dynamic_label_height.swift

extension UILabel{
    func dynamicHeight() -> CGFloat {
        let label = UILabel(frame: self.bounds)
        label.numberOfLines = self.numberOfLines
        label.lineBreakMode = self.lineBreakMode
        label.font = self.font
        label.text = self.text
        label.sizeToFit()
        return label.frame.size.height
    }
}

usage_of_dynamic_label_height.swift

let myLable = UILabel(frame: CGRect(x: 10, y: 20, width: 100, height: 20))
myLable.text = "Implements a read-only text view. A label can contain an arbitrary amount of text, but UILabel may shrink, wrap, or truncate the text, depending on the size of the bounding rectangle and properties you set. You can control the font, text color, alignment, highlighting, and shadowing of the text in the label."
myLable.numberOfLines = 0
let expectedHeight = myLable.dynamicHeight()
myLable.frame = CGRect(x: 10, y: 20, width: 100, height: expectedHeight)