how do I calculate how many bricks?

20m x 3m = 60 sq m

You say 60 bricks per square metre so you need 60 x 60 = 3600 bricks

This assumes your wall is 1 brick thick. If it's double thickness then you need 7200

Also, you should allow for some breakages and half bricks (if you need them)

Bricks Per M2

If 1 sqm =60 brick is considered correct then total brick will be 60x60=3600 brick.

Standard size means as per IS modular one brick (19x9x9 c.m.) & width mortar (20x10x10 c.m.) =0.20x 0.1=0.02 m2. For half brick thick, brick work measurement is in square meter therefore for one modular brick work area is 0.02 m2 therefore 1sqm = 50 brick ,wastage vary with quality of brick.

Non modular brick is 225 mmx111mmx70 mm (dimension is including mortar) For this 1 sqm brick= 1/(0.225x0.111)=40 brick (without wastage).

Good quality brick has wastage 5 to 10% The wastage is mainly in transportation, loading, unloading.Few bricks are broken or some of broken bricks are used for breaking joints.

For modular brick of thickness one brick ( that is 200 mm) then 1cum brick work it will be 500 brick.one sqm of one brick thick wall will contain=500*0.2=100 brick.

For non modular brick 1 ***=1/(0.225x0.111x0.07)=572 brick,For 1sqm of one brick thick it will be= 572x0.225= 128 brick.

This information is as per Indian Construction Practises (CPWD)

V = w*l*h Cross sectional area = Acs = w*l V = Acs*h a) V = 750 mm^2 * 8 mm V = 6000 mm^3 = 6000 cubic mm b) 1 cm = 10 mm (1 cm)^3 = (10 mm)^3 1 cm^3 = 1000 mm^3 V = 6000 mm^3 * (1 cm^3 / 1000 mm^3) V = 6 cm^3

how many bricks, sand, in 1 sqm ?

you can't figure this out without knowing how wide it is going to be. A= length x width , not length x height

difficult matter. look into the search engines. it can assist!