How to get the height of a UILabel in Swift?

Swift 4 with extension

extension UILabel{

public var requiredHeight: CGFloat {
    let label = UILabel(frame: CGRect(x: 0, y: 0, width: frame.width, height: CGFloat.greatestFiniteMagnitude))
    label.numberOfLines = 0
    label.lineBreakMode = NSLineBreakMode.byWordWrapping
    label.font = font
    label.text = text
    label.attributedText = attributedText
    label.sizeToFit()
    return label.frame.height
  }
}

it's simple, just call

label.bounds.size.height