# Fluid Mechanics - Imperial and SI Units Dimensions

## Imperial (USCS) and SI dimensions and units terminology in fluid mechanics

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*