How many paving brick are needed per sq metre?

Varies depending on the size of the bricks.

Paving blocks come in various sizes depending on the type of paving.
Standard paving blocks are are of pre cast concrete 100 mm by 200 mm the thickness varies. The heavier the traffic the thicker the blocks.
There are however, standard thickness's, 50 mm, 80 mm, and 100 mm are the most common.
For instance on a house driveway 50 mm blocks would be the most favoured, whilst on a dockyard which is used by heavy vehicles 100 mm blocks would be the choice.

You would need 50 standard blocks to cover one square metre.