Judge a suit jacket’s length from the whole outfit, with the trousers and shoes you intend to wear. The hem changes how much of the trousers is visible and how the upper and lower halves relate. Begin with a relaxed standing view, then check the back, side and ordinary movement.
Use seat coverage as a reference
For a conventional tailored silhouette, start by looking at the jacket from behind. Suitsupply’s jacket-fitting guide uses a hem that just covers the seat as its reference. This gives you a concrete place to begin comparing lengths.
Treat that as guidance for the look being described, rather than a requirement for every cropped or deliberately oversized design. Decide whether you want a conventional suit proportion or a different silhouette. A jacket can depart from the reference intentionally; the useful question is whether you like the result with your clothes.
Compare the front and back together
Stand naturally with your arms relaxed and the jacket fastened as intended. View the hem, lapels, button position and visible trousers together. Keep the waistband at its normal wearing position. Our button-stance guide looks more closely at the relationship between the fastening and the cloth below it.
Use the same shirt, trousers, shoes and mirror distance when comparing two jackets. Take front, side and rear views if photographs help. Note where each hem falls rather than deciding from a close-up or from how far your fingers reach; arm length is only one part of your proportions.
Check how the jacket behaves in use
Walk a few steps, sit, then stand and let the garment settle again. Notice whether you repeatedly pull the hem down or rearrange the back. Record what happens rather than assuming that length alone explains it; width, vents and the rest of the cut also need assessment.
If you normally wear an overcoat, try it over the chosen jacket. Check the relationship between the two hems and whether the layers move comfortably together. Our overcoat fitting guide takes that comparison further. A preferred jacket length should work in the outfits you actually use.
Assess alterations before committing
Proper Cloth’s back-length guidance warns that shortening can change the relationship of pockets, buttons and vents to the hem. It also notes insufficient material for lengthening its jackets. Ask a tailor to inspect the particular garment before buying it on an alteration assumption.
If the change would be substantial, compare another length or cut first. Choose the jacket whose overall proportions already come closest to your preference, then discuss any remaining adjustments. Continue through Watches & Wear for related fitting guides.