Sound Speed in Water Calculator
Sound travels about 1,482 m/s in fresh water at 20 °C and about 1,507 m/s in seawater at 15 °C and 35 ppt. Speed rises about 2–4.6 m/s per °C (most in cold water), 1.3 m/s per ppt of salinity and 1.6–1.7 m/s per 100 m of depth.
Use the Sound Speed in Water Calculator
Water & Equation
Each equation is used only inside its published range.
Open ocean ≈ 35 ppt; Baltic ≈ 7; brackish estuaries 0.5–30 (use UNESCO or Coppens below 25).
Sources: UK NPL seawater equations (UNESCO, Mackenzie, Coppens, Leroy & Parthiot), Lubbers & Graaff (1998), Marczak (1997) J. Acoust. Soc. Am. 102, 2776, and NIST SP 811.
Speed of sound in water by temperature (surface pressure)
Fresh water: Marczak (1997). Seawater 35 ppt: UNESCO / Wong & Zhu (1995), valid to 40 °C.
| Temp | Fresh m/s | Fresh ft/s | Seawater m/s | Seawater ft/s |
|---|---|---|---|---|
| 0 °C (32 °F) | 1,402.4 | 4,601 | 1,449.1 | 4,754 |
| 4 °C (39 °F) | 1,421.6 | 4,664 | 1,466.6 | 4,812 |
| 5 °C (41 °F) | 1,426.2 | 4,679 | 1,470.7 | 4,825 |
| 10 °C (50 °F) | 1,447.3 | 4,748 | 1,489.8 | 4,888 |
| 15 °C (59 °F) | 1,466.0 | 4,810 | 1,506.7 | 4,943 |
| 20 °C (68 °F) | 1,482.4 | 4,863 | 1,521.5 | 4,992 |
| 25 °C (77 °F) | 1,496.7 | 4,911 | 1,534.4 | 5,034 |
| 30 °C (86 °F) | 1,509.2 | 4,951 | 1,545.6 | 5,071 |
| 35 °C (95 °F) | 1,519.8 | 4,986 | 1,555.2 | 5,102 |
| 40 °C (104 °F) | 1,528.9 | 5,016 | 1,563.2 | 5,129 |
| 50 °C (122 °F) | 1,542.6 | 5,061 | — | — |
| 60 °C (140 °F) | 1,551.0 | 5,089 | — | — |
| 74 °C (165 °F) | 1,555.1 | 5,102 | — | — |
| 80 °C (176 °F) | 1,554.5 | 5,100 | — | — |
| 90 °C (194 °F) | 1,550.5 | 5,087 | — | — |
Worked examples
Ocean surface. T = 15 °C, S = 35 ppt, D = 0: UNESCO 1,506.68 m/s, Mackenzie 1,506.69 m/s, Coppens 1,506.65 m/s.
1,000 m deep, 4 °C. Pressure at 45° latitude is 100.9 bar (Leroy & Parthiot). UNESCO gives 1,483.23 m/s, Mackenzie 1,482.96 m/s and Coppens 1,483.02 m/s; about 23 m/s slower than the surface despite the higher pressure, because the water is 11 °C colder.
Fresh water. 20 °C: Marczak 1,482.38 m/s, Lubbers & Graaff 1,482.30 m/s. A 40 ms echo at 1,482.4 m/s is 29.65 m away.
Summary
The speed of sound in water depends on temperature, salinity and pressure (depth). This calculator offers the standard published equations and labels which one produced each result: for seawater the UNESCO algorithm of Chen and Millero as refitted by Wong and Zhu (1995) for ITS-90, the nine-term Mackenzie (1981) equation and the Coppens (1981) equation; for fresh water the Marczak (1997) fit valid from 0 to 95 °C and the Lubbers & Graaff (1998) equation for 15–35 °C. Depth is converted to pressure for the UNESCO equation with the Leroy and Parthiot (1998) formula at your latitude. A comparison table shows every equation side by side, and the result feeds an echo-sounder range and wavelength helper.
How it works
- Pick seawater or fresh water, then the equation. Each equation is only evaluated inside its published validity range.
- Enter temperature (°C or °F), and for seawater salinity (ppt or PSU), depth (m or ft) and, for UNESCO, latitude.
- UNESCO: c = Cw(T,P) + A(T,P)·S + B(T,P)·S^1.5 + D(T,P)·S², with pressure in bar from depth by Leroy & Parthiot (1998).
- Mackenzie (1981): c = 1448.96 + 4.591T − 0.05304T² + 0.0002374T³ + 1.340(S − 35) + 0.0163D + 1.675×10⁻⁷D² − 0.01025T(S − 35) − 7.139×10⁻¹³TD³.
- Fresh water, Marczak (1997): c = 1402.385 + 5.038813T − 5.799136×10⁻²T² + 3.287156×10⁻⁴T³ − 1.398845×10⁻⁶T⁴ + 2.787860×10⁻⁹T⁵.
- Range from an echo: distance = c × two-way travel time ÷ 2. Wavelength = c ÷ frequency.
Use cases
- Set the sound velocity for an echo sounder, sonar, ADCP or acoustic modem from a temperature and salinity reading.
- Convert two-way travel time to depth or range.
- Find the speed of sound in fresh water for ultrasonic flow meters, tank level sensors and lab transducers, including hot water up to 95 °C.
- Compare UNESCO, Mackenzie and Coppens results to see the spread between standard equations.
- Teach how temperature, salinity and pressure each change underwater sound speed.