Have you measured your yorkie? The 7.25 inch is a very small measurement for a chest. So I would think if this is the measurement on the size of shirt you are looking at it would fit a very small yorkie. There really isn't a "most common" size, yorkies here at YT have ranged from approximately 2.5 lbs to 15 lbs. I don't know if this really answers your question or not though.
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