Hello Everyone ! I'm currently reading a book about computer Architecture and i know that the number of die per wafer can be calculated as : dies per wafer = [PI*(waferdiameter/2)^2]/die area – (PI*waferdiameter)/sqrt(2*die area) .

I was reading this example : Find the number of dies per 300mm (30 cm) wafer for a die that is 1.5 cm on a side .

The answer say : The die is 2.25 cm^2 .Thus
Die per wafer = PI * (30/2)2 / 2.25   - (PI * 30) / Sqrt( 2* 2.25) = 270.

my problem is where did the 2.25 come from ? Please help ?

Area of rectangle is : Width x Height .

so, which means the 1.5 cm is only one side/ half  of the area ?