Navigation Distance/Time Calculator 🧭
Calculate travel time and ETA for your boat trip. Enter speed in knots and distance in nautical miles to get arrival time.
How to Use the Navigation Calculator
Enter speed (knots) and distance (nautical miles) to calculate travel time and ETA. 1 knot = 1.852 km/h, 1 nautical mile = 1.852 km.
Actual travel time may vary due to currents, wind, and sea conditions. Always plan with extra time.
Enter departure time to automatically calculate ETA. Take extra care when planning night passages.
Boat & Marine Calculator - Introduction
Convert distance in nautical miles and cruise speed in knots into hours underway and a calendar ETA. The tool also reports the trip in kilometers and km/h (1 nm = 1.852 km, 1 knot = 1.852 km/h) so you can cross-check chartplotter readings against road-distance intuition.
How It Works
Time (hours) = distance (nautical miles) ÷ speed over ground (knots). The result is decimal hours; the tool splits it into hours and minutes and adds the value to your departure time to produce the ETA. Because the formula uses speed over ground (SOG), not speed through water (STW), it automatically reflects whatever favorable or adverse current you enter into the speed field.
Usage Scenarios
- Coastal day cruise ETA: A 60 nm passage at 15 knots SOG is 60 ÷ 15 = 4.0 hours. Departing at 08:00, you arrive at 12:00 — though most skippers add a 15–30 minute buffer for fuel stops and harbor entry.
- Currents change everything: Same 60 nm passage at 18 knots STW against a 3-knot adverse current means actual SOG is 15 knots and the trip still takes 4 hours, not the 3.3 hours the speedometer would suggest. Always plan with SOG.
- Night passage power budget: An 80 nm overnight run at 6 knots takes 13.3 hours. Combined with your battery runtime, this tells you whether you need to alternate sail and engine to keep house loads supplied until sunrise.
Frequently Asked Questions
How do I convert knots to km/h or mph?
1 knot = 1.852 km/h = 1.151 mph. A boat traveling at 20 knots is going 37 km/h or 23 mph. 1 nautical mile = 1.852 km = 1.151 statute miles.
How do I calculate ETA for a boat trip?
Travel time (hours) = Distance (nautical miles) / Speed (knots). Add departure time to get ETA. For example: 60 nautical miles at 15 knots = 4 hours. Departing at 08:00 means ETA 12:00. Always add buffer time for currents and sea conditions.
How do currents affect navigation calculations?
Currents can significantly affect actual speed over ground. A 2-knot favorable current adds 2 knots to your speed; a 2-knot adverse current subtracts 2 knots. Check tide tables and current charts before departure and adjust your ETA accordingly.
What is the difference between speed over ground and speed through water?
Speed through water (STW) is measured by your boat's speedometer. Speed over ground (SOG) is your actual speed relative to the seabed, accounting for currents. GPS shows SOG. For navigation planning, use SOG for accurate ETAs.
How do I plan a safe night passage?
Plan night passages carefully: check weather forecasts, ensure all navigation lights work, brief crew on watch schedules, identify hazards along the route, and file a float plan with someone ashore. Reduce speed in reduced visibility and maintain a proper lookout.