A seam is where two pieces of fabric join together, held by a line of stitches

A seam is straightforward two pieces of fabric sewn together with thread. The stitches lock the fabric pieces in place so they don't separate when you wash, wear, or stretch the garment. Whether you sew by hand or machine, the basic idea is the same: thread passes through both layers of fabric in a repeating pattern that creates a strong line.

Most seams in clothing and home items are sewn 5/8 inch from the edge of the fabric (called the seam allowance). This distance gives you room to trim, finish, or adjust the seam later if needed. The actual distance varies depending on the pattern you're following, but 5/8 inch is the standard in most sewing.

You can sew a seam by hand with a needle and thread, or use a sewing machine. Hand sewing is slower but requires no equipment beyond needle, thread, and scissors. Machine sewing is faster and creates a stronger seam for items that will get heavy use.

Key Takeaways

  • A seam holds two pieces of fabric together using a line of stitches, and most seams are sewn 5/8 inch from the fabric edge.
  • Hand sewing uses a needle and thread with straightforward stitches like the running stitch or backstitch, and works well for repairs and light fabrics.
  • Machine sewing is faster and stronger, and requires threading the machine, setting the stitch length, and guiding the fabric under the presser foot.
  • Pinning or marking your seam line before you start keeps both pieces of fabric aligned and prevents crooked stitches.
  • After sewing, you can finish the raw edges with pinking shears, a zigzag stitch, or binding to prevent fraying.

Hand Sewing a Seam: The Running Stitch

The running stitch is the simplest hand seam and works for light repairs, hems, and fabrics that won't get stretched. Thread a needle, tie a knot at the end of your thread, and push the needle through both layers of fabric from the back. Pull the thread until the knot stops it. Then push the needle back through both layers about 1/8 inch forward, creating a small stitch on top and a longer stitch underneath. Repeat this motion along your seam line, keeping your stitches as even as possible.

The running stitch is fast but not very strong because each stitch is short and the thread can pull through fabric easily. Use it for seams that won't bear weight or stress, such as attaching a patch, closing a decorative seam, or hemming a lightweight scarf.

Hand Sewing a Seam: The Backstitch

The backstitch is stronger than the running stitch and is the best choice for hand-sewn seams that need to hold. Start the same way—thread your needle, tie a knot, and push through both layers. Bring the needle up through the fabric about 1/8 inch ahead of where you started. Then push the needle back down through the hole where your thread came out, creating an overlap. Bring the needle back up another 1/8 inch ahead and repeat. Each stitch overlaps the previous one, which locks the thread in place.

The backstitch takes longer than the running stitch but creates a seam that won't unravel if one stitch breaks. Use it for seams that will be washed, worn, or stretched, such as closing a pillow, repairing a torn seam in a garment, or sewing a bag.

Machine Sewing a Seam: Setup and Threading

Before you sew, your machine must be threaded correctly. Thread the top of the machine by following the path marked on your machine (usually a series of guides and hooks that lead down to the needle). The thread should sit in the tension discs—two metal plates that grip the thread and control how tight it is. Then thread the bobbin (the small spool underneath) by inserting it into the bobbin case and pulling the thread through the slot. Most machines have a diagram on the side showing the exact path.

Once threaded, set your stitch length. Most machines have a dial or digital display; a setting of 2.5 to 3 millimeters is standard for most fabrics. Shorter stitches (1.5 to 2 mm) create a tighter seam for stretchy or delicate fabrics. Longer stitches (3.5 to 4 mm) work for heavy fabrics or basting (temporary stitching). Check your machine's manual for the exact settings, as they vary by model.

Machine Sewing a Seam: Stitching and Guiding Fabric

Place your two fabric pieces right sides together (the pretty sides facing each other) and align them under the presser foot—the metal piece that holds the fabric down. Lower the presser foot by moving the lever behind it. Position the fabric so the edge aligns with the 5/8-inch mark on the throat plate (the metal plate with measurement lines). This keeps your seam at the correct distance from the edge.

Hold the thread tails loosely in your hand and press the foot pedal to start sewing. The machine will pull the fabric forward automatically, so guide it gently with your hands rather than pushing. Keep your eye on the edge of the fabric and the measurement line to stay straight. When you reach the end, stop the machine, raise the presser foot, and trim the thread tails with scissors.

Backstitch at the start and end of your seam to lock the stitches in place. Most machines have a reverse button or lever; press it and sew backward about 1/2 inch, then forward again to the end. This prevents the seam from unraveling when the garment is washed or worn.

Marking and Pinning Your Seam Line

Before you sew, mark or pin your seam line so both pieces of fabric stay aligned. For hand sewing, use a fabric pencil or chalk to draw a light line 5/8 inch from the edge. For machine sewing, you can rely on the measurement marks on the throat plate, but pinning helps keep the fabric from shifting.

Place pins perpendicular to the seam line (at right angles) every 3 to 4 inches. This holds the two layers together without bunching. When you reach a pin while sewing by machine, stop, remove the pin, and continue. Never sew over a pin—it can break the needle or damage the machine. For hand sewing, you can leave the pins in place as you work, or remove them as you go.

Finishing the Raw Edges

After you sew a seam, the cut edges of the fabric are exposed and will fray over time, especially after washing. Finishing these edges makes your seam stronger and more professional-looking. The simplest method is to trim the seam allowance with pinking shears (scissors with zigzag blades) about 1/4 inch from the stitches. The zigzag edge slows fraying.

For a more durable finish, use a zigzag stitch on your machine. Sew a zigzag line along each raw edge of the seam allowance. This locks the fibers and prevents unraveling even after many washes. Some machines have a serger (a specialized machine that cuts and finishes edges in one step), but a regular machine's zigzag stitch works well for most projects.

For very delicate or stretchy fabrics, you can bind the edges with bias tape—a narrow strip of fabric folded and sewn over the raw edge. This method takes more time but creates a neat, professional finish that won't fray at all.

Frequently Asked Questions

What's the difference between sewing right sides together and wrong sides together?

Right sides together means the pretty, finished sides of the fabric face each other while you sew. This hides the stitches inside the finished garment. Wrong sides together puts the back sides facing each other, leaving stitches visible on the outside. Always sew right sides together unless the pattern specifically says otherwise.

Can I sew a seam without pinning?

Yes, especially with a machine and a marked seam line. Pinning takes extra time but prevents the fabric from shifting, which is helpful when you're learning or working with slippery fabrics like silk or satin. For hand sewing, pinning is less critical because you can adjust as you go.

How do I fix a crooked seam?

If the seam is only slightly off, you can live with it—small imperfections don't affect how the garment wears. If it's very crooked and visible, you can carefully cut the stitches with a seam ripper (a small tool with a curved blade), pull the fabric apart, and sew again. This works better on hand-sewn seams than machine seams.

What thread should I use?

All-purpose polyester thread works for most fabrics and both hand and machine sewing. For delicate fabrics like silk, use silk thread. For stretchy fabrics like knits, use elastic or stretch thread. Match the thread color to your fabric, or use a neutral color like gray or beige if you're unsure.

How tight should the tension be on my machine?

Correct tension means the top and bottom threads lock together in the middle of the fabric layers, creating even stitches on both sides. If the top thread is too loose, the bottom thread will show on top. If it's too tight, the fabric will pucker. Most machines come set to the correct tension, but check your manual if stitches look uneven.