Specific Weight of Water Units — N/m³, lbf/ft³, kN/m³ Reference Table
Complete reference for the specific weight of water units used in engineering — γ_water in SI (N/m³, kN/m³), in US imperial (lbf/ft³), and the temperature-dependent values 0–100 °C. Covers the specific weight of water in SI unit and the equivalent specific weight of water in si units phrasing, the imperial specific weight of water imperial value, the specific unit weight definition, and the related specific heat capacity calculator workflow. Reviewed by a licensed PE.
Tools and conversions
For the specific weight of water units conversion: 1 lbf/ft³ = 157.087 N/m³. So 62.43 lbf/ft³ × 157.087 ≈ 9 807 N/m³, matching the SI value. We don\'t yet host a dedicated water-specific-weight widget; for now use the formula card below or the table further down. Related computational tools: specific gravity calculator for the dimensionless cousin, and duct sizing calculator for fluid-flow applications.
The water specific-weight formula
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- γ_water = specific weight of water (N/m³)
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- ρ_water = density of water (kg/m³); 1 000 at 4 °C, 998.2 at 20 °C
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- g = standard gravity 9.80665 m/s²
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- 1 lbf/ft³ = 157.087 N/m³ exactly
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- 9 810 N/m³ ÷ 157.087 = 62.43 lbf/ft³
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- 62.43 lbf/ft³ × 157.087 = 9 807 N/m³
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- P = pressure at depth h (Pa = N/m²)
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- h = depth below the free surface (m)
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- 10 m of water = 9 810 × 10 = 98.1 kPa ≈ 1 atm
Standards and reference data
| Standard / source | Scope |
|---|---|
| BIPM SI 9th Edition (2019) | Definition of mass, length, time, and standard gravity |
| NIST SP 811 | Authoritative SI unit conversion tables — including γ in N/m³ ↔ lbf/ft³ |
| IAPWS-IF97 | Industrial Formulation for Water and Steam — temperature-dependent properties (ρ, γ, c_p, μ) |
| ASTM D1193 | Reference reagent water — purity standards used in laboratory γ measurements |
| ISO/IEC 17025 | General requirements for testing and calibration laboratories handling water-property measurement |
Reference: γ_water by temperature
Pure-water values at 1 atm pressure and standard gravity g = 9.80665 m/s². Use IAPWS-IF97 for higher precision in steam-cycle work.
| Temperature (°C) | Density ρ (kg/m³) | γ_water (N/m³) | γ_water (kN/m³) | γ_water (lbf/ft³) |
|---|---|---|---|---|
| 0 (ice) | 917 | 8 994 | 8.99 | 57.24 |
| 0 (liquid) | 999.84 | 9 805 | 9.81 | 62.41 |
| 4 (max density, std ref) | 1 000.00 | 9 807 | 9.81 | 62.43 |
| 10 | 999.7 | 9 804 | 9.80 | 62.41 |
| 20 | 998.2 | 9 789 | 9.79 | 62.32 |
| 25 | 997.0 | 9 778 | 9.78 | 62.25 |
| 30 | 995.6 | 9 764 | 9.76 | 62.16 |
| 40 | 992.2 | 9 731 | 9.73 | 61.95 |
| 50 | 988.0 | 9 689 | 9.69 | 61.69 |
| 60 | 983.2 | 9 642 | 9.64 | 61.39 |
| 70 | 977.7 | 9 588 | 9.59 | 61.05 |
| 80 | 971.6 | 9 528 | 9.53 | 60.66 |
| 90 | 965.1 | 9 465 | 9.47 | 60.26 |
| 100 (boiling at 1 atm) | 958.4 | 9 399 | 9.40 | 59.84 |