The length and texture of your hair are important factors as you determine what size perm rods to use for a perm. The type of curl you desire is another important factor that will help you narrow your selection down to the rods that will help create the curl you crave. Take the time to choose carefully to ensure that your perm is a healthy and attractive style for your hair.

Select red or blue perm rods if your hair is less than three inches long. Red rods are the smallest perm rods, suitable for the shortest hair and for creating the tightest curls. Blue rods are the next larger perm rods, suitable for hair between two and three inches long and for creating wavier curls in shorter hair.

Choose pink or gray perm rods if your hair is between three inches and five inches long. Pink rods are the smaller mid-size perm rods, suitable for making tight curls in medium-length hair or looser curls in short hair. Gray rods are slightly larger than pink rods, delivering similar results for slightly longer hair.

Use white or purple perm rods if your hair is at least 4 1/2 inches long. Purple perm rods are the largest rods, useful for creating waves in medium hair or curls in very long hair. White perm rods are slightly smaller than purple rods, suitable for adding body to short hair, waves to medium hair and curls to longer hair.

Combine perm rods for your hair if you have layers of different lengths. For example, use blue or pink rods if you have short layers in front. Use gray rods at the crown of your head and white or purple rods for your longest length.