Sailing Distance & ETA Calculator
Enter your start and destination coordinates to estimate great-circle distance, route-adjusted distance, and travel time based on average speed.
Why this bednblue sailing distance calculator is useful
Passage planning starts with one practical question: How far is it, really? For sailors, the answer is not as simple as drawing a straight line on a map. Wind angle, current, sea state, and safe routing decisions can all stretch your trip. This calculator gives you a quick baseline using geographic coordinates and then lets you adjust with route efficiency for more realistic estimates.
Whether you are preparing for a coastal hop, a weekend island crossing, or initial planning for an offshore leg, this tool helps you compare routes, estimate fuel and provisions, and build a better departure window.
How the calculator works
1) Great-circle distance
The base distance is computed with the haversine formula, which estimates the shortest path over Earth’s surface between two latitude/longitude points. This is commonly used in marine and aviation routing as a first-pass distance.
2) Route efficiency adjustment
Most sailboats do not follow the exact shortest path. If your upwind angles force tacking, or if weather requires a diversion, your sailed track will be longer. Route efficiency lets you account for this:
- 100%: ideal direct route.
- 90%: moderate extra distance.
- 80–85%: more complex routing and additional maneuvering.
3) ETA from speed in knots
After adjusted distance is calculated, the script estimates travel time using your entered average speed in knots (nautical miles per hour). The result is shown in hours and in day/hour/minute format for easier trip planning.
What to enter for best results
- Latitude/Longitude: Use decimal degrees from your chartplotter, nav app, or chart source.
- Average speed: Use realistic trip-average speed, not peak speed.
- Efficiency: Start at 90%, then lower it if the route is likely to be upwind or constrained by traffic schemes and hazards.
Suggested planning workflow
Before departure
- Calculate baseline and adjusted distances.
- Run optimistic and conservative speed scenarios.
- Check daylight arrival options and tide/current timing.
During route selection
- Compare alternate waypoints and expected headings.
- Review weather windows and wave direction.
- Recalculate if your expected average speed changes.
Important limitations
This calculator is a planning aid, not a substitute for full navigation. Always verify with updated charts, notices to mariners, weather forecasts, and onboard seamanship practices. Real-world factors that can significantly change passage time include:
- Strong adverse current or wind shifts
- No-go zones, shoals, and exclusion areas
- Traffic separation schemes and local regulations
- Night approach constraints and harbor wait times
Quick takeaway
The bednblue sailing distance calculator gives you a fast, practical answer to distance and ETA using coordinate-based math and sailor-friendly adjustments. Use it early in planning, rerun it as forecasts change, and pair it with sound navigation judgment for safer, more predictable passages.