Cut length needed for a double-fold hem.
Double-fold hems turn under twice, adding twice the hem depth to the cut.
A double fold hem turns the raw edge under twice, so the cut length must include the finished length plus twice the hem depth. For a finished length of 30 inches with a one inch hem, cut the fabric 32 inches long. Enter the finished length and the hem depth to find the cut length.
Hem depth depends on the garment and the fabric. A narrow hem of a quarter to a half inch suits light fabrics and curved edges, while a wider hem of one to two inches adds weight that helps skirts and curtains hang well. Very deep hems on curved edges can ripple, since the outer edge is longer than the inner.
Press each fold carefully before you sew so the hem stays even, and measure from the fold, not from the raw edge. Allow for any shrinkage by prewashing the fabric, and cut a little extra if you are not sure of the final length.
You can finish the hem by machine for a visible line of stitching, or by hand or a blind hem stitch for an almost invisible result. Check the fabric on a scrap first to see which finish looks best.