How to Easily Sew Any Size Boxy Pouch - The Math Formula Explained

Ever wondered how to do the maths to make a boxy pouch any size you want? Here’s how to do it. It’s quite simple actually. (Alternatively, if you want instructions on how to sew these pouches, head to the Pouch Pattern Calculator.)

Free Pouch Pattern Calculator - Here's how to do the math to make any size boxy pouch.
Free Pouch Pattern Calculator - Here's the math on how to make a pouch any size you want.

To figure out what length to cut the pattern piece, add your desired finished length to your desired height, plus four times the seam allowance you are going to use (if you are not using French seams, only use two times the seam allowance). The width of the pattern piece is two times your desired width plus two times your desired height plus two times the seam allowance.

Here’s an example:

Let’s say I want a pouch 8” long, 4” wide, 3” high, and to use a 0.5” seam allowance.

Length (of pattern piece) = 8” + 3” + (4 x 0.5”) = 13”

Width (of pattern piece) = (2 x 4”) + (2 x 3”) + (2 x 0.5”) = 15”

How to sew any size boxy pouch - the math made easy. By Sarah Kirsten
How to easily sew a boxy pouch any size you want - the math formula explained. By Sarah Kirsten

It’s slightly confusing because often the length of the pouch turns out to be the shorter sides of the pattern piece (not in every case however… it depends what dimensions you design your pouch). Don’t let that confuse you though. The “width” of the pattern piece is so long because it functions as the top, bottom, and both sides of the pouch while the “length” only functions as the length and half the height on each side.

Important note on the sewing: If you are using French seams on the corners, be sure that the height of the first seam on each corners is one seam allowance width shorter than your desired finished height - otherwise the pouch will turn out higher but narrower and shorter than you wanted. For example, if you want the pouch to be 5” high and are using a seam allowance of 0.5”, sew across the corners where the height is 4.5” To see a visual explanation of what I’m talking about, head to the Pouch Pattern Calculator page and look at step 9 of the pattern instructions.

If this math doesn’t look fun to you, check out my free Pouch Pattern Calculator I put together. You simply enter your desired finished length, width, height, and seam allowance and it tells you what size to cut the fabric! There are also step-by-step illustrated instructions on how to sew the pouch with lining using the French seam method that my sister and like to use.

Happy pouching! And mathing, if maths make you happy :)