A package just arrived at your doorstep secured with recognizable yellow and red tape. It is a size run of samples from your factory! You unbox them and get out your measuring tape. To double check that the sizing is right, you need a:
A) Size chart
B) Graded spec chart
C) Grade rule
D) Person to try on each size
E) A good gut feeling
Half the time when designers say they need help creating a size chart, what they really mean is that they need a spec chart for their design. It is understandable. There are many similar terms (size chart, spec chart, spec sheet, graded spec, POMs) and they are all a spreadsheet of numbers with sizes. There is a difference between them, though.
One of my most popular blog articles dives into the differences and how to use each one in your fashion business.
P.S. (The answer above is “B”. You want to check the finished garment measurements against the graded spec chart to confirm that each size measures what it should.)