Bulk modulus and density reveal how fast pressure waves travel through media. Use flexible units, instant graphs, and exports for laboratory reports every time.
For a fluid (or an effective bulk response), the longitudinal sound speed is:
For solids, actual wave speed depends on elastic moduli and mode. This tool uses the bulk-modulus form as a practical estimate.
| Material | Bulk Modulus | Density | Estimated v (m/s) |
|---|---|---|---|
| Water (20°C) | 2.2 GPa | 998 kg/m³ | 1,484.73 |
| Air (20°C) | 0.000142 GPa | 1.204 kg/m³ | 343.42 |
| Steel (approx.) | 160 GPa | 7850 kg/m³ | 4,514.66 |
| Glass (soda-lime) | 35 GPa | 2500 kg/m³ | 3,741.66 |
| Granite | 50 GPa | 2700 kg/m³ | 4,303.31 |
The bulk modulus K measures how strongly a material resists uniform compression. A larger K means the medium is less compressible, so a pressure disturbance propagates more rapidly. In fluids, where shear stiffness is negligible, K is the key elastic property controlling acoustic wave speed.
Density ρ sets the inertial “load” that the pressure wave must accelerate. For the same bulk modulus, doubling ρ reduces the speed by a factor of √2. This is why light gases can carry sound faster than you might expect when their compressibility is also low under pressure.
Small-amplitude acoustics couples conservation of mass with a linear pressure–density relation. If the medium’s compressibility is captured by K, the wave equation yields v = √(K/ρ). The calculator applies this directly after converting your chosen units into SI for consistent computation.
At room conditions, air has an effective bulk modulus near 1.4×105 Pa and density about 1.2 kg/m³, giving roughly 343 m/s. Liquid water has K ≈ 2.2 GPa and ρ ≈ 1000 kg/m³, producing about 1480 m/s. These benchmarks help you sanity-check inputs quickly.
In solids, longitudinal sound speed depends on both compressibility and shear rigidity. A better model uses vL = √((K + 4G/3)/ρ), where G is shear modulus. Using only K can underpredict the true longitudinal speed for metals, ceramics, and composites.
Many materials change K and ρ with temperature, while gases also depend strongly on pressure and heat-capacity ratio. For air, warmer temperatures lower density and generally increase speed. For liquids, higher pressure often increases K, slightly raising sound speed in high-pressure systems.
Bulk modulus can be obtained from compressibility tests, ultrasonic measurements, or tabulated thermophysical properties. Density is usually measured by mass/volume methods or provided in datasheets. When combining data from different references, ensure they correspond to the same temperature, composition, and state.
Accurate sound-speed estimates support pipe acoustics, water-hammer analysis, sonar and ultrasound design, material screening, and quality control. If your computed value looks unrealistic, re-check unit selections and confirm that K represents the appropriate “effective” modulus for your medium and conditions.
Compressibility is the inverse of bulk modulus. A high bulk modulus means low compressibility, so the medium resists volume change and transmits pressure waves faster.
It can provide a rough estimate, but solids require shear modulus too. For longitudinal waves in solids, use vL = √((K + 4G/3)/ρ) when you have G.
Most issues come from unit mismatches or unrealistic property values. Verify that K and ρ are in compatible units, and that they correspond to the same temperature and material state.
For small, rapid sound waves in a gas, the effective modulus is often the adiabatic bulk modulus, not the isothermal one. Using the wrong modulus can shift results noticeably.
In gases like air, higher temperature generally increases sound speed. In liquids and solids, the trend can vary because both elasticity and density change with temperature.
A common reference is K ≈ 2.2 GPa and ρ ≈ 1000 kg/m³, which gives a speed close to 1480 m/s. Salinity and temperature shift this value.
Convert compressibility β to bulk modulus using K = 1/β, then compute v = √(K/ρ). Ensure β is in 1/Pa (or equivalent) before converting.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.