PhysicalConstants is a Julia package which has the values of a range of physical constants. Currently MKS and CGS units are supported.
The package can be installed directly from its github repository:
Pkg.clone("https://github.com/DataWookie/PhysicalConstants.jl")
Usage is pretty straightforward. Start off by loading the package.
julia> using PhysicalConstants
Now access Earth's gravitational acceleration in MKS units.
julia> PhysicalConstants.MKS.GravAccel
9.80665
Or in CGS units.
julia> PhysicalConstants.CGS.GravAccel
980.665
Of finally, in Imperial units.
julia> PhysicalConstants.Imperial.GravAccel
32.174049