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How Big Will My Chihuahua Puppy Get? Why Charts Fail, and What the Size Genes Tell Us
Updated: 7 days ago
By Rev. T. Stringer, Lead Researcher, SIPGS
"How big will this puppy be?"
It is the question breeders hear most.
Many people now expect a DNA test to answer it.
DNA will get there.
Right now, we are still learning how the size genes work in Chihuahuas.
The breed standard
The AKC standard says a Chihuahua should not exceed 6 pounds.
Over 6 pounds is a disqualification in the show ring.
There is no minimum weight in the standard.
The five size genes on an Embark report
Embark reports five body-size markers.
All five come from a 2013 study of size genes across many dog breeds.
Marker | Smaller result | Larger result |
IGF1 | II | NN |
IGF1R (Embark prints "IGFR1") | AA | GG |
STC2 | AA | TT |
GHR E191K | AA | GG |
GHR P177L | TT | CC |
In a mixed group of breeds, these markers help explain why a Chihuahua is smaller than a Great Dane.
That is a very different question from why one Chihuahua is 4 pounds and another is 7.
What SIPGS found
We collected the Embark size results for:
238 Chihuahuas
106 came from original Embark reports, all 100% Chihuahua.
132 came from public Embark profiles of dogs that SIPGS DNA checks place with Chihuahuas.
Marker | Smaller | Middle | Larger |
IGF1 | 238 (100%) | 0 | 0 |
GHR E191K | 234 (98%) | 2 | 2 |
STC2 | 218 (92%) | 19 (8%) | 1 |
IGF1R | 6 (3%) | 63 (26%) | 169 (71%) |
GHR P177L | 159 (67%) | 65 (27%) | 14 (6%) |
IGF1 never changes. Every Chihuahua we tested has the small version.
GHR E191K and STC2 almost never change.
On their own, these three do not tell one Chihuahua from another.
Only IGF1R and GHR P177L really vary.
And look at IGF1R.
71% of Chihuahuas carry the "larger" GG.
Only 3% carry the "smaller" AA.
Yet most Chihuahuas are well under 6 pounds.
In this breed, "GG, larger" is the normal result, not a warning sign.
Same genes, different sizes
We then compared the markers with real, measured adult weights.
Not Embark's predicted weight. A dog on a scale.
17 of our adults had both a verified Embark report and a scale weight.
They ranged from:
3.5 lb to 9 lb
Two dogs with identical results at all five markers:
Dog | IGF1 | IGF1R | STC2 | GHR E191K | GHR P177L | Adult weight |
Dog A | II | GA | AA | AA | TT | 3.5 lb |
Dog B | II | GA | AA | AA | TT | 7 lb |
Same five results.
One dog is twice the weight of the other.
The most common combination, GG and TT, covered dogs from:
4.2 lb to 9 lb
So in our dogs, these five markers alone do not yet predict an individual Chihuahua's adult weight.
The genes are working. We just don't know all of them yet.
What we are still learning
Body size is controlled by many genes, not five.
Researchers have found dozens of regions linked to size in dogs.
Each one adds or takes away a little.
The five on a report are the big steps between breeds.
Inside the Chihuahua, most of those steps are already taken.
The differences between one Chihuahua and the next likely come from genes that are not on the test yet, and from how the known genes work together.
Food, health, and growth in the first months matter too.
Why "charting" doesn't work
Puppy weight charts are everywhere.
You weigh the puppy at a set age, then read an adult weight off the chart, or multiply by a set number.
They fail for Chihuahuas for five reasons.
1. They assume every puppy grows on the same curve.
Chihuahuas don't.
Some are done by 6 months.
Some keep filling out until 2 years.
Two puppies can weigh the same at 10 weeks and end up pounds apart.
2. They are built from averages.
An average hides the spread.
Our adults range from 3.5 to 9 pounds.
A chart drawn through the middle is wrong for the dogs at both ends, and those are the dogs buyers worry about.
3. Early weight reflects the litter, not just the puppy.
Birth weight depends on litter size, the dam, and her milk.
A puppy from a big litter can start small and catch up.
A puppy from a single-pup litter can start big and stop early.
4. Illness, parasites, and a slow week change the curve.
A chart can't tell a small puppy from a puppy that was sick.
5. Nobody tests the charts.
Most charts are never checked against real adult weights.
When we checked Embark's own predicted weight against real adults, it was within 1 pound for only 4 of 12 dogs.
The better answer: collect the genetics, and the real weights
Charting guesses from one number.
Genetics looks at what the puppy actually inherited.
DNA is the right tool.
We are still learning how to read it for size in Chihuahuas.
Most of today's five markers are the same in nearly every Chihuahua.
The genes that make one Chihuahua 4 pounds and another 7 are still being found.
The way to find them:
many Chihuahuas with both a DNA test and a real adult weight.
That is what SIPGS is building.
DNA results from every dog.
Adult weights from a scale, with the date and age.
Parents and grandparents linked in the pedigree.
With enough dogs, we can see which stretches of DNA travel with small adults and which travel with large ones.
That will predict size far better than any chart ever can.
How you can help
If your Chihuahua has an Embark test and is at least 1 year old, send us:
the Embark profile link
the dog's adult weight from a scale
the dog's age when weighed
Contact:
What does predict size
1. Parents and grandparents, weighed as adults
Real adult weights of the sire, dam, and grandparents are the best guide we have.
Ask for actual weights, not "about" or "predicted."
2. The puppy's own growth
A breeder who weighs every puppy, every week, can see where each one is heading.
Compare the puppy to its littermates and to earlier litters from the same parents.
3. Time
Some Chihuahuas reach full size by 6 months.
Others keep filling out until about 2 years.
About Embark's predicted adult weight:
It is a model, not a measurement.
We compared it with real adult weights for 12 of our dogs.
Dog | Embark predicted | Actual adult weight |
Dog A | 7 lb | 3.5 lb |
Dog B | 3 lb | 7 lb |
Dog C | 6 lb | 9 lb |
Dog D | 7 lb | 4.3 lb |
Dog E | 8 lb | 5.8 lb |
Dog F | 6 lb | 4.2 lb |
Dog G | 6 lb | 4.9 lb |
Dog H | 7 lb | 8 lb |
Dog I | 4 lb | 5 lb |
Dog J | 8 lb | 7.4 lb |
Dog K | 6 lb | 5.6 lb |
Dog L | 5 lb | 5.3 lb |
Only 4 of the 12 were within 1 pound.
Dogs A and B were predicted backwards: the "7 lb" dog is 3.5, and the "3 lb" dog is 7.
What to ask a breeder
What did the sire and dam weigh as adults?
What did the grandparents weigh?
What have past puppies from this pairing weighed as adults?
What does this puppy weigh now, and how fast is it gaining?
Tiny Chihuahuas need extra care
Adults under 3 pounds can be lovely companions.
They also need more care:
Higher risk of low blood sugar, especially as puppies. See our post on hypoglycemia.
More fragile bones.
Frequent small meals.
Closer vet follow-up.
A breeder who sells "teacup" size as a feature is selling a risk, not a guarantee.
Key takeaways
The AKC standard caps Chihuahuas at 6 pounds. There is no minimum.
In 238 Chihuahuas, IGF1 never varied, and GHR E191K and STC2 almost never did.
71% of Chihuahuas carry the "larger" IGF1R GG. It is the normal result in this breed.
IGF1R and GHR P177L vary. On their own, they did not yet predict adult weight in our dogs.
Embark's predicted weight was within 1 pound for only 4 of 12 of our adults.
Two dogs with identical size results weighed 3.5 and 7 pounds.
Size is controlled by many genes. We are still learning how they work.
The best guide is the real adult weight of the parents, grandparents, and past puppies.
Weight charts assume one growth curve. Chihuahuas don't grow on one curve.
The answer is more dogs with both DNA and a real adult weight. Send yours to SIPGS.
Sources
AKC Official Standard of the Chihuahua.
Rimbault M, et al. (2013). Derived variants at six genes explain nearly half of size reduction in dog breeds. Genome Research, 23(12):1985-1995.
Plassais J, et al. (2019). Whole genome sequencing of canids reveals genomic regions under selection and variants influencing morphology. Nature Communications, 10:1489.
Embark Veterinary. Body Size trait results: 106 original reports and 132 public profiles.
Stringer, T.A. (ongoing). Stringer Integrated Pedigree-Genomic Study (SIPGS). Scale weights, October 2026.
© 2026 A & A's Chihuahuas and Rev. T. Stringer. All rights reserved.
This educational content may not be reproduced without permission.
