# Fluid Mechanics - Imperial and SI Units vs. Dimensions

Fluid mechanics in the

- Imperial or USCS - United States Customary Units
- International System of Units - SI system

Terminology | Dimensions | Imperial Units (USCS) | SI-units |
---|---|---|---|

Acceleration due to gravity | L / T^{2} |
ft/s^{2} |
m/s^{2} |

Area | L^{2} |
ft^{2} |
m^{2} |

Chezy roughness coefficient | L^{1/2 }/ T |
ft^{1/2}/s |
m^{1/2}/s |

Critical Depth | L |
ft |
m |

Density | F T^{2}/ L^{4} |
lb s^{2}/ ft^{4}^{ } |
N s^{2}/m^{4} |

Depth | L |
ft |
m |

Depth in open channel | L |
ft |
m |

Diameter | L |
ft |
m |

Distance from solid boundary | L |
ft |
m |

Flow rate | L^{3 }/ T |
ft^{3}/s |
m^{3}/s |

Force | F |
lb |
N |

Force due to pressure | F |
lb |
N |

Hazen Williams roughness coefficient | L^{0.37 }/ T |
ft^{0.37}/s |
m^{0.37}/s |

Head loss due to friction | L |
ft |
m |

Head of height | L |
ft |
m |

Head of weir | L |
ft |
m |

Height above datum | L |
ft |
m |

Hydraulic radius | L |
ft |
m |

Kinematic viscosity | L^{2}/ T |
ft^{2}/s |
m^{2}/s |

Length | L |
ft |
m |

Manning's roughness coefficient | T / L^{1/3} |
s/ft^{1/3} |
s/m^{1/3} |

Mass | F T^{2}/ L |
lb s^{2}/ft |
N s^{2}/m |

Modulus of elasticity | F / L^{2} |
lb/in^{2} (psi) |
Pa |

Perimeter, Weir Height | L |
ft |
m |

Pressure | F / L^{2} |
lb/ft^{2} |
Pa |

Radius | L |
ft |
m |

Shear stress | F / L^{2} |
lb/ft^{2} |
Pa |

Size of roughness | L |
ft |
m |

Specific weight | F / L^{3} |
lb/ft^{3} |
kg/m^{3} |

Surface tension | F / L |
lb/ft |
kg/m |

Time | T |
s |
s |

Thickness | L |
ft |
m |

Time | T |
s |
s |

Total head | L |
ft |
m |

Unit flow rate | L^{3 }/ T L |
ft^{3}/(s ft) |
m^{3}/(s ft) |

Velocity | L / T |
ft/s |
m/s |

Viscosity | F T / L^{2} |
lb s/ft |
Pa s |

Weight | F |
lbf |
N |

*L - length**F - force**T - time*

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