As many as you want!
Good news! As of 9/9/2020, here is no limit to how many Wyze scales you can add to one Wyze account. Put a Wyze Scale in every bathroom, and in your home gym, too. 💪
To add additional scales to your account, repeat the steps in the Wyze Scale Setup Guide for each new scale.
Related article: How do I share my Wyze Scale?