The Basic Process for Attaching a Collar
A shirt collar is sewn in three main stages: you interface the collar pieces for structure, sew the two collar halves together, and then attach the finished collar to the neckline. The whole process takes about 45 minutes once you have cut your pieces. Most home sewers find collars easier than they expect because each stage is straightforward — the key is taking time to press as you go, which makes the final steps fit together cleanly.
The collar you see on a finished shirt is actually two layers of fabric with interfacing sandwiched between them. This sandwich gives the collar its shape and prevents it from flopping. You will work with three pieces: the top collar (the visible outside), the under collar (the inside facing), and interfacing, which is a stiff fabric that bonds to one side of your under collar with heat from an iron.
Key Takeaways
- Interface the under collar piece first by fusing interfacing to the wrong side with a hot iron, following the interfacing package instructions for heat and pressure.
- Sew the top and under collar pieces together with a 5/8-inch seam allowance, leaving the neckline edge open, then trim seams and turn the collar right-side out.
- Press the collar flat after turning, rolling the seam slightly to the under collar side so it does not show on the finished garment.
- Pin the collar to the neckline with the under collar facing the garment body, then sew it in place with a 5/8-inch seam, and fold the under collar seam allowance down to encase the raw edges.
- A topstitch — a visible line of stitching about 1/4 inch from the fold — holds the under collar in place and gives the collar a professional finish.
Preparing the Collar Pieces with Interfacing
Start by cutting two collar pieces from your fabric and one piece of interfacing. The interfacing should be the same size as your under collar piece. Check your pattern to see whether it calls for woven or knit interfacing — woven is stiffer and works well for crisp collars, while knit is softer and suits casual shirts.
Place the interfacing on the wrong side of the under collar piece, with the bumpy or adhesive side facing down. Set your iron to the heat level printed on the interfacing package — usually medium to medium-high. Press down firmly for 10 to 15 seconds, moving the iron in small overlapping circles. Do not slide the iron back and forth, as that can shift the interfacing. Let the piece cool for a minute before picking it up. The interfacing should feel bonded to the fabric and not peel away at the edges.
Sewing the Two Collar Halves Together
Place the top collar and under collar pieces with right sides together — the pretty sides facing each other. Pin along the three outer edges (the two short ends and the long outer curve), leaving the neckline edge unpinned. This unpinned edge is where the collar will attach to the shirt.
Sew around the three pinned edges using a 5/8-inch seam allowance, which is the standard for most garment sewing. Backstitch at the start and end. Sew slowly around the curves so your stitches stay even. Once you reach the other neckline corner, backstitch and remove the collar from the machine.
Trim the seam allowance down to 1/4 inch, cutting close to your stitching line but not into it. At the two corners, cut diagonally across the corner point — this removes bulk so the corner turns sharp instead of lumpy. Clip small notches into the seam allowance along the outer curve, cutting perpendicular to the seam line about every 1/2 inch. These clips let the fabric curve smoothly when you turn it.
Turn the collar right-side out through the open neckline edge. Use a point turner or the blunt end of a chopstick to gently push the corners out from the inside. Press the collar flat with your iron, paying special attention to the edges. As you press, roll the seam slightly toward the under collar side — about 1/8 inch — so the seam sits just inside the edge and does not show on the top collar. This rolling is what makes a collar look professionally finished.
Attaching the Collar to the Neckline
Before you attach the collar, prepare your neckline. If your pattern calls for a facing or bias binding, sew that to the neckline first and press it to the inside. If you are working with a straightforward neckline, you can attach the collar directly.
Pin the collar to the neckline with the under collar facing the garment body and the top collar facing outward. The raw neckline edges of the collar should line up with the raw neckline edge of the shirt. Pin at the center back, center front, and shoulder seams first, then add pins every 2 inches around the curve. The collar should sit flat against the neckline with no puckers or gaps.
Sew the collar to the neckline using a 5/8-inch seam allowance. Sew slowly and stop frequently to check that the fabric is feeding evenly. Once you have sewn all the way around, backstitch and remove the garment from the machine.
Finishing the Neckline Seam
Trim the seam allowance to 1/4 inch. Fold the under collar seam allowance down and to the inside of the garment, encasing the raw edges of the neckline seam. Pin it in place so it lies flat and covers the stitching line you just made. Hand-sew this fold down using a ladder stitch — a nearly invisible stitch that catches one thread of the fold, then one thread of the garment, alternating back and forth. Use thread that matches your fabric and take small stitches about 1/8 inch long.
If hand-sewing feels tedious, you can topstitch instead. A topstitch is a visible line of stitching sewn from the outside of the garment, about 1/4 inch from the fold where the collar meets the neckline. This holds the under collar in place and is a common finish on casual and work shirts. Use thread that matches your top collar and sew slowly so the line stays straight.
Common Mistakes and How to Avoid Them
The most common mistake is skipping the interfacing or using interfacing that is too soft. Without it, the collar will flop and look homemade. If your pattern does not specify interfacing weight, choose a medium-weight woven interfacing — it works for most shirt collars.
Another frequent problem is not pressing enough. Pressing after each step — after fusing the interfacing, after sewing the collar halves, and after attaching to the neckline — makes every step easier and the finished collar look sharper. A collar that has not been pressed looks wrinkled even when it is not.
Uneven seam allowances around the neckline cause the collar to sit crooked. Pin carefully and sew slowly, stopping every few inches to make sure the fabric is feeding straight. If you notice the seam is wandering, stop, backstitch, and start again from a pinned point.
Forgetting to clip the curves and corners before turning means your collar will have lumpy, puckered edges. Take the time to trim and clip — it takes two minutes and makes a visible difference.
Pressing and Final Details
Once the collar is fully attached and the under collar is secured, give the entire neckline a final press. Use a pressing ham or rolled towel under the neckline curve so you can press the seam without flattening the collar. Press from the inside first, then flip and press from the outside. This final press sets all your stitches and gives the collar its finished shape.
If you are making a button-up shirt, you may need to sew buttons at the collar points or add collar stays — thin strips of plastic or bone that slide into pockets on the underside of the collar to keep it crisp. These are optional but common on dress shirts. Collar stays are usually included with your pattern if they are needed.
Frequently Asked Questions
What is the difference between a top collar and an under collar?
The top collar is the piece you see on the outside of the finished garment. The under collar is the inside piece. Both are sewn together with interfacing between them, but the under collar is the one that gets fused to the interfacing. This two-layer sandwich gives the collar structure and prevents it from sagging.
Can I sew a collar without interfacing?
You can, but the collar will be limp and will not hold its shape. Interfacing is inexpensive and takes five minutes to fuse. It is worth doing — it is the difference between a collar that looks handmade and one that looks store-bought.
Why does my collar pucker where it meets the neckline?
Puckering usually means the seam allowance is too wide or the fabric was stretched as you sewed. Trim your seam allowance to 1/4 inch after sewing, and sew slowly around curves so the presser foot does not pull the fabric. If puckering happens again, you may need to clip more notches into the curve before attaching the collar.
Do I have to hand-sew the under collar down, or can I machine-sew it?
You can machine-sew it with a topstitch, which is faster and looks professional on casual shirts. Hand-sewing with a ladder stitch is nearly invisible and is better for dress shirts where you want the neckline to look seamless. Choose whichever matches the style of your garment.
What if my collar does not lie flat against the neckline?
Check that you pinned it evenly all the way around and that the neckline seam allowance is trimmed to 1/4 inch. If the collar still gaps, the neckline may be slightly too large or the collar slightly too small — this is usually a pattern or cutting issue rather than a sewing one. For future projects, measure your neckline and collar before sewing to catch size mismatches early.