Fluid Mechanics - Imperial and SI Units vs. Dimensions

Imperial (USCS) and SI dimensions and units terminology in fluid mechanics. Reference guide for converting between Imperial/USCS and SI units across various fluid mechanics parameters.

Terminology	Dimensions	Imperial Units (USCS)	SI Units
Acceleration due to gravity	L / T²	ft/s²	m/s²
Area	L²	ft²	m²
Chezy roughness coefficient	L^(1/2) / T	ft^(1/2)/s	m^(1/2)/s
Critical Depth	L	ft	m
Density	F T² / L⁴	lb s² / ft⁴	N s²/m⁴
Depth	L	ft	m
Depth in open channel	L	ft	m
Diameter	L	ft	m
Distance from solid boundary	L	ft	m
Flow rate	L³ / T	ft³/s	m³/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	L² / T	ft²/s	m²/s
Length	L	ft	m
Manning's roughness coefficient	T / L^(1/3)	s/ft^(1/3)	s/m^(1/3)
Mass	F T² / L	lb s²/ft	N s²/m
Modulus of elasticity	F / L²	lb/in² (psi)	Pa
Perimeter, Weir Height	L	ft	m
Pressure	F / L²	lb/ft²	Pa
Radius	L	ft	m
Shear stress	F / L²	lb/ft²	Pa
Size of roughness	L	ft	m
Specific weight	F / L³	lb/ft³	kg/m³
Surface tension	F / L	lb/ft	kg/m
Time	T	s	s
Thickness	L	ft	m
Total head	L	ft	m
Unit flow rate	L³ / (T L)	ft³/(s ft)	m³/(s m)
Velocity	L / T	ft/s	m/s
Viscosity	F T / L²	lb s/ft²	Pa s
Weight	F	lbf	N