Choose the trouser hem with your shoes on
Trouser length is a relationship between the fabric, the shoe and the way you move. A hem that works with a thicker sole can skim the pavement with flats. Check the two together before saving the combination or deciding a pair needs tailoring.
Set up two real shoe options
Put on the trousers with the shoes you wear most often. Stand naturally and check the front, side and back. If you rotate between two shoe heights, try both pairs. A flare that nearly touches the ground standing can brush it during a stride; a narrow leg may instead catch on a high boot. Choose the hem that works for your common route and reserve the other pairing for days when it makes sense.
Test beyond the mirror
Walk a few steps, sit down and take a step up. See whether the back hem gets caught under your heel and how much ankle shows when you sit. A temporary fold can help you compare lengths at home. Use a proper alteration if you want a lasting change, and check the garment’s care instructions before measuring a new hem.
Record the pairing you tested
Write “blue flares with thick-soled sneakers” instead of simply “blue jeans.” If you need to wear flats, save a different bottom with them. That makes the outfit easier to repeat without redoing the fit test every morning.