Grab your sonic screwdriver and fire up the TARDIS, it's time to save the world in your own Eleventh Doctor's Jacket!
Doctor Who: Eleventh Doctor's Blazer - Sizing Chart
Measure all the way around your chest at its thickest point (just under your arms).
Measure around your torso at belly button height, NOT at belt height.
Measure from the outside tip of your shoulder, past your elbow, to your desired cuff length (keeping your arm slightly bent).
Measure from the base of your neck (where the bottom of your collar would be), to the desired hemline of the bottom of the garment.