[Fodder]

Call around to pet stores… some have scales. Pet Food Express has them if you’re in Western states…. Petsmart if they have a Banfield attached… otherwise I’ve seen them at some smaller / independent store but inconsistently.

Honestly, feel is going to be better than any number - if you’re certain he’s gaining (and it’s not his winter coat), more exercise, less food, or both.

 

[Fodder]

Ask your vet staff if you can come in just to weigh your dog. Most will accommodate for free and as long as they aren't super busy. Calling ahead is welcome as well.
It accomplishes 2 things. You get your dog weighed and your dog doesn't learn to associate the vet office with all bad things. Get weighed, get a treat and pets and leave on a good note.
Both of my vets allow free weight checks. One has the scale in the waiting area so we can pop in, say hi and do a weight and be on our way in a few minutes.
As has been mentioned, many pet stores have scales for use. There accuracy may not be great but you'll get an idea.
The other option is to buy your own pet scale to have at home to use at your convenience if it's in the budget.

this would definitely be my first choice too… but i assumed the vet was inconvenient or the dog has a strong aversion.

nice thing about pet store scales - i can always grab a bag of food to put on the scale first to check for accuracy. my local store is great tho - they’re required to calibrate their scale on a schedule.