How big will my puppy get?

Why simple rules disagree

Puppies don’t gain weight at a steady pace. They grow fastest in the first few months, then slow down sharply as they approach adult size. Small dogs reach that slowdown early and large dogs late. In a study of 65 Toy Poodles, puppies reached half their adult weight at about 11 to 12 weeks (Menchetti et al. 2020). In a study of Labrador Retrievers, the fastest weekly gains came at about 13 weeks, and females reached mature weight at about 50 weeks (Trangerud et al. 2007).

Any rule that multiplies today’s weight by one fixed number assumes every puppy is at the same point on that curve. That is why two rules can give a 50 lb and a 100 lb answer for the same puppy, and why the size of the dog matters as much as the formula.

The ×52 rule

The most common rule online divides weight by age in weeks and multiplies by 52. It assumes the puppy keeps gaining the same amount every week for a year. Because growth slows down, the rule overestimates more the older the puppy gets.

The table compares the rule’s multiplier with the multipliers from the growth curves behind our puppy weight calculator. Each curve range runs from an early to a late maturing puppy of that size. To estimate adult weight, multiply today’s weight by the number.

Here is what that means for one puppy. A large-breed puppy weighing 22 lb at 12 weeks comes out at about 95 lb with the ×52 rule. The large-breed curves put it at about 60 to 69 lb. If the breed’s adults usually weigh 55 to 80 lb, as the AKC weight chart lists for Labrador Retrievers, the curve answer is the believable one.

Doubling the 16-week weight

Another rule you’ll see says to double the weight at 16 weeks. Against the curves, this works well for large breeds, whose multiplier at 16 weeks is about 1.9 to 2.2. It overestimates toy and small dogs, which are already 60 to 70% grown by then, and it can underestimate giant breeds, which still have a lot of growing to do.

A version that multiplies the 14-week weight by 2.5 behaves the same way. At 14 weeks the curves give about 1.6 to 1.8 for toy dogs, 1.9 to 2.3 for medium dogs, 2.2 to 2.5 for large dogs and 2.8 to 3.2 for giants. So the 2.5 figure fits a slow-maturing large puppy and overshoots most smaller ones.

What makes an estimate better

• Know the size class. A breed narrows the answer more than any formula; for a mixed breed, pick the size you expect from the parents.
• Weigh again later. Estimates before 12 weeks are wide; by 16 to 20 weeks the range is much tighter.
• Check body condition. A puppy that is too thin or carrying extra weight skews any projection. Aim for 4 or 5 on the 9-point WSAVA body condition chart.
• Use more than one weigh-in. The puppy growth chart shows whether your puppy keeps the same position on its curve over time.

If you know the parents’ adult weights, the calculator lets you enter them for reference. We don’t put them into the math, because we haven’t found published data on how well parent weight predicts a puppy’s adult size.