The Basic Seam: Where the Needle Goes

A seam is straightforward two pieces of cloth held together by thread running through both layers. To sew cloth together, you align the edges you want joined, hold them in place, and run thread through both pieces in a straight line. The thread locks the layers together so they do not separate when pulled or washed.

The distance from the edge of the cloth to your line of stitches is called the seam allowance. Most garments use a half-inch seam allowance, though some patterns call for a quarter-inch. Thicker fabrics like denim or canvas often use a half-inch or wider allowance. Thinner fabrics like silk or cotton voile may use a quarter-inch to avoid bulk.

You can sew by hand with a needle and thread, or by machine. Hand sewing is slower but requires no equipment beyond needle, thread, and scissors. Machine sewing is faster and produces stronger seams, but requires access to a sewing machine.

Key Takeaways

  • A seam allowance is the space between the cloth edge and your stitching line, usually a half-inch for most projects.
  • Hand sewing uses a running stitch or backstitch, with the backstitch being stronger for seams that will bear weight or stress.
  • Machine sewing requires you to align cloth edges under the presser foot, set the stitch length, and guide the fabric straight.
  • Pinning or basting cloth before sewing keeps the layers from shifting and produces a straighter seam.
  • Pressing seams flat with an iron after sewing makes them lie smooth and look finished.

Hand Sewing: The Running Stitch and Backstitch

The running stitch is the simplest hand stitch. Thread your needle, knot the end, and push the needle through both layers of cloth from the back. Bring it back out a quarter-inch forward. Push it back in and out again, repeating in a line. The stitches should be small and even. This stitch is fast but not very strong, so use it for temporary seams or light fabrics that will not bear much stress.

The backstitch is stronger and better for seams that need to hold. Push the needle through both layers from the back, then bring it out a quarter-inch ahead. Push the needle back into the hole where the last stitch ended, then bring it out another quarter-inch ahead. Each new stitch overlaps the previous one, creating a solid line. Backstitches take longer than running stitches but will not come apart easily.

To start either stitch, push the needle through the cloth from back to front, leaving a short tail on the back side. Make a small knot at the end of the thread before you begin, or take three or four tiny stitches in the same spot to anchor the thread. To finish, take three or four stitches in the same spot again, then knot the thread on the back side and trim the excess.

Machine Sewing: Setup and Straight Seams

Thread the machine according to your machine's manual — the thread path varies by model. Wind a bobbin (the small spool that holds thread underneath) and insert it into the bobbin case. Set the stitch length to 2.5 millimeters, which is standard for most fabrics. Thicker fabrics may need a longer stitch; thinner or delicate fabrics may need a shorter one.

Place your two pieces of cloth under the presser foot (the metal piece that holds fabric down) with the right sides facing each other — the sides you want to show on the finished garment should be touching. Align the edge of the cloth with the seam allowance guide on the machine bed, usually marked with lines. Lower the presser foot and begin sewing by pressing the foot pedal or pressing the start button, depending on your machine.

Guide the cloth straight by holding it gently on both sides of the presser foot, but do not pull or push — let the machine feed the cloth. Keep your eyes on the seam allowance line, not on the needle. When you reach the end, stop with the needle down, raise the presser foot, and pull the cloth toward you to cut the thread. Most machines cut the thread automatically; if yours does not, use scissors.

Pinning and Basting to Keep Cloth Aligned

Pinning holds two pieces of cloth together before you sew, so they do not shift while you work. Place pins perpendicular to the seam line (at right angles to the direction you will sew) every two to three inches. The pin heads should stick out on one side so you can remove them easily. When you reach a pin while sewing by machine, stop, raise the presser foot, remove the pin, lower the foot, and continue.

Basting is temporary stitching that holds cloth in place before the final seam. Use a long stitch length (4 to 5 millimeters on a machine, or large stitches by hand) and sew along the seam line. Basting is useful when cloth is slippery, when pieces are cut at angles, or when you are sewing a long seam and want to check the fit before committing to the final stitch. Remove basting stitches after you sew the final seam by pulling the thread gently.

Pressing Seams Flat

After sewing, press the seam with an iron to flatten it and make it look finished. Set the iron to the temperature appropriate for your fabric — check the fabric care label or test on a scrap first. Place the sewn pieces on an ironing board with the seam running lengthwise. Press the iron down firmly along the seam line, moving it slowly from one end to the other. Do not slide the iron back and forth like you are ironing a shirt; press and lift.

Most seams are pressed to one side, usually toward the darker fabric or the back of the garment. Some seams, especially in quilting, are pressed open — the two seam allowances are folded away from each other and pressed flat. Pressing seams open reduces bulk in thick fabrics and is common in tailored garments.

Seam Finishes for Cloth That Frays

Natural fabrics like cotton, linen, and wool fray at the edges when washed or worn. If you want a finished look, trim the raw edges of the seam allowance and cover them with a finish. The simplest finish is a zigzag stitch — set your machine to zigzag and sew along the raw edge of each seam allowance. The zigzag thread locks the fibers so they do not unravel.

A French seam encloses the raw edges inside the seam itself. Sew the first seam with wrong sides together (raw edges facing out), then trim the seam allowance to a quarter-inch. Fold the cloth so right sides are now together and sew again a quarter-inch from the fold. The raw edges are now hidden inside. French seams are strong and neat but use more fabric and are slower to sew.

Synthetic fabrics like polyester do not fray as much as natural fibers, so a straightforward seam without a finish is often acceptable. Test a scrap of your fabric by washing it to see whether fraying is a problem for your project.

Common Mistakes and How to Avoid Them

Uneven seam allowance is the most common mistake. The seam wanders instead of staying parallel to the edge. To avoid this, use the seam allowance guide on your machine and keep your eyes on the guide line, not on the needle. When hand sewing, mark the seam line lightly with a pencil or tailor's chalk before you begin.

Puckered seams happen when cloth is pulled while sewing, stretching one layer more than the other. Let the machine feed the cloth — do not pull. If you are sewing stretchy fabric like knit or jersey, use a ballpoint needle and a stretch stitch setting if your machine has one. Puckering can also happen if the thread tension is too tight; check your machine manual for how to adjust it.

Skipped stitches occur when the needle does not catch the thread properly. This usually means the needle is bent, dull, or inserted backward. Replace the needle — they are inexpensive and wear out with use. Make sure the needle is inserted all the way into the needle clamp and facing the correct direction for your machine.

Frequently Asked Questions

What size needle should I use?

Needle size depends on fabric weight. Use a size 60/8 or 70/10 needle for lightweight fabrics like silk or cotton voile. Use 80/12 or 90/14 for medium-weight fabrics like cotton or linen. Use 100/16 or 110/18 for heavy fabrics like denim or canvas. Hand sewing needles come in sizes 1 to 12, with higher numbers being smaller; use a size 7 or 8 for most cloth.

How tight should I pull the thread when hand sewing?

Pull the thread snug enough that the cloth layers do not shift, but not so tight that the cloth puckers or the thread breaks. The cloth should lie flat after each stitch. If you are new to hand sewing, practice on scrap cloth first to get a feel for the right tension.

Can I sew different types of fabric together in one seam?

Yes, but the seam will be as strong as the weaker fabric. If you are sewing a lightweight fabric to a heavy one, the lightweight fabric may tear at the seam under stress. Use a needle size appropriate for the lighter fabric and reduce the stitch length slightly to distribute the stress over more stitches.

What thread should I use?

All-purpose polyester thread works for most fabrics and projects. Cotton thread is traditional and works well on natural fabrics. Match the thread color to the fabric or use a neutral color like gray or tan. Thicker thread is visible and decorative; thinner thread is less noticeable. For most seams, use standard all-purpose thread in a matching or neutral color.

Do I need to wash cloth before sewing?

Wash natural fabrics like cotton and linen before cutting and sewing, because they shrink when washed. Wash in warm water and dry as you plan to care for the finished garment. Synthetic fabrics like polyester do not shrink much, so washing is optional. Always test a scrap of your fabric first to see how much it shrinks.