Hi @michielXWZ7U. It sounds like you just need to get the 'perimeter' of a face on your part. The quickest & simplest way to do that is to use the Measure command. The Measure tool can be found in multiple places in Inventor's user interface. Most ribbons tabs for modeling, such as the "3D Model" tab, or the "Sheet Metal" tab either do, or can be showing the Measure panel, which shows the Measure tool. Or you can often just right-click anywhere in empty model space, and choose Measure from the right-click menu. Once that tool is active, just left-click on a part face, and it will usually show you both the perimeter and the area of the face in the little dialog. And if there are any cutouts in the interior of the face, the measure dialog will usually also show the 'Total Loop Length', which is the exterior Perimeter, plus the interior cutouts perimeters. Those values are select-able and copy-able. You can also use an iLogic rule to measure a part face, and can then either just display the resulting value, or write the value to a parameter or iProperty.
Wesley Crihfield

(Not an Autodesk Employee)