I normally prefer a 2" cut for a box bottom, I just like that size, but adjusted that to 1 1/2" in these examples, due to a large pocket on the front. This will make about a 3" depth on the tote. Keep in mind that as you gain depth with your box bottom, you will lose that in height and width.
First Method: Turn your bag inside out. Lay your bag flat and measure out a 1 1/2" square on each corner (not including any seams), carefully cut out the square, your bag should look something like this.
Fold the cut ends together and stitch together using a 1/4" seam allowance, reinforce the seam to prevent fraying. Turn your bag right side out.
Second Method: Turn your bag inside out. Fold the bottom corners of your bag into a triangle. Make sure the side seam and bottom seam line up (or if there is no seam at th bottom, then the crease). Measure 1 1/2" in from the point (not including the seam), making sure your line is perpendicular to the seam, sew a line straight across.
Cut off the extra fabric, reinforce the seam. Turn right side out.
Now, slip in your notebook and latest craft project, and you're ready to sport your stylish new box bottom tote bag.
Until next time, Happy Crafting!