What the number means
A puppy's weight at one age doesn't pin down its adult weight. Two Labrador puppies can both weigh 14 lb at 12 weeks and finish ten pounds apart. So this calculator doesn't hand you one figure and hope. It gives you a middle estimate and the range around it.
The range is an 80% range. On puppies the calculator had never seen, a little over four in five (84% to 87%, depending on age) ended up inside the range it would have given them. The rest finished above or below it. If you see a wide range, that isn't the tool being vague. That's how much puppies really vary at that age.
How it works
Dogs grow along a recognisable curve: fast at first, then slower, then flat. How quickly a puppy gets through that curve depends mostly on adult size. A toy dog has done about three quarters of its growing by 6 months. A large dog has done about two thirds. We measured those curves for six size classes, using the size categories from Salt et al. (2017) and the dataset behind that paper.
The calculator asks what share of its adult weight a typical puppy of your size has reached at your puppy's age, then divides your puppy's weight by it. If you pick a breed, the breed's typical adult weight acts as a second opinion and pulls the estimate toward it. If you leave the breed blank, the calculator works out which size class fits your puppy's own numbers.
For the full method, including how well it did on dogs it hadn't seen, read the methods page.
When the answer is most reliable
Later is better. In the data, a single weigh-in at 8 to 11 weeks was off by a median of about 18%. By 16 to 25 weeks that fell to about 12%, and at 39 to 52 weeks to about 6%. If your puppy is 9 weeks old and the range looks wide, check again at 16 weeks and again at 6 months.
Adding weigh-ins helps in a way a single reading can't. Puppies stay close to their own trajectory, so three weigh-ins at 8, 12 and 16 weeks say more than one at 16 weeks. The puppy growth calculator takes several readings at once, and a free account saves them.
Getting a weight you can trust
- Weigh at the same time of day, ideally before a meal. A full belly can add a few percent to a small puppy.
- Use one scale every time. A kitchen scale works for toy breeds. For bigger puppies, weigh yourself holding the puppy and then alone, and subtract.
- Write it down the day you weigh. Memory rounds in flattering directions.
- Don't use a weight from a day the puppy was unwell, or the first day after a vet visit with a big meal and a lot of excitement.
Mixed breeds and unknown parents
Leave the breed on 'mixed or unknown'. The calculator will still work, just with a wider range at young ages, because it has no outside clue about adult size. The first thing that helps is another weigh-in two to four weeks later. The second is knowing either parent's weight, which you can enter in the dog size calculator.
What this can't do
It can't see body condition. A puppy who is too thin or too round will skew the forecast, and the forecast shouldn't be used to decide how much to feed on its own. It also can't spot illness. If your puppy stops gaining, loses weight, or is much lighter than littermates, that's a vet question, not a calculator one. Giant breeds over 40 kg (88 lb) are included, but the paper behind our size classes didn't produce charts for them because breeds like the Great Dane and the Mastiff grow so differently. Treat those forecasts as looser.
How to use it, step by step
- Weigh your puppy. Use the same scale each time, before a meal. For larger puppies weigh yourself holding the puppy, then alone, and subtract.
- Enter age and weight. Type the puppy's age in weeks or months and the weight in pounds or kilograms.
- Pick a breed if you know it. A breed gives the forecast a second source of information and narrows the range, especially under 16 weeks.
- Read the range, not just the middle. The likely adult weight is the middle. About 4 in 5 puppies end up inside the 80% range.
- Weigh again in 2 to 4 weeks. More weigh-ins tighten the range. Save them in a free account so the forecast updates.
Questions people ask
How accurate is a puppy weight calculator?
It depends on age. In our test on puppies the calculator hadn't seen, a single weigh-in at 8 to 11 weeks was off by a median of about 18%, at 16 to 25 weeks by about 12%, and at 39 to 52 weeks by about 6%. The 80% range is there to show the real uncertainty.
At what age can you predict a puppy's adult weight?
The data starts at 8 weeks. Predictions are usable from there but get much tighter from about 16 weeks, and are quite good by 6 months.
Does the sex of the puppy matter?
Males run a little heavier than females in most breeds, but within one size class the shape of the growth curve is similar. This calculator doesn't split by sex. Entering a breed's typical weight accounts for most of it.
Is the 'double the weight at 14 weeks' rule true?
It's a rough rule that fits some medium dogs and misses badly for others. In our data a medium dog is typically at about 34% of adult weight at 14 weeks, so doubling gives about 68% of adult, not 100%. A large dog is even further off.
What if my puppy is much bigger or smaller than the forecast says later?
Most puppies stay on their own curve, but some drift. Weigh again, keep the log, and ask your vet if your puppy falls well away from the forecast or stops gaining.
Is this calculator storing my puppy's weight?
No. Nothing you type in the calculator is saved. Create a free account if you want to keep weigh-ins and see the forecast update.
Last reviewed October 31, 2026. General information, not veterinary advice. Growth curves are PupCurve's analysis of data from Salt et al. 2017 (CC BY 4.0). How it works.