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Puppy Weight Calculator

Get a rough idea of how big your puppy will grow, from its weight today, its age in weeks and its expected adult size. You also get a likely range.

Level: Grade 6

  • Common Core standard 6.RP.A.3.cFind a percent of a quantity as a rate per 100 (e.g., 30% of a quantity means 30/100 times the quantity); solve problems involving finding the whole, given a part and the percent.
Printable worksheet

Puppy Weight Calculator

Know the answer you need? Pick an input to work backward.

Inputs

From 8 weeks to 2 years. One month is about 4.35 weeks.

Use the breed's usual adult weight, or for a mixed breed, the parents' sizes if known.

Result

Estimated adult weight

32.3 lb

A 10 lb medium-size puppy at 12 weeks has reached about 31% of its adult weight, so it may grow to about 32.3 lb.

Likely range
27.4 to 37.1 lb
Share of adult weight reached
31%
Weight still to gain (about)
22.3 lb
Estimate in kg
14.6 kg

See the step-by-step solution ↓

Step-by-step solution

  1. Look up how much of its adult weight a medium dog has: 20% at 8 weeks and 31% at 12 weeks. Then read between them for 12 weeks

    0.2+12−812−8×0.31−0.2=0.31

  2. Today's weight is that share of the adult weight, so divide by the share to get the adult weight

    10 lb0.31=32.258065 lb

  3. Allow 15% either side, because individual puppies grow differently

    32.26×(1 ± 0.15)=27.4 to 37.1 lb

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Get a rough idea of how big your puppy will be as an adult. Puppies grow fastest in their first few months, then slow down as they near adult size. Small breeds race through it and are close to full grown before their first birthday. Giant breeds can keep filling out until they're about two. If you know roughly where your puppy is on that growth curve, its weight today hints at its adult weight. That helps when you choose a crate, a bed, a harness or a food plan.

Enter your puppy's current weight, its age in weeks and the size class you expect it to end up in. The calculator estimates the adult weight and gives a likely range around it. It also shows how much of its adult weight your puppy has probably reached already.

Where it's used

Why this math matters outside the classroom:

  • Choosing a crate. Owners of a 10 lb medium-breed puppy at 12 weeks plan for an adult of about 32 lb when buying a crate.
  • Percent problems. Students find the whole from a part and a percent: 10 lb is 31% of the adult weight, so 10 ÷ 0.31 ≈ 32.3 lb.
  • Shelter adoptions. Shelter staff give adopters a rough adult size for a mixed-breed puppy from its weight and age.
  • Budgeting for food. New owners estimate a large-breed puppy weighing 30 lb at 26 weeks may reach about 55 lb.

Grade level and standards: Grade 6; Common Core State Standards for Mathematics 6.RP.A.3.c. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Weigh your puppy and enter the weight in pounds or kilograms.
  2. Enter its age in weeks, from 8 weeks to 2 years. For months, multiply by about 4.35.
  3. Choose the expected adult size class from the breed, or for a mixed breed from the parents' sizes if you know them.
  4. Read the estimate and the range. If the estimate falls outside the class you chose, your puppy may belong in a different class.

What the inputs mean

Age in weeks
Use the age on the day you weighed your puppy. Estimates are least reliable for very young puppies, because their growth varies the most.
Expected adult size
Classes by usual adult weight: toy under about 12 lb (5 kg), small about 12–25 lb, medium about 25–50 lb, large about 50–90 lb and giant over about 90 lb (41 kg).

Formula and method

adult weight ≈ current weight ÷ share of adult weight reached at this age
share at age t = share at a + (t − a) ÷ (b − a) × (share at b − share at a)   (a ≤ t ≤ b in the growth table)
likely range = estimate × (1 − 0.15) to estimate × (1 + 0.15)

Say a puppy has reached 31% of its adult weight. Then its weight today is 31% of its adult weight. So dividing today's weight by 0.31 gives the estimate. Everything rests on that share.

The calculator uses a simple growth table for each size class. It lists the rough share of adult weight at 8, 12, 16, 20, 26, 39, 52, 65, 78 and 104 weeks. The curves are built around the age when each class usually finishes growing. That's about 9 to 10 months for toy dogs and about a year for small dogs. It's 12 to 15 months for medium dogs, 15 to 18 months for large dogs and 18 to 24 months for giant dogs.

For an age between two table rows, the calculator reads between them in a straight line. This is called interpolation. In the formula, t is your puppy's age, and a and b are the table ages just below and above it.

These curves are rules of thumb, not measurements for any breed. So the result comes with a range of 15% either side. The low end never goes below your puppy's current weight.

Worked example

A 12-week-old puppy of a medium-sized breed weighs 10 lb.

  1. At 12 weeks, the medium-size curve puts a puppy at about 31% of its adult weight.
  2. Adult weight ≈ 10 ÷ 0.31 = 32.3 lb.
  3. Range: 32.26 × 0.85 = 27.4 lb to 32.26 × 1.15 = 37.1 lb.
  4. It still has about 22.3 lb to gain.

Result: The puppy may grow to about 32.3 lb as an adult (about 14.6 kg), most likely somewhere between 27.4 and 37.1 lb.

Understanding the result

Use the estimate for planning, like what size crate or harness to buy. It isn't a target weight. Steady growth and good body condition matter more than matching any number.

Run the estimate again every few weeks. As your puppy gets older, it has reached more of its adult weight, so the estimate gets steadier.

Your vet can check body condition and tell you whether your puppy's growth looks right for its breed.

Assumptions and limitations

  • The puppy follows a typical growth curve for its size class.
  • The size class is chosen correctly. Mixed-breed puppies may follow either parent's pattern.
  • The growth table is a general rule of thumb, not data for a specific breed. Individual dogs vary widely.
  • It doesn't judge whether a puppy is underweight or overweight. Only a vet can assess that.
  • Ages below 8 weeks aren't accepted, because early growth varies too much for this method.

Frequently asked questions

At what age is a puppy half its adult weight?

In this calculator's model, it's around 16 weeks for small dogs and about 19 to 20 weeks for medium dogs. It's about 23 weeks for large dogs and close to 7 months for giant dogs. Toy breeds get there earliest, at about 13 to 14 weeks.

Can paw size predict how big my puppy will get?

Big paws often go with a big adult dog. But paw size on its own isn't a reliable guide. Weight at a known age, plus the breed or the parents' sizes, is a better one.

What size class should I pick for a mixed-breed puppy?

If you know the parents, use their average adult weight. If not, a guess from the shelter or your vet is a good start. You can run the estimate again later. If it keeps landing outside the class you chose, switch to the class it suggests.

When do puppies stop growing?

Small breeds usually finish growing by about a year, and medium breeds by 12 to 15 months. Large breeds finish by 15 to 18 months, and giant breeds by about 2 years. Many keep filling out a little after they stop getting taller.

How this calculator is checked

Method: Proportional estimate (adult = current weight ÷ share of adult weight) using the calculator's own rule-of-thumb growth table per size class, built around commonly quoted ages at which each class finishes growing. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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