Project how big your puppy will get, using growth curves that differ by size class — because a Chihuahua and a Great Dane are nowhere near the same fraction of adult weight at twelve weeks.
Last reviewed July 2026 · Free · Nothing you enter is stored
The rules of thumb that circulate — double the weight at four months, multiply the 14-week weight by two and a half — are all attempts to compress a size-dependent curve into a single number. They work for whichever size class the person who coined them happened to own.
The real difference is substantial. A toy breed has reached about 62% of its adult weight by 16 weeks. A giant breed at the same age is at 34%. Apply the toy multiplier to a Great Dane puppy and you will underestimate its adult weight by nearly half. The underlying reason is that small dogs finish quickly and large dogs keep going: a Chihuahua is done growing before its first birthday, while a Mastiff is still adding mass at eighteen months.
This is the table the calculator interpolates between. Find your puppy's size class and age to see roughly where it should be:
| Size class | 8 wk | 12 wk | 16 wk | 20 wk | 24 wk | 36 wk | 52 wk |
|---|---|---|---|---|---|---|---|
| Toy under 12 lbs | 25% | 45% | 62% | 75% | 87% | 98% | 100% |
| Small 12–20 lbs | 22% | 40% | 55% | 68% | 80% | 95% | 100% |
| Medium 20–50 lbs | 18% | 33% | 47% | 58% | 68% | 87% | 97% |
| Large 50–90 lbs | 15% | 28% | 40% | 50% | 60% | 80% | 93% |
| Giant 90+ lbs | 12% | 24% | 34% | 43% | 52% | 72% | 87% |
Growth percentages follow published canine growth curves (Hawthorne et al., Journal of Nutrition 2004, and the Waltham puppy growth charts) generalised to five size classes. Individual puppies deviate by 10–15%, and mixed breeds are the least predictable of all.
Growth is not linear and it is not supposed to be. Puppies grow fastest in the first sixteen weeks, then the rate tapers. On a chart of weight against age the line rises steeply and then bends toward horizontal — an S-curve. This is why a puppy that seems to be exploding in size at ten weeks is not on track to become enormous; it is simply in the steep part of a curve that everything flattens out of.
What is worth watching is the shape rather than any single point. A puppy tracking steadily along its curve is doing fine even if it sits at the low end of the breed standard. A puppy that plateaus for a fortnight, or that jumps sharply after a food change, is telling you something — usually about parasites, illness, or a portion size that has drifted. Weighing weekly and writing the number down is a five-second habit that catches problems earlier than almost anything else you can do at home.
| Size class | Full height | Full weight | What is still happening |
|---|---|---|---|
| Toy | ~8 months | ~9 months | Essentially finished. Watch for the opposite problem — toy breeds gain weight easily as adults. |
| Small | ~9 months | ~11 months | Minor filling out in the chest through the first year. |
| Medium | ~11 months | ~14 months | Height finishes well before the frame does. |
| Large | ~12 months | ~18 months | Six months of broadening after the dog stops getting taller. Owners often think their dog is overweight during this phase when it is simply maturing. |
| Giant | ~14 months | ~24 months | The longest runway, and the one where growth rate matters most for joint health. |
For large and giant breeds especially, the evidence points the other way. Rapid growth driven by free-feeding or an over-rich diet is associated with hip dysplasia, elbow dysplasia, and osteochondrosis — the skeleton loads faster than it can remodel. Excess dietary calcium compounds it, which is why large-breed puppy foods control calcium rather than maximising it.
The target is a puppy that stays lean through growth and arrives at its adult size on schedule rather than early. The same Purina lifespan study that found lean adult dogs live about 1.8 years longer started its intervention in puppyhood. Our dog food calculator applies the puppy energy multipliers directly, and if you want the other end of the arc, the dog age calculator shows how size class governs the rest of a dog's life too.
For a purebred puppy of known size class weighed at 16 weeks or later, projections are usually within 10 to 15% of the eventual adult weight. Before 12 weeks the error is much larger, because early weight reflects litter size, birth order, and how well the puppy competed at the teat more than it reflects adult genetics. For a mixed breed with unknown parents, treat any single projection as a rough bracket and re-run it every month — the trend across several weighings is far more informative than one number.
It depends almost entirely on size class, which is the reason this calculator asks. A toy breed hits half its adult weight around 14 weeks; a medium breed around 17; a giant breed not until about 23. That spread is why a single rule of thumb — 'double the weight at four months' — works for some dogs and is badly wrong for others.
Toy and small breeds finish around 9 to 12 months. Medium breeds take 12 to 15. Large breeds reach full height near 12 months but keep filling out in the chest and shoulders until about 18. Giant breeds are the outliers: they can keep adding mass until two years, sometimes a little beyond. Height finishes first in every case — the growth plates close before the frame finishes broadening.
Less reliably, but the growth curve still applies once you can place the puppy in a size class. The usual approach is to estimate the size class from paw size, current growth rate, and whatever is known about the parents, then re-run the projection monthly as the trajectory clarifies. A DNA test that reports predicted adult weight is more accurate than any curve if the exact number matters to you.
Not necessarily, and the distinction that matters is frame versus fat. A large-framed individual, a mixed lineage, or a line bred for size will all read high and are fine. A puppy carrying excess body condition also reads high and is not — overfeeding during growth is associated with developmental orthopaedic disease in large breeds, and it is one of the few things about growth an owner directly controls. Ask your vet for a body condition score at the next visit; you should feel the ribs easily under a thin fat layer without seeing them.
Yes. Large and giant breed puppies need a food formulated for them, with controlled calcium and a lower energy density. Growing too fast is a documented risk factor for hip dysplasia and osteochondrosis, and excess dietary calcium interferes with normal skeletal development. The goal is a steady curve, not the fastest one — our dog food calculator sets the portion.
