Alteration prices seem inconsistent to customers because they track something invisible. The cost driver is how much of a garment must be taken apart, not how much is moved.
The work is disassembly and reassembly
Changing a garment usually means opening existing seams, removing linings or facings, adjusting the piece, and rebuilding what was opened in the correct order.
The visible adjustment might be a small distance, but reaching the seam that controls it can require unpicking several other components first.
Pricing therefore tracks the depth of the intervention, which is why a change described in inches gives no indication of what it will cost.
Construction determines what is possible
Garments contain seam allowances, the fabric beyond the stitch line. Generous allowances permit letting out; minimal allowances mean the garment can only be taken in.
Mass production has reduced allowances to save fabric, so many modern garments cannot be enlarged at all regardless of the tailor's skill.
Fused interfacings, bonded seams and knit constructions further limit options, since some cannot be reopened and restitched without visible damage.
Some alterations change the design
Shortening a straight skirt is a simple hem change. Shortening a flared or bias-cut skirt changes the width at the hem and can alter how the garment hangs.
Sleeve length on a jacket with buttons or a shaped cuff must often be adjusted at the shoulder instead, which is among the most involved alterations available.
A tailor quoting a high price for a small-sounding change is usually describing this: the adjustment requires rebuilding a structural part of the garment.
Fit priority follows a fixed order
Shoulders and the upper back are difficult and expensive to alter, so garments are generally selected to fit there and adjusted elsewhere.
Waist, length and taper are comparatively straightforward, which is why buying for the largest measurement and taking in is standard practice.
Understanding this order changes purchasing decisions, since a garment that fits the shoulders and is loose elsewhere is a better candidate than the reverse.
The arithmetic favors fewer, better garments
Alteration cost is roughly independent of what the garment cost, so the same work represents a large share of an inexpensive item and a small share of an expensive one.
That relationship pushes tailoring toward pieces intended to last, where the cost is spread across many wears rather than a season.
It also explains the persistent advice to buy less and adjust what is kept, which is an economic observation before it is an aesthetic one.