Foot per Second to Velocity of Sound in Sea Water (20°C, 10m depth)

Foot per second measures the number of feet traveled in one second. Commonly used in engineering, ballistics, and some sports in the United States.

1 ft/s = 0.3048 m/s exactly (by definition of the international foot). 1 ft/s = 0.6818 mph.

To m/s: × 0.3048. To km/h: × 1.097. To mph: × 0.682. To knots: × 0.592.

Bullet velocities (handgun: 800–1,200 ft/s; rifle: 2,500–4,000 ft/s), waterfall flow rates, industrial conveyor speeds, and skydiving terminal velocity (120 ft/s).

Speed of sound: 1,125 ft/s at sea level. Free fall: 32 ft/s² acceleration. Skydiver terminal velocity: 120 ft/s. Baseball pitch: 132 ft/s (90 mph).

Confusing ft/s with mph — 1 ft/s is only 0.68 mph, not 1 mph. Also, mixing up ft/s and ft/min in HVAC calculations.

1 ft/s ≈ 0.3 m/s or ≈ 1.1 km/h. Quick check: 100 ft/s ≈ 70 mph. Multiply ft/s by 0.68 for approximate mph.

The speed of sound in seawater at 20°C and 10 meters depth is approximately 1,522 m/s, varying with temperature, salinity, and pressure.

Complex function of T, S, P. Mackenzie equation: c ≈ 1,449 + 4.6T - 0.055T² + 0.00029T³ + (1.34-0.01T)(S-35) + 0.016z. Typical: ~1,500 m/s.

To km/h: × 3.6. To ft/s: × 3.281. 1,522 m/s = 5,479 km/h = 3,404 mph.

Naval sonar, commercial ship echo sounders, underwater positioning systems, and marine seismic surveys.

Sound speed increases ~1.3 m/s per °C, ~1.3 m/s per PSU salinity, and ~1.7 m/s per 100m depth. SOFAR channel at ~1000m depth traps sound for thousands of km.

Using a single constant — sound speed in the ocean varies significantly with depth and location. Always measure or calculate for local conditions.

~1,500 m/s is a good approximation. Remember: warmer, saltier, deeper = faster sound. Critical for accurate sonar ranging.