Q: I have a garment that’s too small, can you make it bigger?
When It's too small:
When a garment is too small, there’s only so much it can be let out and this depends on how much extra fabric is left at the seam. The extra fabric that extends past a seam, is called seam allowance, and the seam allowance indicates whether a garment can get any larger.
Letting out the waist on pants or skirts is usually possible by a size - especially suiting. Because suits are expensive, enough seam allowance (to let out one size) is generally left. Also on the inseam of pants, one of the seam allowances is usually more generous, and this allows the leg and crotch depth of the pant to increase in size. To find the seam allowance turn your garment inside out and look at the extra material that's along the edge seam and what is left at the bottom seam (if you need the garment to be lengthened).
A good rule of thumb is: if a garment needs to grow by 1/2 a size - chances are good it will be possible. Anything more than that and there’s no guarantee.
*It's always better to buy something that’s a bit big than a bit small
Lot’s of people are between sizes, and there’s nothing wrong with that! Buy the larger size, and have it taken in to fit your shape.