Hair volume is a matter of the number of hairs per square inch
Here's an easy way to determine the volume of your hair: Pull your hair back into a ponytail. If the base of the ponytail is very slim—about the diameter of a dime— the volume of your hair is thin. Another clue for thin volume: can you see your scalp when your hair is wet? If so, your hair is probably a thin hair volume type
If your ponytail is "two-fisted"—and looks almost like a true horse's tail—your hair a thick hair volume type. When your hair is wet, it covers your scalp very well, without any of the scalp showing through.
If you fall between these extremes, you have a medium hair volume type—this is the most common hair volume type.
Thick Hair Volume Type
Thick hair volume type is often very strong and you're likely to have hard to manage hair. A thick volume of hair may be overwhelming on someone with a slim frame and small face, particularly if the hair is also curly. The goal may be to reduce the volume of the hair, starting with the right haircut. A layered haircut can give thick hair more shape and direction, as well as reducing the thickness of the hair. Layered cuts in shorter and medium lengths are great for thick hair. Silkening hair care products—pomades, surfacers, and even strong hair gels can add control and manageability to thick hair. Very straight, thick hair is often resistant to perms, can be stubborn about holding a curl, and will most likely need frequent perming to maintain the thick hair's new texture.