1. Plan Your Boxed Depth

• Decide the finished depth of your bag base (common: 2–6 in).
• Convert the finished depth to your cut-out size: divide the desired finished base width by 2 (e.g., 4 in base = 2 in square cut-out).
• Note: This method works for two common constructions: cutting squares from corners, or marking a triangle across the seam and stitching.

2. Prep and Sew the Body Seams

• With right sides together, stitch the side seams and bottom seam of your bag exterior using your pattern’s seam allowance (often 1/2 in or 3/8 in).
• Press seams open to reduce bulk.
• Repeat for the lining if you’re making a lined bag, leaving an opening in the lining bottom for turning later.

3. Method A – Cut-Out Square Corners (fast and beginner-friendly)

• From each lower corner of the bag body (still wrong side out), measure and mark a square equal to half your desired base width (e.g., mark a 2 in x 2 in square for a 4 in base).
• Align the square so one side sits along the bottom edge and one side along the side edge.
• Carefully cut out the marked squares on both lower corners.
• Open each corner and pinch so the bottom seam lines up with the side seam, forming a flat triangle.
• Nest or butt the seams together; secure with clips.
• Check that the triangle’s opening measures exactly your cut-out size across; adjust if needed.
• Stitch across the corner perpendicular to the seam at your chosen seam allowance (commonly 1/2 in), backstitching at both ends.
• Optional: Trim the seam to reduce bulk and finish with zigzag or serger.

4. Method B – Sew-Then-Measure Triangle (no cut-out; great for directional prints)

• Leave corners uncut. From the corner, pull the layers apart and align the side seam with the bottom seam to form a triangle; finger-press flat.
• Use a ruler to measure from the tip of the triangle down along the seam; mark a line across the triangle where the width equals your desired boxed depth (the cross line length equals the finished base width; e.g., 4 in).
• Ensure the line is centered on the seam intersection and perfectly perpendicular to the seam.
• Stitch along the marked line and backstitch.
• Optional: Trim the excess triangle to 3/8–1/2 in and finish the raw edge, or leave it in place for added structure..

5. Repeat for All Corners

• Complete both lower corners of the exterior.
• Repeat for the lining corners (use the same measurements so the lining fits smoothly inside the exterior).

6. Press and Shape

• Press the boxed seams toward one side or open, depending on bulk and interfacing.
• Turn the bag right side out and gently shape the corners to square them.
• Check the bag stands evenly; if not, re-check measurements and seam alignment.

7. Finish the Bag Assembly

• Insert the lining into the exterior, right sides together; align side seams and top edge; stitch to attach as your pattern directs.
• Turn through the lining opening; press the top edge and edgestitch if desired.
• Close the lining opening with a narrow topstitc

8) Troubleshooting Common Issues

• Uneven base: Confirm both cut-outs or stitch lines are identical and seams were nested.
• Twisted corners: Ensure side and bottom seams align perfectly before stitching across.
• Bag won’t stand: Increase interfacing weight (foam or sturdier stabilizer) or increase boxed depth for a wider footprint.
• Fraying at corner seam: Finish trimmed seam allowances or use pinking shears on woven fabrics.