Area of black hole in Planck units

(* units *)
units=
{
(* speed of light c in m/s (exact) *)
c->299792458,
(* Planck's constant in J s (exact) *)
h->6.62607015 (10^(-34)),
(* Newton's G in (m^3)(kg^(-1))(s^(-2)) *)
G->6.67384 (10^(-11)),
ℏ->(h/(2π)),
(* solar mass in kg *)
Msun->1.9891 (10^30)
}

(* Planck length in m *)
PlanckLength=(Sqrt[((G ℏ)/(c^3))])//.units

(* Schwarzschild radius of black hole mass M *)
rs=((2G M)/(c^2))

(* horizon area of black hole *)
A=4π (rs^2)/4/.M->4 (10^6)Msun//.units

(* entropy = area/4 in Planck units, for (SuperStar[SgrA]) black hole*)
(A/(4(PlanckLength^2)))/.M->4 (10^6)Msun//.units