How to Sew Box Corners, Sewing Boxed Corners Made Easy

Learn how to sew box corners for bags and purses. When you need to create some volume and shape in a bag, the best way to do that is to turn the corner into a box corner. By matching your side and bottom seams where the length and width of the bag meet, you can create a boxed corner.

How to Sew Box Corners Tutorial

This tutorial will show you how to sew box corners 2 easy ways.

What are Sewing Box Corners?

The box corner is a simple, straightforward sewing technique to square off the corner of the bag. This box action creates a gusset effect that gives depth and a greater volume to any bag or purse.

Sewing box corners on a fabric bag are easy to do and make a world of difference to the bag’s shape and capacity to hold all kinds of goodies.

Supplies for Sewing Box Corners

What you need for sewing a boxed corner:

• Sewing Basics - Sewing machine, iron, scissors, pins, ruler
• Fabric - Use cotton or other fabrics that are suited to sewing bags by machine. This could be cotton, cotton blends, linen, canvas, denim, and any other weight of fabric not requiring an industrial machine.
• Optional - Straps, buttons, zips, or velcro additions for closing the bag could be added according to the pattern and the design.

When to Use Box Corners in Sewing

Box corners are useful for tote bags, book bags, shopping bags, pillows, cushions, pillowcases, and creating comfortable cushions for outdoor benches or seats.  Wherever you think a shaped corner would make a difference to what you are sewing, there could be a box corner to suit your fabric project.

Calculate the Size of the Boxed Corner

The easiest way to calculate the boxed corner size is to decide on the depth of the bottom of the bag. Remember boxing the corners will lessen the height of the bag.

BOX CORNER FORMULA: Divide the finished depth of the bag measurement by two, and there you have the required measurement for the box corner.  Therefore, if your base is to be 4 inches, then each side of the box must be 2 inches.

A bag measuring 19” X 17” before boxed corners will change in size according to these measurements and the amount of fabric used for the box corners.

Here are some interesting box corner calculations for sizes and bag measurements and what they can be used for:

• 1” corners make a base of 2”, 17” width and 15” height.
• 3” corner make a base of 6”, 13" width and 13" height.
• 4” corner make a base of 8”, 11" width, and 12" height.

How to Sew Box Corners - Step by Step Instructions

Method 1 - Sewing Box Corner from Squares

A simple box corner can be created from square or rectangular pieces of fabric. Here is how to sew basic box corners:

Step 1 - Stitch the Bottom and Sides

Cut 2 pieces of fabric in a square or rectangle shape. Put the right sides together and sew the bottom and the sides with the required seam allowance.

Step 2 - Match the Seams

Press the seams open. Neaten the edges of the seams or trim with pinking shears.

Pull the fabric apart at the bottom of the bag to make the bottom seam flat and form a point at the end. You should match the bottom and side seams. Check inside the bag to see if the seams accurately match and pin it in place.

Step 3 - Mark and Stitch the Corner

Measure from the tip of the bag to the depth of the triangle base. Draw a line to mark the size of the base you require for the bag. The longer the measurement from the point of the seam to the baseline, the bigger the box area will be. 

Sew straight across this line on the stitching guide line. 

Step 4 - Trim the Box Corners

Depending on the bulk of the corner, you may want to trim the tip off and neaten the edges.

Repeat to box the corner of the other side.

Step 5 - Press

Pull your bag to the right side and press the sides and the box. The extra fullness created by the corner creates volume for the box or bottom of the bag.

Method 2 - Box Corners Cut Outs

Cutting a square out at the corner where the side seam and the bottom seam meet is another way of creating a box corner. 

Cut a rectangle of fabric and fold it in half. Cut a square in the corners to the desired depth. When using this method, accuracy in the cut width and length is important to get your desired size of the box.

If you open up your fabric, this is what the cut-out corner looks like.

Step 1 - Sew Side Seams

Put the fabric right sides together and sew the side of the bag with a straight stitch. Neaten the seams if you are not lining the bag. Press open the seams.

Step 2 - Sew the Box Corners

Pull open the cut edges of the square and match the side seam with the bottom. Sew across the matched edges of the cut corners and neaten if necessary.

Step 3 - Turn Right Way Out

Pull the bag the right way and push out the corners before pressing the bag. 

If you did not line the bag, you will need to create a simple hem at the top edge before stitching on your handles. Bag patterns may vary with different finishing touches, but the box corners will always be the same.

How to Sew Box Corners - In Conclusion

Learning how to sew box corners make the difference between a bag that looks a bit like a sack and a bag that is finished with a professional touch and has the depth or base to hold your goodies comfortably.