This is a more gentle way to stretch your calf and your achilles if a standing stretch is too painful, or you are non-weightbearing. To determine if a calf stretch may be appropriate for you, refer to this post https://ascentpt.wordpress.com/2014/05/12/exercise-of-the-week-half-kneel-dorsiflexion-stretch/.
Sitting in a long sit position with knees straight, loop a towel or sheet around the ball of the foot. Pulls towards you so you feel a stretch in the calf. Hold this for 30 seconds. Then, bend the knee and perform the same stretch.
If you are non-weightbearing, please check with your doctor or physical therapist first to make sure this is a safe stretch for you.