How can you tell if your garment has a good hem?

A good hem on a dress or a skirt should be almost undetectable. Stitches should be spaced just far apart enough to support the hem, not too close together to pucker the fabric and not too far apart so as to gap. The deeper a hem, the better it hangs (2" to 3", depending on the style and the fabric). The more shallow a hem, the more likely it will roll; just look at how the hem rolls on a new pair of jeans after you wash them the first time. Also, if the weave of the fabric tends to fray, the raw edge of the hem needs to be prepared (either attach hem binding or apply stitching to prevent fraying).
A good hem on a dress or a skirt should be almost undetectable. Stitches should be spaced just far apart enough to support the hem, not too close together to pucker the fabric and not too far apart so as to gap. The deeper a hem, the better it hangs (2" to 3", depending on the style and the fabric). The more shallow a hem, the more likely it will roll; just look at how the hem rolls on a new pair of jeans after you wash them the first time. Also, if the weave of the fabric tends to fray, the raw edge of the hem needs to be prepared (either attach hem binding or apply stitching to prevent fraying).