[Coda]

You deal with that by doing lots of measurements, making sure to add enough seam allowance (traditionally 3/8", some patterns use 1/4"), and cutting it too big and checking the size before trimming it down to size. Marking the fabric with a fabric pencil when you're planning can help -- I've been known to drape the fabric over my body and mark it up with a pencil or pins to get a rough shape and then laying it out to draw out some cleaner lines. Pinning the pieces together and trying them on is helpful too.

I've made a habit lately of drawing my designs out on newsprint before I start cutting fabric.