Someone who isn't at all upset, agitated, or anxious has the quality of calmness. Even though you're a nervous flier, your seatmate's calmness will help reassure and soothe you during your long flight.
Your famously patient and composed grandfather is well known for his calmness, and your boss may compliment your own calmness under pressure if you're never rattled during busy shifts at work. Places and situations can also have this quality: "The calmness in my friend's quiet house is a contrast to my huge, noisy family." A lack of intense weather is another kind of calmness, like the calmness on a lake after a storm passes.