How old is your dog, really? How big will they get? Built for curious owners, shelter volunteers, and anyone who loves a good dog mystery.
โ Always free
โ No account needed
โ No ads
โ PUBLIC BETA ยท Algorithm under active validation. Results are estimates only.
How it works
Teeth, weight, height โ combined into one honest estimate.
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Puppies are the sweet spot (0โ7 months)
Erupting teeth and weekly weigh-ins give surprisingly precise estimates. The older the dog, the wider the range โ but even for adults, dental wear patterns can narrow things down to a year or two.
Tip: regular measurements tell a better story than a single snapshot.
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Dental Staging
The highest-confidence metric. Tooth eruption and wear follow precise timelines. Log individual teeth observations with dates for maximum accuracy.
โญ Highest weight
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Growth Curve Fitting
Plot weight and height measurements over time. We overlay your data on breed-specific reference charts sourced from veterinary literature.
๐ Trend-based
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Breed-Adjusted Modeling
Mixed-breed dogs get weighted averages of each parent breed's growth model. Supports unlimited breed combinations with custom percentage sliders.
๐ Multi-breed
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Alteration Adjustment
Early spay/neuter can affect how tall a dog grows. We account for this when projecting adult size.
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Cited Sources
Every breed's growth curve is sourced from AKC standards and published veterinary studies โ not guesswork.
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Save and Resume
Your progress autosaves on your device while you work, and you can export the full record as CSV or PDF and re-import it later from any browser.
๐ The Story Behind PawSizer
It started with Ace.
Ace came home from a shelter in early 2026 with an unknown history and a guessed birthday. I kept wondering how close that date really was, and whether his growth pattern could tell a clearer story.
So I started logging what I could: teeth, weights, height, and breed mix. The estimate got sharper with every entry and landed close to the shelter's best guess.
That's how PawSizer started: pure curiosity. You can use it for age estimates, size projections, or just to explore your dog's growth data in one place. No account, no ads, no catch.
Give it a try
Takes about 5 minutes. Works with whatever data you have โ even a single weight measurement helps.
No sign-up. No email. Just open it and go.
Returning user? to pick up where you left off.
About PawSizer
How it works and why I built it.
Methodology
How the estimate is calculated
PawSizer works by testing hundreds of candidate birth dates and scoring each one against your observations โ dental stage, growth measurements, and any known date. Whichever date best fits everything you've entered wins. The more observations you add, the narrower the answer gets.
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Dental staging โ highest priority
Puppy teeth follow a remarkably predictable schedule. Logging what you see โ and when โ is the single most useful thing you can do for a young dog. Becomes less useful after 18 months as eruption finishes and wear patterns take over.
Highest
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Growth curve fitting โ medium priority
A single weight reading doesn't tell us much. But a series of measurements over weeks shows a growth curve โ and that curve has a shape that points to a specific age window. Stops being useful once the dog is fully grown (~18 months).
Medium
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Known/shelter birthdate โ weak prior
Shelter estimates and breeder records are useful starting points. If the other evidence points somewhere different, the tool will say so โ but it won't ignore what you already know.
Prior
Worth knowing: PawSizer works best when you have measurements from puppyhood โ even years later, a growth trajectory recorded during a dog's first year is highly age-diagnostic. For adults with no puppy history, dental wear can give a broad range, though individual variation means a vet exam will always be more precise.
Our Custom Algorithm
How PawSizer goes beyond off-the-shelf statistics
Standard MLE finds the most probable date given the data. PawSizer adds four layers on top of that:
BCS correction
Each weight is adjusted for body condition (WSAVA 1โ9 scale) before fitting. An underweight dog at BCS 3 has their weight divided by 0.90 to estimate lean mass โ removing the confound of over or underweight dogs appearing older or younger than they are.
Breed envelope constraint
After MLE finds its peak, all BCS-corrected weights are checked against a biological range built from the breed mix โ lower bound from the smallest breed's minimum standard, upper bound from the largest breed's maximum. If any points fall outside, the estimate shifts to the earliest dental-consistent date where everything fits.
Shape fitting, not magnitude
Growth curve fitting uses scale-normalised shape matching. The algorithm finds the optimal size scale factor separately, then scores only the trajectory shape. A dog consistently 20% lighter than average isn't penalised โ what matters is whether their growth rate matches the curve at the implied age.
Peak-width confidence intervals
CIs come from the sharpness of the likelihood peak, not signal variance. The 68% CI spans dates whose joint log-likelihood is within 2.0 of the peak; the 95% CI within 8.0. Both thresholds inflate adaptively when residuals at the peak exceed the measurement-noise sigma, so poorly-fit samples report wider intervals. A sharper peak means more certainty โ more data, or data that points more clearly to one date.
Data Sources
Algorithm and dental staging references
Breed Growth References
235 breeds โ AKC, FCI, and breed club standards
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Limitations & Disclaimer
PawSizer is a curiosity tool, not a veterinary diagnosis. Estimates are best guesses based on the data you enter โ individual dogs vary, and nothing here replaces a conversation with your vet.
Export your own data (CSV / PDF) for your own records
โ You may not
Copy or redistribute the source code
Use the algorithm or data in another product
Reverse-engineer or create derivative works
Host or deploy PawSizer on another domain
Use PawSizer's name or branding elsewhere
No warranty. PawSizer is provided as-is for informational purposes only. Estimates are not veterinary advice. The author accepts no liability for decisions made on the basis of these estimates.