How the sea distance is calculated
The great-circle formula returns the shortest distance across the surface of the earth between two coordinates, using an earth radius of 3,440.065 nautical miles. A routing margin (default 10%) is then applied so the estimate better reflects a realistic sea route around land and through canals.
Use the distance in your voyage workflow
- Feed the routed nautical miles into the Maritime ETA & Required Speed Calculator to get an arrival time.
- Send the same distance to the Marine Fuel (Bunker) & CO₂ Estimator for consumption and emissions.
- Compare speed scenarios in the Distance-Speed-Time Matrix Calculator.
Frequently asked questions
How is sea distance between ports calculated?
This calculator uses the great-circle (haversine) formula on each port's latitude and longitude to produce a straight-line distance in nautical miles, then applies your routing margin to allow for canals, land, and traffic separation schemes.
Why add a routing margin?
Real voyages rarely follow a pure great-circle path — vessels detour around continents, use the Suez or Panama canals, and follow IMO-defined TSS lanes. A 10–20% margin gives a more realistic port-to-port distance estimate.
What is a nautical mile?
One nautical mile equals 1,852 metres (about 1.15 statute miles). Voyage distances and vessel speeds (knots) are always expressed in nautical miles.
Can I feed the distance into an ETA calculation?
Yes. Take the routed distance and vessel speed from this tool and use the Maritime ETA & Required Speed Calculator to get an arrival time, or the Marine Fuel (Bunker) Estimator for fuel and CO₂.
Is the distance suitable for chartering or fixture negotiations?
Use it as an early-stage estimate. For fixture-grade distances always cross-check with a dedicated routing service (e.g. AXSMarine, BLM Shipping, or Veson Distances).