Speed of Sound Calculator

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.