How To Convert Knots to Feet per Second
Formula for 1 unit: 1 knot (kn) = 1.687809857 feet per second (ft/s).
Example: Convert 12 kn to ft/s.
12 × 1.687809857 = 20.253718284 ft/s.
To convert knots to feet per second, you multiply the knot value by 1.687809857.
This works because a knot is based on a nautical mile per hour, and ft/s is feet per second.
If you are doing it by hand, keep the same number of decimals across your steps to avoid rounding errors.
Quick Answer
1 kn = 1.687809857 ft/s
- 5 kn = 8.439049285 ft/s
- 15 kn = 25.317147855 ft/s
- 30 kn = 50.634295710 ft/s
Conversion Formula
ft/s = kn × 1.687809857
This formula means you take a speed in knots and scale it into feet traveled each second.
The number 1.687809857 comes from exact definitions, 1 nautical mile is exactly 1852 meters, 1 hour is exactly 3600 seconds, and 1 foot is exactly 0.3048 meters. Using these fixed standards gives a stable conversion.
- Write your speed in knots.
- Multiply it by 1.687809857.
- The result is the speed in feet per second.
Knot
A knot is a unit of speed equal to one nautical mile per hour. The symbol for knot is kn.
It grew from sea navigation, where sailors measured speed using a log line. It was later standardized using the international nautical mile so everyone could use the same value.
- Ship and boat speed on marine charts
- Wind speed in marine forecasts
- Aircraft speed in aviation
- Tidal and ocean current speeds
- Sailing and racing performance readings
Foot per second
A foot per second is a unit of speed showing how many feet are traveled in one second. The symbol is ft/s.
It is commonly used in engineering and practical measurements in countries that use feet. It is based on the foot, which is fixed as exactly 0.3048 meters.
- Physics and classroom motion problems
- Engineering calculations and testing
- Flow and movement speeds in systems
- Sports and motion tracking reports
- Video analysis where time is measured in seconds
Is this Conversion of Knots To Feet per Second Accurate?
Yes. This conversion uses fixed, internationally accepted definitions. A knot is defined from the international nautical mile, exactly 1852 meters, per hour, and the foot is defined as exactly 0.3048 meters, with the second and hour also precisely defined. Using these constants makes the factor 1 kn = 1.687809857 ft/s reliable for study, engineering calculations, navigation, and general use.
For details on the standards and how we validate conversions, read our accuracy standards.
Real Life Examples
Knots are common on the water and in the air, but ft/s is common in engineering and physics. Here are realistic examples that show both units together.
- Sailboat cruising: A sailboat moving at 18 kn is going 18 × 1.687809857 = 30.380577426 ft/s. That is about 30 feet each second.
- Wind in a coastal forecast: A 25 kn wind equals 25 × 1.687809857 = 42.195246425 ft/s. This helps if your project uses feet and seconds.
- Fast ferry speed: A ferry at 35 kn is 35 × 1.687809857 = 59.073344995 ft/s. This is useful for timing dock approaches in seconds.
- Tidal current planning: A current of 4 kn equals 4 × 1.687809857 = 6.751239428 ft/s. This helps estimate how far you drift during a short maneuver.
- Small aircraft on final approach: 70 kn is 70 × 1.687809857 = 118.146689990 ft/s. Engineers may convert this to ft/s for runway and timing models.
- Storm conditions at sea: 50 kn equals 50 × 1.687809857 = 84.390492850 ft/s. That is a strong wind or fast vessel speed depending on context.
- High altitude winds: 110 kn equals 110 × 1.687809857 = 185.659084270 ft/s. This is useful when comparing with models that use seconds as the time unit.
Quick Tips
- For a fast estimate, use 1 kn ≈ 1.69 ft/s, then refine if you need exact results.
- 10 kn is exactly 16.878098570 ft/s, so you can scale from tens quickly.
- 30 kn is exactly 50.634295710 ft/s, which is a handy reference point.
- If you need knots from ft/s, divide by 1.687809857.
- Keep extra decimals during the math, then round only at the end.
- Always check that your inputs are speed, not distance or acceleration.