sew a zipper fly on jeans and pants



How to sew a zipper fly on jeans and pants

Does sewing a zipper fly make you shiver?

How come sewists are scared stiff when sewing a zipper fly on jeans and pants?

A zipper fly consists of three parts; the shield, the zipper, and the facing. Three small pattern pieces don’t seem like a lot to handle. Still, the sheer thought of a zipper fly can intimidate the most hardened seamstress.

We’ve all been there.

But, it doesn’t have to be a thriller.

This post breaks down the process into tiny steps. Read on, and soon you’ll sew a zipper fly on any jeans or pants like you’ve done nothing else before.

So, gather your courage, and let’s jump into it, shall we?

The parts of a zipper fly

The fly facing

the fly facing

Either cut as one with the pattern front or as a separate piece. Cutting it as one with the front saves you the bulk of stacked seam allowances in a small space and makes it slightly smoother to sew over. 

However, cutting two opposite curves, the crotch and facing, in one line can be a challenge. Test both ways and see which one you like better.

The curved seam, visible from the facing side, keeps the fly facing from moving. Industry-standard place the topstitch 3.5 centimeters/ 1 ⅜ inch and the edgestitch 3-5 millimeters / ⅛-¼ inch in from the fly’s front edge.

There are several ways to sew the topstitching and to get the stitches even. The simplest is to mark the fabric using a template and sewing the second stitch line following the first row of stitches as a guide. Sewing slow and at a steady pace also helps.

The zipper

different types of fly zippers

The zipper is sandwiched between the facing and the shield. It’s attached at the waist and with a visible topstitch on the front. Match the zipper to your fabric weight and color, and make sure it has a stop at the bottom to keep it from separating when open.

Both the zipper tape and the zipper teeth, or coil’s, width varies. Use metal teeth for jeans and polyester coils for pants. A standard jean zipper is 2.5-3 centimeter/ 1-1 ¼ inch wide, with 4-6 millimeter/ ⅛-¼ inch wide teeth.

The length should cover the pattern’s fly opening, and the zipper tape extends 1.5 centimeters / ⅝ inch below and above the zipper. 

Get a zipper with as wide zipper tape as possible; it gives enough room to sew most of it with a regular presser foot and saves you a lot of fiddling.

The fly shield 

the fly shield

The fly shield protects the wearer from the zipper teeth and functions as a backing to keep it in place.

The width is up to you, but the industry standard on a pair of jeans is 11-12 centimeter / 4 ¼-¾ inch wide before it’s folded, including 1 centimeter of seam allowance around the three sides.  It should also be wide enough to cover the fly facing.

The length is as long as needed to cover the zipper opening, which should be clearly marked on the pattern. It ends around 5-6.5 centimeters / 2-2.5 inches in from the crotch seam’s intersecting inseam to open and close comfortably and has 1.5 centimeters / ⅝ inch seam allowance at the waist. 

The fly shield is sometimes cut as a square, and sometimes with a slight inward angle at the center of the bottom, to reduce loose fabric inside the garment when it’s sewn.

Tools and Supplies

Everything you need to sew a perfect zipper fly.

supply list to sew a jean zipper fly

Prepare to sew the zipper fly

  1. Staystitch the waist.
  2. Overcast the sides and inseams. Leave the seam allowance intact.
  3. Press fusible interfacing to the wrong side of the fly facing (fused side up it looks like a J) and overcast the curved edge.
  4. Fold the fly shield right sides together and sew the bottom edge. Turn the right side out, press, and overcast the long edge to close it.
  5. Overcast the center front. Leave the seam allowance intact.


Sewing terminology in this tutorial.

glossary for this tutorial

Zipper fly tutorial

Sew the fly facing

  1. Lay the left front (as worn), so the waist is towards you.  Line up and pin the fly facing on the center front, right sides together.

pin facing to center front

2. Attach the fly facing with a straight stitch and 1 centimeter / ⅜ inch seam allowance.

sew the facing to the front

3. Press the seam open and press in the seam allowance of the crotch all the way to the edge.

press the seam allowance open

4. Flip the right side up, fold the fly facing under, and press from the right side. The turn of cloth should cover the seam when looking from the right side. Edgestitch the fly facing in place, from the crotch to the waist.

fold under and edge stitch

5. Pivot your work, so the waist is towards you. Fold up the fly facing and place the zipper on it, right sides together. With the zipper pull faced down, pin the left-hand side of the zipper.

pin zipper to facing

6. Sew the right-hand side of the zipper then pivot your work again.

attach zipper to facing

Add topstitching

7. With the wrong side up, fold in the fly facing and baste or pin the bottom right-hand side edge of the zipper so it’s out of the way from the presser foot as you proceed with the topstitches.

pin or baste zipper leg

The edge needs to be free from stitches when sewn to the fly shield in the next stage.

pin closeup

TIPS! Trace your fly facing pattern piece and cut away the 1 centimeter / ⅜ inch seam allowance on the sides. Now you have a template with the perfect size and angle to draw a guide for your topstitches.

make a zipper fly topstitching template

8. Draw a guide for the topstitching on the front’s facing side using chalk. End the curve at least 1 centimeter / ⅜ inch below the zipper to avoid sewing over the pin, but still catching the fly facing with the stitches.

mark the zipper curve with chalk

9. Topstitch, from the waist down, following the chalked guide. At the end of the curve, pivot your work and sew 2-3 stitches in the previous edge stitches. Pivot again, and sew the second row of stitches 4 millimeters / just over ⅛ inch from the first stitching line, back up to the waist. Use the first row of stitches as a guide to keeping the width even.

topstitched jeans front

Attach the fly shield

10. Remove the basting, or pin, from the zipper.

remove the pin from the zipper

11. Place the fly shield on the zipper and align it with the center front; make sure it covers the edges of the fly facing.

place the fly shield on top of zipper

12. Flip your work, so the front’s facing side is up. Adjust the pins. Change to a zipper foot on your sewing machine and line up your work so you can sew a straight line from the bottom of the shield to the top at the waist.

sew the fly shield to the zipper

13. Attach the fly shield with the zipper pull facing up; move it if necessary when sewing past it.

the zipper attached to the facing and the shield

Stitch the crotch seam

TIPS! Everybody loves a good shortcut. If you want to use one, be sure it’s not the most important part of a garment. The inseam and crotch seam is not the place to apply shortcuts on a pair of jeans.

These seams are what’s holding the whole garment together, and they get a lot of wear and tear during the jean’s lifetime.

If you consider only using the decorative topstitches to keep these seams together, think again, my friend, and find other places on your garment to save some time. 💜

14. Place the left front on the right front, right sides together, align them at the waist and crotch. Mark the right front at the bottom edge of the fly shield.
notch the right front

15. Cut a notch inside of the seam allowance and press it towards the wrong side. 

press the seam allowance towards the back

16. Place the right front on top of the left front, right sides together. Align the pressed seam allowance with the zipper and overcast stitches of the fly shield, pin.

Baste the pieces together 3 millimeters / ⅛  inch in from the edge with a zipper foot.

pin right front to zipper

17. Flip the facing side up and edge stitch the left side of the fly opening. Stitch from the bottom of the fly shield along the zipper up to the waist, making sure the zipper pull is out of the way of the needle.

edge stitch the zipper to the right front

18. Line up the two fronts right sides together, and sew the crotch seam with 1 centimeter / 3/8 inch seam allowance from the bottom to the notch. Press the seam towards the curved topstitches’ side.

pin and sew the crotch seam

19. Flip the right side up and edgestitch the seam in place 3 mm / 1/8 from the edge starting from the bottom. Sew up to the fly stitches, and topstitch back down using the edgestitch as a guide, the same way as you topstitched the fly front.

topstitch the crotch seam

TIPS! Now you can add the classic thread bar at the front of the fly if you want to. But, it’s not necessary because the fly shield is already fastened with the top stitches.

Construct the rest of your garment

There it is, your zipper fly is done!

It’s finally time to sew the rest of your garment.


I admit it; sewing a zipper fly in jeans and pants takes many steps and can indeed be intimidating. But when you’ve done it once or twice, you realize it’s not that bad after all.

Remember, it takes a few times before we learn, so don’t stop trying even if your first attempts get wonky.

With this skill in your toolbox, there’s not much else with sewing that can scare you, am I right?

Practice makes better, and better, and better! So go on and add zipper flys to anything and everything; the sky’s the limit from now on.

Sew great!

signature flaming needle