You can make use of [UIFont systemFontSize]
.
myLabel.attributedText = [[NSAttributedString alloc]
initWithString: @"my text"
attributes: @{
NSFontAttributeName: [UIFont italicSystemFontOfSize:
[UIFont systemFontSize]]}]];
Moreover, there are few more options to choose from:
+ (CGFloat)labelFontSize;//Returns the standard font size used for labels.
+ (CGFloat)buttonFontSize;//Returns the standard font size used for buttons.
+ (CGFloat)smallSystemFontSize;//Returns the size of the standard small system font.
+ (CGFloat)systemFontSize;//Returns the size of the standard system font.