3 seater = 75 inch x 33 inch
2 seater = 53 inch x 33 inch (considering if 1+ 1 seat done from 2 seater) 
1 seater = 27 inch x 33 inch

For the first wash, it is recommended to hand wash the sofa cover in cold water separately. This helps prevent any potential color bleeding or damage. However, starting from the second wash onwards, you can use a washing machine.
If the sofa cover is made of pure cotton and you are concerned about color fading, there are a couple of options. First, you can soak it in cold water mixed with rock salt for a full night before washing it separately. This method can help fix the colors to some extent. Alternatively, you can use a color fixer specifically designed for fabrics. Apply it during the first wash, and from the second wash onwards, you can use a washing machine.
If the fabric of the sofa cover is Jacquard Handloom Cotton, it is recommended to wash it separately in cold water for the first wash.
Note: If needed, iron the fabric from the back side using a low temperature to avoid any damage or discoloration.

Please select the product as per the reference image i.e. 3+1+1 or 3+2