Age: 16 months
Weight: 66 pounds (exactly. Weight taken at the vet.)
Length: about 31 inches
Shoulder height: about 15 inches

Age: 8 1/2 months
Weight: 48 pounds (exactly. Weight taken at the vet.)
Length:  Approximately 22 inches
Shoulder height:  Approximately 14 inches

Age: 5 months, 3 weeks
Weight: Approximately 22 pounds (estimated)

Age:15 weeks
Length:  17 inches
Shoulder height: 6 inches
Weight:  18 pounds

What's your pig's weight?  Here's a way to guestimate it:
1) Measure the girth (the area just behind the front legs).
2) Multiply this measurement by itself.
3) Then multiply that figure by the length of your pig (ears to beginning of tail).
4) Divide by 400 and you will have the approximate weight of your pig.
Taken from a post to the PetPigs e-mail list.