Once your drop cloth is washed and dried, cut out a square that is 45 inches on every side (or larger if you're opting for a larger tree skirt). Just make sure whatever size you make your tree skirt, it is the same measurement on every side, forming a square.
To cut your skirt into a circle, fold the square you just cut into 4ths (in half one way, then half another way). Divide whatever measurement you made in the previous step by 2.
In my case that number is 22.5 inches. So, I measured 22.5 inches down from the tip of the interior corner (the corner where there are no outside edges of fabric) and made a mark with tailors chalk. Then moved the measuring tape over 3 inches (while the top of the measuring tape is still at the interior corner tip) and made another mark. Repeat every 3 inches until the outline of the rounded curve is marked out
Then, cut along that curved line that was created.
To cut out the center circle for your tree stump, measure 3 inches from the interior corner tip on each side and then in the middle and mark with tailors chalk again, Then cut along that rounded line that's been created, forming a circle.
Now that your skirt is cut into a skirt shape, cut a line from the center to the edge to be able to wrap your skirt around the base of your tree. Set that piece aside.