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 data collected, ever
โ Everything stays on your device
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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100% On-Device
Nothing leaves your browser. Progress auto-saves to your own device using localStorage. Export a CSV or PDF anytime โ reimport later to resume. No servers involved.
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Cited Sources
Every breed's growth curve is sourced from AKC standards and published veterinary studies โ not guesswork.
๐ The Story Behind PawSizer
It started with Ace.
In early 2026, a German Shepherd/English Shepherd mix named Ace came home from a shelter with a birthday that was anyone's best guess. His owner wanted to know: was December 9th right, or just a ballpark?
By logging his teeth, weekly weigh-ins, and a DNA breakdown (55% GSD ยท 26% English Shepherd ยท 19% Supermutt), the tool converged on a date within a week of the shelter's estimate. Not bad for a dog who arrived without paperwork.
PawSizer grew from that curiosity. Maybe you're tracking how fast your puppy is growing. Maybe you adopted a dog of unknown age. Maybe you just want a better answer than "probably about two years old." Either way โ 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. No tracking. Just open it and go.
Returning user? to pick up where you left off.
About PawSizer
How it works and why we 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 within 0.5 log-units of the peak; 95% CI within 2.0. 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
226 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.