Difference in weight from Cura to printed model
The density of the filament can be specified in the material model of the filament in Cura (Preferences -&gt; Configure Cura... -&gt; Materials and click on the material/filament you are using to slice your model for PETG), look at the value behind Density, the PETG filament I use is using 1.28 g/cm³ (PETG Economy Black -&gt; Specification &gt;).

This field is user editable, so you can change it to your needs. Cura calculates the weight based on the deposited volume.