Hey Vijay Kumar Verma,

The quantity of cement and sand according to various ratios is given below.
1. 12 mm cement plaster 1:6 = Cement 0.074 Bag per sq .meter
Sand 0.018 CUM per Sq. Meter
2. 12MM cement plaster 1:4 = Cement 0.11 Bag. Per Sq. Meter
Sand 0.017 CUM per Sq. Meter
3. 12 MM cement plaster 1:3 = Cement 0.15 Bag. Per Sq. Meter
Sand 0.165 cum per Sq. Meter
However if you want to calculate the quantity of material, the basic formula is given below for the area 10 X 12 feet and thickness 3/8 inch( 10 MM). The quantity of material comes out = 10 X 12 X3/8 X1/12 = 3.75 CFT. This is the volume of wet mortar.
Quantity of Dry mortar is 1.2 times of the wet mortar. So cement sand quantity = 3.75 X1.2 =4.5 CFT.    
Now ratio given is 1.3 quantity of the cement comes out =4.5 X1/4=1.125 CFT or one bag. Quantity of sand = 4.5x3/4=3.4 CFT.

Thanks