### How many Blocks do i need to build a extension 3.5Mx3.5M x ...

Jan 05, 2009· Hi standard blocks are 450mm x 225mm high so its 10 to a square mtr. so i expect your extention has 3 side so 3.5 trs x 2.4 mtrs = 8.4 mtrs x 10 blocks = 84 blocks x 3 walls = 252 blocks skin x 2 = total 502 blocks. and then you need to take away the area of your windows and door.