A suit jacket should sit naturally at the shoulders, close without obvious strain and remain comfortable during ordinary movement. Fit should be judged with the shirt and trousers you intend to wear. A neat standing photograph is only one part of the assessment.
Check the frame before the details
Look at the collar and shoulder line from the front and back. The collar should rest comfortably rather than stand away conspicuously. Shoulder padding and sleeve construction vary, so compare the jacket's intended shape with your posture. Persistent dents or pulling deserve a different size or cut.
Close the intended button and inspect the chest and waist. Strong radiating tension lines suggest insufficient room. Extra room in a relaxed cut can be deliberate, but it should not leave the collar and shoulders unsupported.
Test length and movement
Sit, reach forward and bend your elbows. Check whether the jacket pulls across the back or forces the collar upward. Some movement is normal in a tailored garment, but discomfort should not be ignored. Review sleeve length with your normal shirt cuffs.
Assess the hem against the trousers and your body proportions. Shortening a jacket can disturb pocket placement and button balance, so avoid buying a poor overall length on the assumption that every detail can be altered easily.
Which changes should a tailor assess?
Sleeves and modest waist adjustments may be more straightforward than reshaping shoulders. Ask about the exact construction, seam allowance and finished measurements. If several major areas fit poorly, try another pattern before committing to extensive alterations.
Related reading
Agreeing jacket measurement methods and tolerances. For another useful reference, see Wearing a polo shirt with a blazer.
