Estimate nautical fuel efficiency, trip duration, and fuel cost for a boat or ship voyage.
What is a sea mileage calculator?
A sea mileage calculator helps you measure how efficiently a vessel uses fuel over water routes. Unlike road calculations that focus on miles per gallon, marine planning often uses nautical miles and knots. This tool converts units automatically and gives you a clear view of fuel efficiency, consumption rate, and estimated trip cost.
If you operate a fishing boat, yacht, ferry, or workboat, even small improvements in fuel performance can produce meaningful savings over time.
How to use this calculator
1) Enter route distance
Add the planned or completed trip distance. You can enter nautical miles, statute miles, or kilometers.
2) Enter total fuel used
Input fuel consumed for that leg of travel. Select liters, US gallons, or imperial gallons.
3) Add optional cost and speed
- Fuel price: used to estimate total fuel expense.
- Average speed (knots): used to estimate trip duration.
Core marine efficiency metrics
The calculator reports several useful outputs so you can compare voyages consistently:
- Nautical miles per liter: how far you travel per liter of fuel.
- Nautical miles per US gallon: common benchmark for many operators.
- Liters per 100 nautical miles: easy way to model fuel burn for longer routes.
- MPG (statute, US): familiar conversion for mixed marine-road comparisons.
Why nautical miles and knots matter
Marine navigation uses nautical miles because they align with latitude/longitude and charting systems. One knot equals one nautical mile per hour. Working directly in nautical units makes route planning, timing, and communication with crew and port services more accurate and efficient.
What affects sea mileage the most?
Hull and propeller condition
Marine growth, rough paint, or propeller damage can increase drag and fuel burn quickly.
Sea state and weather
Wind, swell, current, and wave angle can change consumption significantly, especially on smaller vessels.
Speed profile
Running just above the vessel’s most efficient cruising speed often causes a steep increase in fuel use.
Loading and trim
Uneven weight distribution and excess cargo both reduce efficiency. Correct trim can improve mileage immediately.
Practical trip-planning tips
- Log fuel and distance for every trip in the same units.
- Track efficiency by route and weather conditions.
- Set a reserve fuel margin for safety and unexpected headwinds.
- Compare performance before and after maintenance.
- Use this calculator to estimate cost scenarios before departure.
Example scenario
If a vessel travels 180 nautical miles and consumes 95 liters, the efficiency is about 1.89 nm/L and roughly 52.8 L per 100 nm. If fuel costs $1.70 per liter, trip fuel cost is approximately $161.50. At an average speed of 15 knots, travel time is about 12 hours.
Final note
Use this sea mileage calculator as a planning and benchmarking tool, not as a substitute for onboard fuel management, weather routing, or safety protocols. For the best results, combine calculated estimates with real voyage logs and maintenance records.