I was lucky when I bought one of the pretty Mexican dresses because it fit me really well and I could take the measurements off of it to reproduce it in my sewing room. If you don’t have a dress to copy for yourself, you will have to find out about how much ease you want in the dress or blouse. This can take some trial and error. I thought I would see how much ease is in my dress compared to my measurements.
First, I tried the dress on and found out that the total width of the dress is about 10-12 inches larger than my hip measurement. This means that there is an extra 5 to 6 inches of width in the front and the same in the back. This will give you an idea of where to start, but the ease can be adjusted depending on how close fitting or loose you want the dress to be.
In the drawing above, you can see how the dress hangs on the body. The shoulders are wider than the natural shoulder line forming a dropped shoulder. Since you will be pleating or gathering the top of the body piece onto the bottom of the yoke, the measurement you need is the width of the bottom of the yoke. Measure from the middle of the underarm across the chest above the bust to the other side middle of the underarm. Of course, seam allowances and any ease you want should be added to this measurement.
The drawing of the dress in red shows the more modern type of sleeve with the triangular gusset section grafted onto the rectangular sleeve piece. The drawing below shows a separate piece for the gusset. You can refer to my other posts to see how to sew in a gusset if you want to go the old traditional route, and to get an idea of how low the armhole is in my dress. It seems to be about 4 1/2 to 6 inches below the finished bottom yoke line.
I hope this helps you on your way to a comfortable and pretty Mexican blouse.