Finn is almost eight months and at his last vet visit in mid June he weighed 9 pounds. Is he under weight or is this an acceptable number for his breed (Jack Russell mix) and age?

It's great that you're keeping a close eye on Finn's growth — that's exactly the kind of attentiveness that keeps a young dog healthy!

As general information, Jack Russell Terriers are naturally small, compact dogs. Fully grown adults typically weigh somewhere in the 6–8 pound range on the lighter end, up to about 13–17 pounds on the stockier side, depending on their build and any mix in their background. So at 9 pounds at around 7 months, Finn is in a range that sounds plausible for the breed — but whether it's right for him specifically depends on a lot of factors a scale alone can't tell you.

A few things that matter more than the number on the scale:

• Body condition — You should be able to feel his ribs easily but not see them prominently. He should have a visible waist when viewed from above, and a slight tuck in the belly when viewed from the side.
• Energy and coat — A puppy at a healthy weight is generally active, curious, and has a shiny coat.
• Growth curve — A single weight snapshot is less informative than knowing whether he's been gaining steadily. At 7–8 months, most small-breed dogs are close to or at their adult size, so his growth rate should be slowing down.
• Mix factor — Since Finn is described as a Jack Russell mix, his ideal adult weight could vary quite a bit depending on what else is in his background.

Some at-home things you can do right now:

• Run your hands gently along his sides — ribs should be easy to feel with light pressure, like the back of your hand
• Look at him from above — a healthy dog has an hourglass shape, not a barrel shape or a bony, angular look
• Check that he's eating consistently and enthusiastically

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When to see your vet:

Since Finn's last weigh-in was in mid-June, it's worth mentioning your weight concern at his next scheduled visit — or calling the clinic to ask if they'd like to do a quick weight check in the meantime. Definitely reach out sooner if you notice any of the following:

• He seems to be losing weight or eating less than usual
• His ribs, hip bones, or spine are visibly prominent
• He's low energy, vomiting, or has loose stools
• His coat looks dull or patchy

Your vet can look at his full growth history, feel his body condition firsthand, and give you a much more personalized answer than any number on a scale can. They may also have thoughts on whether his current food and feeding schedule are a good fit for where he is in his development. 🐾