VariableCellSize.m

@interface MyCell : UITableViewCell
+(CGSize)cellSizeForText:(NSString*)text;
@end



#import "UIView+NFCore.h" // "instantiateFromNib:"

@implementation MyCell

static CGSize const kCellMargins = (CGSize) { .width = 20, .height = 20 };

+(CGSize)cellSizeForText:(NSString*)text
{
  static CGSize cellSizeXIB;
  static CGFloat labelSizeXIB;
  static UIFont* labelFontXIB;

  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    UINib *cellNib = [UINib nibWithNibName:NSStringFromClass([self class]) bundle:nil];
    MyCell *dummyCell = [self instantiateFromNib:cellNib];
    cellSizeXIB = dummyCell.bounds.size;
    labelSizeXIB = dummyCell.mylabel.frame.size;
  });

  CGSize labelSize = [text sizeWithFont:labelFontXIB constrainedToSize:labelSizeXIB.width];
  
  // Keep the margins between the label and the cell from the XIB, adjust only height
  return CGSizeMake(cellSizeXIB.width , cellSizeXIB.height + (labelSize.height - labelSizeXIB.height));
}
@end