maritime distance
Why nautical miles differ from statute miles
Nautical miles are based on Earth's circumference and the degrees of latitude - one nautical mile equals one arc-minute of latitude, or roughly 1.852 kilometers. Statute miles (the US/UK standard) are terrestrial measurements with no geographic basis. Nautical miles are used globally for marine and aviation navigation because latitude and nautical miles have a direct relationship: traveling north or south 60 nautical miles changes your latitude by exactly one degree. This makes course plotting straightforward. A knot is a nautical mile per hour, still the standard for ships and aircraft. Converting between nautical and statute miles is essential when planning ocean voyages, reading nautical charts, or working with aviation charts.
Fathoms, cables, and historical maritime units
Fathoms (6 feet) were traditional depth measurements - a sailor would drop a weighted line called a lead line and count the fathoms to the bottom. Cables are nautical units equal to 1/10 of a nautical mile, still used in some navigation contexts. These older units persist in maritime tradition and older charts, though modern depth is typically given in meters. This calculator includes these historical units for reference and for those working with legacy maritime documents or traditional navigation techniques.
FAQ
Why do ships use knots instead of kilometers per hour?
Knots (nautical miles per hour) directly correspond to latitude-based navigation. If you travel 1 knot due north, you move exactly 1 arc-minute of latitude in one hour, simplifying course calculations on nautical charts. This convention is maintained globally for marine and aviation use.
Is a nautical mile larger than a statute mile?
Yes. One nautical mile equals about 1.852 kilometers or 1.151 statute miles. A 100-nautical-mile voyage is roughly 115 statute miles. This difference matters for voyage planning and fuel calculations.
When would I use fathoms or cables?
Fathoms appear on older nautical charts and in traditional maritime documentation. Cables are sometimes used in naval contexts or when describing short distances at sea. Modern navigation typically uses meters for depth and nautical miles for distance, but these historical units remain part of maritime knowledge.