Speed of Sound Calculator
Calculate the speed of sound in air, water, or steel at any temperature.
Includes unit conversion between m/s, ft/s, mph, and km/h.
Speed of sound in air changes with temperature because warmer air molecules move faster and transmit pressure waves more quickly. The relationship is approximately linear over normal temperature ranges — every 1°C increase raises the speed of sound by about 0.6 m/s.
Speed of sound in air formula: v = 331.3 × √(1 + T/273.15) m/s
Or the simplified linear approximation (valid from −20°C to +40°C): v ≈ 331.3 + 0.606 × T (m/s)
Where:
- v = speed of sound in meters per second
- T = air temperature in degrees Celsius
- 331.3 m/s = speed of sound at 0°C (273.15 K)
- 0.606 = approximate rate of change per °C
Converting to other units:
- 1 m/s = 3.281 ft/s
- 1 m/s = 2.237 mph
- Mach 1 = speed of sound at current conditions
Speed of sound at common temperatures:
- −20°C (−4°F): 318.8 m/s (703 mph)
- 0°C (32°F): 331.3 m/s (741 mph)
- 20°C (68°F): 343.2 m/s (767 mph) ← standard atmosphere
- 30°C (86°F): 349.1 m/s (781 mph)
- 40°C (104°F): 354.9 m/s (794 mph)
Effect of humidity: Humidity slightly increases the speed of sound (water vapor is lighter than nitrogen/oxygen). At 100% relative humidity, speed increases by about 0.1–0.4% — a negligible effect for most practical purposes.
Worked example: A thunderstorm occurs on a summer day at 28°C. You see lightning and hear thunder 5 seconds later.
- Speed of sound at 28°C: 331.3 + (0.606 × 28) = 331.3 + 16.97 = 348.3 m/s
- Distance to lightning = 348.3 m/s × 5 s = 1,741 meters = 1.74 km (~1.1 miles)
The common rule “5 seconds = 1 mile” is approximate and most accurate near 20°C. At 28°C, 5 seconds corresponds to about 1.08 miles.