Bag Calculator

To cut the correct amount of fabric, the calculator accounts for the final width, height, and depth of your bag, adding standard seam allowances. The math is broken down into three core equations: First, the required fabric width is determined by taking twice the finished width plus twice the finished depth, plus an extra inch for side seams and breathing room: fabric_width = (2 * width) + (2 * depth) + 1. Second, the fabric height adds the finished height to half of the depth, plus an extra inch for top hems and bottom assembly: fabric_height = height + (0.5 * depth) + 1. Finally, the box corners—which give the bag its flat, structured bottom—are calculated by dividing the depth by two: box_corner = depth / 2.

Let us walk through creating a medium utility bag with a finished width of 14 inches, a height of 12 inches, and a depth of 6 inches. First, we calculate the required fabric width: (2 * 14) + (2 * 6) + 1 = 28 + 12 + 1 = 41 inches wide. Next, we determine the fabric height: 12 + (0.5 * 6) + 1 = 12 + 3 + 1 = 16 inches high. Finally, for the box corners to create the flat bottom, we divide the depth by two: 6 / 2 = 3 inches. Therefore, you will need to cut your fabric panels to 41 inches by 16 inches and cut out 3-inch by 3-inch squares from the bottom corners.

Always pre-wash your fabric before measuring and cutting, as natural fibers like cotton and canvas tend to shrink during their first wash cycle. Keep in mind that the formulas include a standard one-inch total allowance; if you plan to use bulky batting or heavy interfacing, consider adding an extra quarter-inch to your dimensions to ensure a smooth fit. Double-check your measurements before cutting into expensive textiles.