This simple tutorial has been designed for the Edie cardigan, though you could apply the same principle to any sleeve pattern piece.
If you are planning to make your Edie cardigan in a thick fabric so that it is more of a “coatigan”, you may wish to widen the sleeves a little to make sure you can still comfortably wear it over a long-sleeved top.
One way to do it is to simply grade your sleeve to the next size up, starting at the armscye. The simplest way to do this is by using a French curve, but if you don’t have one you can draw your own curve. Since the sleeve is cut on the fold, any curve you draw/cut will be mirrored.
The other way is also very simple, though takes a little more measuring. Decide how much you want to increase your sleeve width by (1cm/ 3/8″ should be plenty if the sleeve is cut on the fold, 1cm/ 3/8″ on each side if you are working with a full sleeve piece).
Identify the narrowest point of the curve from the armscye, and measure out 1cm/ 3/8″ from here. Also measure a point 1cm/ 3/8″ from the sleeve hem. Join these two points with a French curve. If you don’t have a French curve, make more marks all along the sleeve edge at 1cm/ 3/8″ away from your pattern piece, and then join up these marks to finish.
The upper part of the sleeve will need to be graded from the armscye point to the top of your new line. The simplest way to do this is with a French curve again: use your French curve to join the armscye point to the upper point you first drew (do not let out the armscye, as then your sleeve piece won’t fit the bodice of your garment!) If you do not have a French curve, you will need to create a smooth curve. A little below the armscye, measure out a couple of millimetres/ 1/8″, then a little lower down a few more millimetres/ 1/4″, and then draw a line from the armscye point to the top of your new line, making sure that the line you draw passes through all the points you have made.
This is now your new, widened sleeve piece! Cut as directed.