A suit jacket can sometimes be let out if there is usable seam allowance in the required area. Available fabric, previous alterations and the jacket's construction determine the result. A size label alone cannot tell you how much extra room is possible.
Locate the actual restriction
Wear your normal shirt and fasten the working button. Identify whether tightness is at the waist, chest, upper back or arms. A waist adjustment will not necessarily solve restricted shoulder movement. Do not request an all-over enlargement without a fitting assessment.
A tailor should inspect the inside seams and lining. Existing stitch marks, fabric fading and trim placement can make a change visible even when extra cloth is available. Ask what the exterior will look like after alteration.
Evaluate the complete proposal
Letting out one seam may affect the shape of nearby panels. The lining may also need adjustment. Pockets, vents and side seams place practical limits on how the change can be distributed.
Agree a realistic target measurement and test the jacket in ordinary movement. If you need space for a thicker underlayer, wear it during the fitting. An alteration approved over a thin shirt may not solve a layering problem.
How much can be added?
There is no reliable universal amount. The tailor must inspect the garment. If there is little allowance or the shoulders are too narrow, another size or cut may be more practical. Avoid buying a tight jacket solely because someone says all suit jackets can be enlarged.
Related reading
Agreeing jacket measurement methods and tolerances. For another useful reference, see How to document jacket sample approval.
