Forty-five percent relative humidity is the comfortable relative humidity level. Below 30 percent humidity, the air feels dry, and above 52 percent relative humidity, the air feels very moist.
The relevant metric for measuring humidity is relative rather than absolute humidity. Relative humidity is the amount of water vapor in the air at a given temperature divided by the amount of water vapor the air can hold at a given temperature. Thus, at a relative humidity of 100 percent, the air is holding as much water vapor as it can. The air feels warmer at higher relative humidity because less sweat evaporates from the skin. At lower relative humidity, the air feels cooler because sweat evaporates more readily.