Bathtubs come in a variety of sizes and shapes ranging from compact ones for a single person to capacious Jacuzzis for the whole family. Decide on whether you want the appliqués to cover the entire bathtub surface or just the parts that you step on when you enter and exit the tub.
Bathtub appliques usually come in sets of 6, 10 or more. Check the dimensions of each applique to know whether one set will give you the coverage that you seek. You will need multiple sets to cover large tubs.
Alternatively, you can opt for bathtub mats. These are as big as a bath towel and can suffice for a standard sized tub.