Measure from the shoulder
An abaya hangs from the shoulders, so that is where the measurement starts. Stand straight in the shoes you wear most days and ask someone to hold a tape at the top of your shoulder, where a seam would sit. Let it fall straight down to the point where you want the hem to end.
Write the number down in inches. That single figure is your abaya length, and it matters more than any other measurement: a loose cut forgives a lot around the body, but not at the hem.
Decide where the hem should fall
For everyday wear, most women like the hem to clear the floor by an inch or two. It stays clean on wet streets, it does not catch on stairs or rickshaw steps, and you can walk quickly without lifting it.
For occasions, a longer hem that just brushes the top of the shoe looks more formal. If you wear heels for events and flat sandals every day, measure in each and keep both numbers.
Check against one you already own
The easiest shortcut is an abaya that already fits you well. Lay it flat, measure from the shoulder seam straight down to the hem, and use that number. If it always felt a little short or a little long, adjust by an inch.
Reading NOORA sizes
NOORA sizes are named by full length, shoulder to hem: S is 52″, M 54″, L 56″ and XL 58″. Choose the length nearest to your number. If you fall between two, take the longer one for occasions and the shorter one for busy days.