Iphone – How to calculate the size of a UIFont when text in label is constrained down to fit width

If you just want to have the label be as large as it needs to be to contain the label, you can set it to larger than it needs to be in any circumstance and align it as necessary.

Another option is this:

label.text = newText;
CGRect bounds = label.bounds;
bounds.size = [newText sizeWithFont:label.font];
label.bounds = bounds;

Since sizeWithFont is deprecated, I'm just going to update my original answer to using Swift 4 and .size

//: Playground - noun: a place where people can play

import UIKit

if let font = UIFont(name: "Helvetica", size: 24) {
   let fontAttributes = [NSAttributedStringKey.font: font]
   let myText = "Your Text Here"
   let size = (myText as NSString).size(withAttributes: fontAttributes)
}

The size should be the onscreen size of "Your Text Here" in points.