Weigh him on a kitchen food scale? Adult dragons usually weigh 300 grams and up- he looks good but they all have different weights - you dont want him over 400 grams -
He looks healthy in those photos. As mentioned, using a kitchen scale that can measure grams is the easiest way to weigh them. Then just keep a log or spreadsheet of the measurements so you can track his weight over time. The important thing is to watch how his weight is trending. There will be some small fluctuations, but his weight should remain pretty stable over time.
He looks a good weight, well proportioned , not too fat or too thin. A proper weight will differ with body length, a 20 " inch or longer will usually weigh more. Adults are almost always over 350 grams but can range up to 500-600 or a little more if they are over 20" long.