Speed Distance Time Calculator
Solve for speed, distance or time — enter any two values to calculate the third. Uses nautical miles and knots.
Results are planning estimates. Verify navigation, weather, vessel and operational information using appropriate professional sources.
What Is the Speed Distance Time Calculator?
The speed-distance-time (SDT) relationship is fundamental to navigation. Given any two of the three values, you can calculate the third. This calculator uses nautical miles and knots, making it directly applicable to maritime passage planning. The same formula applies to any constant-speed scenario.
How to Use the Speed Distance Time Calculator
- Select which value you want to calculate (speed, distance or time).
- Enter the other two known values.
- Click Calculate.
Formula
Worked Example
Distance: 200 nmi, Time: 16h 40min (16.667h)
Speed = 200 ÷ 16.667 = 12 knots
Speed: 12 knots, Time: 16h 40min
Distance = 12 × 16.667 = 200 nmi
Understanding Your Result
The SDT triangle is a core navigation concept. In practice, vessels rarely maintain perfectly constant speed, so these calculations give planning estimates. Always apply appropriate safety margins for weather, current and operational factors.
Common Mistakes
- Mixing units — ensure speed is in knots and distance is in nautical miles.
- Using total time including port time — use only the time underway at sea.
Frequently Asked Questions
Can I use this for km/h and kilometres?
Yes — the formula is the same regardless of units. Just ensure speed and distance use consistent units (both metric or both nautical).
What is the "60D ST" rule?
A traditional navigation shortcut: Distance = Speed × Time ÷ 60 (when time is in minutes). For example, at 12 knots for 30 minutes: 12 × 30 ÷ 60 = 6 nautical miles.