How to calculate spacing of reinforcement bars as per the area of steel?

In this post the answer to the question given above which is faced by almost all civil engineers during their starting days at site is given below.
If you have to calculate the centre to centre spacing of bars as per the given area of the steel for a certain dia of bar you can follow the below stated procedure;

Area of Steel 'Ast req.'              = 1536 sq mm
Dia of Bar to be provided 'd'   = 16 mm (round bar)
Area of cross-section of 1 bar = 0.785 x d^2 = 0.785 x 16^2 = 200.96 sq mm
Spacing required                     = Area of 1 bar x 1000 / (Ast req.) = 200.96 x 1000 / 1536 = 130.83 mm

Hence, in the above given example spacing for 16 mm dia bar has been calculated, thus if 16 mm dia bars at 130 mm c/c are provided then the steel area provided is 1545.84 sq mm.

Now one more thing with just a little change in the formula same formula can be used for determining the Ast provided for the given Spacing;

Dia of bar                    = 16 mm
Spacing of bar c/c       = 125 mm
Area of cross section  = 200.96 sq mm
Ast provided               = Area of Cross-section  x 1000 / spacing = 200.96 x 1000 / 125 = 1607.68 sq mm

Thus provision of 16 mm dia bars at 125 mm c/c is provided then the area of steel provided in the region is 1607.68 sq mm.