“That’s a rather personal question, Sir”. However, if you’re referring to an object in a photo, and not a line from a Monty Python sketch, here’s a useful tip. A foot-long piece of foam core with a printed checkerboard at 1”, 3” and 6” increments will be the answer to your scaling woes. 
Place the foam core stick next to the object you’re photographing, and when you get back to the office, you’ll know exactly how big the object it is. Note, scaling of “personal” objects is
not recommended.
