Get a roll of parchment paper. Ideally, you'd like to have a 20 inch diameter circle when you're finished cutting the paper but 12 inch wide & 15 inch wide paper is more readily available.

Lay the sheet on a flat surface. You're going to fold it 4 times.

Fold #1: In half creating a rectangle

Fold #2 In half creating a rectangle

Fold #3 In half beginning to create a triangle

Fold #4 In half creating a triangle

Place the point of the folded paper in the center inside the bottom of the Dutch oven.

Use your hand to flatten the paper against the bottom and up the wall of the oven.

Use scissors to cut the excess paper. You are actually going to be cutting the paper into a circular shape that is large enough to cover the floor and at least 3/4 of the way up the inside walls of your Dutch oven.

I actually like mine a little larger so some paper hangs over the edge of the oven and beyond the lid. That way I can use the exposed paper as "handles" to remove hot food from the hot oven to cool.

Unfold the paper.

Place the cut paper into your Dutch oven and form it around, pressing the paper along the bottom and up the sides. You want to create a crease in the paper around the edge where the bottom of the oven meets the wall. Then, see how it fits.

When you confirm the first paper fits the oven, fold it back into the triangle pie shape. You're going to use it to make a pattern so you can repeat the process to make as many liners as you need.

You will do the 4 folds on each piece of parchment, then use the pattern so you are trimming the correct amount from each piece of paper.