Maritime Calculators & Tools
Free, practical calculators for life and work at sea — speed conversion, nautical distance and ETA, cargo TEU counting, ship tonnage and displacement, watch scheduling, and sea-service time. Educational tools for planning and learning, not a substitute for official passage planning, stability calculations, or certification guidance.
Knots Speed Converter
Convert a vessel's speed between knots, miles per hour, kilometres per hour, and metres per second — the everyday conversion for reading a speed log, a weather forecast, or a passage plan
Nautical Distance & ETA Calculator
Work out passage time from distance and speed, or the great-circle distance in nautical miles between two latitude/longitude positions, then read the ETA at your planned speed of advance
Cargo TEU Calculator
Turn a mix of 20-foot, 40-foot, and 45-foot boxes into a total TEU count and physical container total — the twenty-foot-equivalent-unit maths behind container-ship capacity and terminal throughput
Ship Tonnage Calculator
Estimate gross tonnage from enclosed volume with the Moorsom K1 formula, and displacement and deadweight from length, beam, draft, and block coefficient — the tonnage basics behind a ship's size and cargo capacity
Watch Schedule Planner
Turn your crew size and a watch system — four-on-eight-off, six-on-six-off, or four-on-four-off with dog watches — into a clear rotation showing who has the watch and each hand's hours on duty per day
Sea Time Calculator
Add up sign-on and sign-off dates across voyages into total sea-service days and months — the qualifying-sea-time tally seafarers keep for STCW certificates of competency and licence renewals