Speed Over Ground Calculator — Examples
Updated recently with improved calculation accuracy and expanded examples.
Vector sum of speed through water and current using law of cosines.
Last updated: April 22, 2026
Author: OceanCalc Editorial Team · Publisher: Albor Digital LLC
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Explore typical numbers with the Speed Over Ground Calculator. Try the examples in the Examples section below while you vary inputs in the calculator.
Speed Over Ground Calculator
Result
Speed over ground (kn)
7.14
Formula
SOG = √(STW² + Vc² + 2·STW·Vc·cos θ)Ad slot — after calculation result
Use this calculation together with proper navigation tools to improve route accuracy and on-water decision making.
What is the Speed Over Ground Calculator?
Vector sum of speed through water and current using law of cosines.
knot
A knot is a unit of speed equal to one nautical mile per hour (1.852 km/h). Marine wind, boat speed, and current are usually given in knots.
Related Maritime Calculators
Overview
A knot is a unit of speed equal to one nautical mile per hour (1.852 km/h). A Speed Over Ground Calculator is used in maritime navigation to perform precise calculations based on established nautical formulas. This tool allows you to apply your inputs to the stated nautical relationships using accurate and standardized methods.
Key takeaways
- Speed Over Ground Calculator — A knot is a unit of speed equal to one nautical mile per hour (1.852 km/h).
- Formula — θ is the angle between velocity vectors of boat through water and water movement (set).
- How to use — Enter numbers in the fields above; results update as you change inputs.
Recommended Marine Navigation Tools
These tools are commonly used alongside navigation calculations for real-world sailing and route planning.
- Marine Navigation Parallel Ruler — used for plotting bearings on nautical charts
- Handheld GPS Navigator — provides real-time position and course tracking at sea
- Nautical Chart Plotter Kit — essential for route planning and distance measurement
These are optional tools used by sailors and marine professionals. Choose based on your navigation setup.
How to use
Enter numbers in the fields above; results update as you change inputs.
Formula
Core relationship: SOG = √(STW² + Vc² + 2·STW·Vc·cos θ)
θ is the angle between velocity vectors of boat through water and water movement (set).
Practical use cases
Speed Over Ground Calculator: passage planning, crew briefings, instrument-to-chart unit checks, and verifying mental math when tired or in rough weather.
Tips for accuracy
- Match input units to your chart, GPS, or instrument before trusting the Speed Over Ground Calculator.
- Cross-check important outputs with a second method or crew when visibility or motion is poor.
- Treat simplified models (waves, radar horizon, etc.) as estimates; real conditions vary.
Practical examples
- 6 kn STW + 1.5 kn current at 45° → ~7.1 kn SOG (illustrative)
Frequently Asked Questions
How accurate is this calculator?
It uses standard maritime formulas and noted approximations. Use it for planning and checks; confirm safety-critical decisions with official sources.
Can I use this on mobile?
Yes. Layouts are responsive for phones and tablets on deck or in the cockpit.
Related Navigation Calculations
- Calculate maximum hull speed based on waterline length
- Compute rhumb line distance for constant bearing navigation
- Find initial bearing between two geographic coordinates
- Estimate visual horizon distance based on observer height
- Measure deviation from intended navigation path
- Calculate actual vessel speed considering current and heading
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When to Use This Calculation
- • Planning a navigation route between two points
- • Adjusting course based on wind, current, or drift
- • Verifying distances and bearings during passage planning
- • Supporting manual navigation alongside GPS systems
Explore more
Popular calculators: Nautical Mile Converter · Knots to km/h Converter · Hull Speed Calculator · Initial Bearing Calculator · Great Circle Distance Calculator · Boat Fuel Consumption Calculator · VMG Calculator
These calculations are based on standard maritime navigation formulas used in seamanship, chart navigation, and marine route planning.
Results are estimates for educational purposes only and should not be used for real navigation decisions.
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