I'm assuming you're cutting a full circle skirt. To help keep things symmetrical, I fold my fabric in half (hotdog way), then half again (hamburger way), then draw out an arch from the folded corner representing 1/4 of the total circumference of my desired waist. That way you're making one cut that cuts the fabric in an even full circle.
Also depending on your fabric you may need to cut your circle circumference smaller than your actual measurement. Because of the fabric grain/bias issues lunaflora mentioned above, circle skirts have a tendency to stretch out once they're hung and it's much easier to cut your waist circle bigger than to try and make it smaller.
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