How does the magnetic field at the centre of a current-carrying coil change when the radius of the coil is halved while keeping other parameters constant?

The magnetic field in the centre of a circular coil may be calculated as follows:

B=μ0I2R
Where B is the magnetic field at the centre of the coil, μ0 is the permeability of free space =4π×10-7
I is the current and R is the radius of the circular coil.

The new magnetic field B' in the centre of a circular coil when the radius is reduced to half will be given as:B'=μ0I2R' now R' = R2 then, 

B'=μ0I2R2= 2(μ0I2R) 

B'=2B

Therefore, when the radius is halved, the magnetic field will become twice.