What this calculator does
This calculator gives the speed of sound in pure (distilled) water at atmospheric pressure as a function of temperature. Enter a temperature between 0 °C and 95 °C (32–203 °F) and it returns the sound speed in metres per second, together with conversions to kilometres per hour, feet per second and miles per hour.
The calculation uses the fifth-degree polynomial published by W. Marczak in 1997 in the Journal of the Acoustical Society of America, a widely used reference correlation fitted to high-precision experimental measurements of sound speed in pure water. Within its stated validity range of 0–95 °C it fits the underlying experimental data to well under 0.1 m/s. For reference, sound travels at about 1,482.4 m/s in water at 20 °C and about 1,496.7 m/s at 25 °C.
How to use it
- Enter the water temperature in the first field.
- Choose the temperature unit: Celsius (°C) or Fahrenheit (°F). Fahrenheit inputs are converted to Celsius before the correlation is applied.
- Press Calculate. The main result is the speed of sound in metres per second; the table below it shows the same speed in km/h, ft/s and mph.
Keep in mind the assumptions: the correlation applies to pure water at atmospheric pressure. It is not valid for seawater (salinity raises the sound speed) or for deep-water conditions where pressure matters, and the temperature must stay within 0–95 °C.
The formula explained
The calculator evaluates Marczak’s (1997) five-degree polynomial, where c is the speed of sound in m/s and T is the water temperature in °C:
$$c(T) = 1402.385 + 5.038813\,T - 5.799136 \times 10^{-2}\,T^{2} + 3.287156 \times 10^{-4}\,T^{3} - 1.398845 \times 10^{-6}\,T^{4} + 2.787860 \times 10^{-9}\,T^{5}$$Source: W. Marczak, “Water as a standard in the measurements of speed of sound in liquids”, Journal of the Acoustical Society of America, 102(5), 2776–2779 (1997). Validity: 0 ≤ T ≤ 95 °C at atmospheric pressure.
The curve is not monotonic: the speed rises from about 1,402.4 m/s at 0 °C, reaches a maximum of roughly 1,555 m/s near 74 °C, and then decreases slightly as the temperature approaches 95 °C.
Worked example
What is the speed of sound in pure water at 25 °C? Substituting T = 25 into the polynomial, term by term:
- Constant term: 1402.385
- 5.038813 × 25 = +125.970325
- 5.799136 × 10−2 × 25² = 0.05799136 × 625 = −36.244600
- 3.287156 × 10−4 × 25³ = 0.0003287156 × 15,625 = +5.136181
- 1.398845 × 10−6 × 25⁴ = 0.000001398845 × 390,625 = −0.546424
- 2.787860 × 10−9 × 25⁵ = 0.00000000278786 × 9,765,625 = +0.027225
So at 25 °C, sound travels through pure water at about 1,496.73 m/s — roughly 5,388 km/h or 3,348 mph.
Frequently asked questions
Why does sound travel faster in water than in air? The speed of sound in a fluid equals the square root of the bulk modulus divided by the density. Water is far less compressible than air, and that stiffness outweighs its higher density, so sound moves about 4.3 times faster in water — roughly 1,482 m/s versus about 343 m/s in air at 20 °C.
Does the speed of sound in water always increase with temperature? No. Unusually among liquids, it increases from about 1,402.4 m/s at 0 °C up to a maximum of roughly 1,555 m/s near 74 °C, then slowly decreases as the water gets hotter. This calculator reproduces that non-monotonic behaviour because it uses the full fifth-degree polynomial rather than a linear approximation.
Can I use this calculator for seawater? No. Salinity raises the sound speed by roughly 1.3 m/s per practical salinity unit, and pressure adds more with depth, so ocean sound speeds are typically some tens of metres per second higher than in pure water. For seawater, dedicated correlations such as Mackenzie (1981) or the Chen–Millero (UNESCO) equation should be used instead.
