Converting Common Measurement Units to SI

Corrections have been made to area, volume, temperature, water-column and power conversions in the older table. A dot is the decimal separator and a comma separates thousands. The symbol ≈ denotes a rounded value.

1. Length

• 1 in = 0.0254 m
• 1 ft = 0.3048 m
• 1 yard = 0.9144 m
• 1 mile = 1,609.344 m

2. Speed

• 1 mph = 0.44704 m/s
• 1 ft/min = 0.00508 m/s
• 1 km/h ≈ 0.277778 m/s

3. Area

• 1 in² = 0.00064516 m²
• 1 ft² = 0.09290304 m²

4. Mass

• 1 lb = 0.45359237 kg
• 1 Zentner = 50 kg
• 1 grain ≈ 64.79891 × 10⁻⁶ kg
• 1 long ton ≈ 1,016.047 kg
• 1 short ton ≈ 907.1847 kg

5. Force

• 1 dyn = 10⁻⁵ N
• 1 kgf = 9.80665 N

6. Pressure

• 1 kgf/cm² = 1 at = 98,066.5 Pa = 0.980665 bar
• 1 bar = 100,000 Pa
• 1 mbar = 100 Pa
• 1 atm = 101,325 Pa = 1.01325 bar
• 10 mH₂O = 1 at = 0.980665 bar
• 760 mmHg ≈ 1 atm
• 750 mmHg ≈ 1 bar
• 559 mmHg ≈ 1 at
• 1 mmHg ≈ 133.3224 Pa; 1 Torr = 101,325/760 Pa
• 1 Pa = 1 N/m²
• 1 psi ≈ 6,894.757 Pa = 0.06894757 bar
• 1 inHg ≈ 3,386.389 Pa
• 1 inH₂O ≈ 249.0889 Pa

7. Specific heat capacity

• 1 kcalIT/(kg·K) = 4,186.8 J/(kg·K)
• 1 BtuIT/(lb·°F) = 4,186.8 J/(kg·K)

8. Temperature

• t(°C) = [t(°F) − 32] × 5/9
• t(°F) = t(°C) × 9/5 + 32
• T(K) = t(°C) + 273.15

9. Volume and volumetric flow

• 1 in³ = 0.000016387064 m³
• 1 ft³ = 0.028316846592 m³
• 1 Imperial gallon = 0.00454609 m³
• 1 US liquid gallon ≈ 0.003785412 m³
• 1 US dry gallon ≈ 0.004404884 m³
• 1 US bushel ≈ 0.03523907 m³
• 1 ft³/lb ≈ 0.06242796 m³/kg
• 1 ft³/min ≈ 0.0004719474 m³/s

10. Work and heat

• 1 kWh = 3,600 kJ
• 1 kgf·m = 9.80665 J
• 1 kcalIT = 4,186.8 J
• 1 BtuIT ≈ 1,055.056 J
• 1 BtuIT/lb = 2,326 J/kg

11. Power and heat flow rate

• 1 kgf·m/s = 9.80665 W
• 1 PS ≈ 735.4988 W
• 1 hp ≈ 745.6999 W
• 1 kcalIT/h = 1.163 W
• 1 BtuIT/h ≈ 0.2930711 W
• 1 USRT = 12,000 BtuIT/h ≈ 3,516.853 W ≈ 3,023.949 kcalIT/h

12. Thermal conductivity

• 1 kcalIT/(m·h·K) = 1.163 W/(m·K)
• 1 BtuIT·in/(h·ft²·°F) ≈ 0.1442279 W/(m·K)
• 1 BtuIT/(h·ft·°F) ≈ 1.730735 W/(m·K)

13. Kinematic viscosity

• 1 cSt = 10⁻⁶ m²/s
• 1 ft²/h = 25.8064 × 10⁻⁶ m²/s
• 1 ft²/s = 0.09290304 m²/s

Conventions and older units

IT denotes the International Table convention for calories and Btu. Kilogram-force (kgf) is a force unit, distinct from kilogram mass. Fluid-column values use conventional standard definitions. Zentner here follows the 50 kg convention. The older table also gives IRT = 4,186 W and IKT = 3,860 W without a clear definition; do not apply these two factors without checking the equipment documentation.

Reference: NIST — Guide to the SI, Appendix B.8