what is the paper size A4 in Sq Cm ?

A 4 paper size is 21cm x 29.7cm = 623.7 cm^2

A series paper sizes are defined as follows; the A0 size has an area of one square metre, and each successive size is half the one previous. Also, if an A series sized piece of paper is cut or folded on half along its width, then the piece of paper formed is the same shape as the piece you started with; this means that the paper has length and width in the golden ratio, 1.618034... to 1.

A4 paper is therefore formed by 4 successive halvings, so it has an area of one sixteenth of a square metre or 625 cm2.

21cm x 29.7 cm=623.7cm

http://www.cl.cam.ac.uk/~mgk25/iso-paper.html

A4 Sizes In Cm

A3 420 x 297 mm (42 x 29.7cm) A4 297 x 210 mm (29.7 x 21cm) A5 210 x 148 mm (21 x 14.8cm)

210mm * 297mm * 0.01mm²/cm² = 623.7cm²