Turn the garment inside out to check the extra cloth at the seams and hems before taking on an alteration. A seam allowance is the fabric between the original stitch line and the cut or overlocked edge. To gain room, you need enough usable fabric beyond that line to sew a new one securely.
Work out where the fit is tight
Check waist, hip, shoulder and length separately. Extra fabric at the hem cannot solve a tight waist. Look for a waistband seam, darts, belt loops, pockets or a lining that would also have to move. A separate elastic adjustment may give more room without disturbing the seams. If the wearer cannot sit or move comfortably, identify the restriction before agreeing to alter the piece.
Measure the shallowest part of the allowance
Check both fabric edges along the part of the seam you would move. Factory overlocking close to the stitching may leave little to use. Example: if you have 12 mm from the stitch line to the sound edge, and the fabric and seam finish need 8 mm left inside, the new stitch line can move only about 4 mm on that edge. Moving both edges out by 4 mm adds about 8 mm at that seam in this example. Do not use the example as a universal minimum.
Look for signs the garment has already been altered
A second line of holes, different thread colours or an uneven raw edge can indicate past work. The old stitching may have left a visible line on the outside. Check whether the seam becomes narrower where it meets a pocket or waistband. Letting out only the middle without a smooth transition can distort the shape.
Decide before paying or unpicking
Photograph or write down the measurements if the shop permits. If the amount you need is close to the available allowance, or a lining or zip blocks access, ask for an alterations assessment. For length only, measure the existing turn-up separately. A garment that fits now with a modest, clearly accessible adjustment is easier to assess than one that relies on several seams all moving as hoped.
References
- New Mexico State University Extension — Making Perfect Garment Hems
- The Alteration Shop — school uniform repair and alterations
- Middle Park Primary School — uniform and second-hand stall