Puppy Weight Calculator
Estimate your puppy's adult weight.
An estimate for a typical dog, not a promise. Your vet knows your pet.
How to use the puppy weight calculator
- Enter weight now. The rule multiplies this number. A guess becomes a wrong adult.
- Enter age in weeks. Toy and small rules are stated for 8 weeks. Medium, large and giant rules are stated for 16 weeks.
- Pick a size class. The note under the list is the maturity window Merck gives for that class, plus which rule the class uses.
- Read predicted adult weight and the low and high ends. The band is wide on purpose.
- If the age is not the rule's week, the warning says the math is pretending today's weight is the weight at that week. Weigh again then.
Two rules of thumb, and nothing finer
The boxes open with a labelled example: 3 times the weight at 8 weeks for toy and small, and 2 times the weight at 16 weeks for medium, large and giant. Replace the idea if a clinic gave you another figure. Toy is grouped with the small example. Giant is grouped with the medium-and-large example. That grouping is part of the example, not a breed-club standard.
The page opens on a medium puppy at 12 weighing 15 lb. The medium example wants 16 weeks, so the adult line, 30 lb, is what you would get if 15 lb were the 16-week weight, with a low of 25.5 lb and a high of 34.5 lb. The percent, 50 %, belongs at 16 weeks, not at 12 weeks.
There is no month-by-month table. Merck's feeding chapter says only limited breed-curve data have been published, and that a chart can be plotted for an individual puppy. This page shows the labelled example with a wide band. It is not that chart.
What Merck does say about timing
Puppies gain quickly for about the first 5 months. In that stretch Merck describes an average gain of 2–4 g per day per kilogram of the adult weight you expect. That sentence needs the adult weight you are trying to find, so it is not used backwards to invent one.
Skeletal maturity is a different sentence, and it is cited. Small and medium breeds often finish between 8 and 12 months. Large and giant breeds often finish between 10 and 16 months. The size list shows the window that matches the class. The opening class starts that window at 8 months.
A slow gain is preferred to a fast one. The feeding chapter is blunt that pushing growth fights sound bone. If the adult estimate is being used to justify a huge bowl, stop and use the puppy feeding page, which follows the calorie factor instead of a size dream.
How to read a number that is only rough
Say it as a range. '30 lb, likely 25.5 lb to 34.5 lb, if the rule applies' is the honest form. Dropping the range makes a habit look like a measurement.
Weigh at the reference week if you can: 8 weeks for toy and small, 16 weeks for the others. An estimate taken at 12 weeks for a medium puppy is the opening example of the wrong week. The warning under the result says the figure treats today's weight as the weight at the rule's age.
This page does not list official adult weights by breed. The class list is five labels: toy, small, medium, large and giant.
Rules of thumb, not a growth curve
| Class | Rule | Adult if 15 lb were the reference weight | Percent at the rule's age |
|---|---|---|---|
| Toy | 3 × at 8 weeks | 45 lb | 33 % |
| Small | 3 × at 8 weeks | 45 lb | 33 % |
| Medium | 2 × at 16 weeks | 30 lb | 50 % |
| Large | 2 × at 16 weeks | 30 lb | 50 % |
| Giant | 2 × at 16 weeks | 30 lb | 50 % |
Labelled examples only. Toy and small open at 3 × weight at 8 weeks. Medium, large and giant open at 2 × weight at 16 weeks. Replace them. The band is wide. There is no month-by-month curve.
Tips and common mistakes
- Do not average this adult weight with a breed guess you found elsewhere and treat the blend as more accurate.
- The wide band is ±15% around the rule. It is a caution, not a statistical confidence interval from a paper.
- Giant puppies are not 'late small dogs'. They use the 16-week rule and a longer maturity window.
When to call your vet
- The puppy is not gaining from week to week.
- Legs look bowed or the puppy is sore, especially in a large breed that is growing fast.
- You need to know whether a particular breed's adult range is healthy for this puppy. This page cannot say.
- The estimate is being used to decide a surgery, a diet cut or a sale price.
Frequently asked questions
How accurate is a puppy weight prediction?
Not very. The opening medium puppy produces 30 lb only by treating today's weight as a 16-week weight, inside 25.5 lb to 34.5 lb. It is a habit with a wide band, not a promise.
When do puppies stop growing?
Merck: skeletal maturity is often 8–12 months in small and medium breeds and 10–16 months in large and giant breeds. The class you picked shows its window under the list. Obvious height can stop before the skeleton is finished.
Is my puppy too small or too big?
This page will not score that. It has no curve that says what percent of adult weight a 12-week medium puppy should have reached. Weigh again at the rule's week, and ask the clinic if gain has stalled.
Why is there no month-by-month chart?
The table on this page is only the two rules of thumb, applied to one example weight. It is not a month-by-month growth curve.
Which rule does a medium puppy use?
The 2× rule at 16 weeks. The multiplier on screen is 2 and the reference age is 16 weeks. At 12 weeks you are four weeks early for that rule.