These are measurements of the jersey laid flat, not of your body. The most
reliable way to pick a size is to measure a shirt you already like wearing and
match it to the table.
Width. Lay the shirt flat and measure straight across from
one underarm seam to the other.
Length. Measure from the highest point of the shoulder,
next to the collar, straight down to the hem.
A variance of up to 0.75 inches from the chart is normal on a
printed-to-order garment.