This is ONLY A ROUGH GUIDE!!! Puppies like people have varying grow spurts, some are smaller when they are young and grow larger later, the reverse is also true. Eating or fasting right before weighing can also alter the results. Don't obsess over your puppy's weight, and defiantly don't try and make your puppy stay smaller by limiting food. They will become malnourished but grow anyway.
To use this chart first weight your puppy and convert pounds to ounces if necessary remember 1 pound =16 ounces. Then find the age of your puppy on the left. Follow the line along horizontally until you find your puppy's current weight next follow that line vertically to the bottom of the chart where an approximate adult weight is given. For example; a 10 week old puppy current weighs 2.2 lbs (conversion 16 X 2 + 2 = 34 ounces), it is estimated to be 5.5 pounds as an adult
When in doubt another general rule is 3 times the weight at 8 weeks old or 2 times the weight at 12 weeks.