Ship Speed Knots MPH Converter
Converts ship speed in knots to km h, miles per hour and meters per second showing equivalents in common nautical and metric units.
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Ship speed: knots, km/h and mph
At sea and in the air, speed is measured in knots (kt), where 1 kt = 1 nautical mile per hour = 1.852 km/h = 1.151 mph. The name goes back to the old "chip log", a line knotted at fixed intervals that sailors paid out over the stern for 28 seconds. The math is straightforward: km/h = kt × 1.852 and mph = kt × 1.151. So a cargo ship at 18 kt is doing 33.3 km/h, or 20.7 mph. For context, container ships and bulk carriers cruise around 12–25 kt, nuclear submarines push past 30 kt submerged, a frigate or "naval Concorde" clears 30 kt, and the SS United States took the Blue Riband at 35.6 kt back in 1952.
Applications
ECDIS electronic chart navigation. COLREG collision-avoidance rules, which spell out speed-related give-way obligations. AIS broadcasts, which report in kt. ANTAQ port-arrival reports in Brazil. Fuel-consumption planning, where drag scales somewhere between v² and v³, so easing off from 22 to 18 kt can shave burn by 30% or more. And ETA calculations for cargo and cruise lines.
FAQ
Why not just use km/h at sea? One nautical mile is one minute of arc along a meridian, so 1 kt on a chart maps directly onto angular position. For celestial and GPS navigation, that turns out to be far handier than working in metric units.
Is "knots per hour" correct? No. A knot already means nautical miles per hour, so "knots per hour" would describe an acceleration. It's a common slip.
Are aviation knots the same? They are. 1 kt = 1.852 km/h whether you're on a ship or in a cockpit, and that shared unit is exactly why ATC and ship bridges speak the same language.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.