Turn a straight-leg pattern into bell bottoms by extending and widening the pant legs

Bell bottoms start with a regular pant pattern — you do not need a special one. The key is adding length to the inseam and outseam, then widening the leg opening so the fabric flares instead of tapering. Most home sewers add 4 to 6 inches of length and widen the hem opening to 18 to 22 inches around (depending on how dramatic you want the flare). You will grade the width gradually from the knee down so the pants fit normally through the hip and thigh, then flare only below the knee.

The entire process takes about three to four hours once you have your pattern marked and fabric cut. You will work with your existing pattern pieces, redraw the leg seams, cut facing strips for the curved hem, and finish the inside with a facing instead of a standard folded hem. The facing is necessary because the wide, curved opening will bunch if you try to fold and stitch it the traditional way.

Key Takeaways

  • Measure your inseam and add 4 to 6 inches for the bell bottom length, then mark a grading line from the knee to the new hem edge.
  • Widen the hem opening to 18 to 22 inches around by adding width equally to the inseam and outseam below the knee.
  • Grade the width change gradually so the leg stays fitted through the thigh and only flares below the knee.
  • Cut a facing or bias binding for the hem opening because it will be curved and wider than a standard pant leg.
  • Sew the facing to the inside of the hem, then fold and stitch it down to create a clean, professional finish.

Measure and mark the flare on your pattern pieces

Lay your pant pattern pieces flat on a table. Measure the inseam length from the crotch point to the hem edge — this is usually 30 to 32 inches for an adult. Add 4 to 6 inches to this measurement depending on how long you want the bell bottoms to be. Mark this new length on both the front and back pant pieces, measuring down from the crotch point along the inseam.

Next, measure the width of the hem opening on your original pattern. Most straight-leg patterns have a hem opening of 14 to 16 inches around (7 to 8 inches per leg). For bell bottoms, you want 18 to 22 inches around total (9 to 11 inches per leg). Mark the new hem width on your pattern pieces at the bottom edge, adding width equally to both the inseam and outseam.

Now draw a grading line from the knee point down to the new hem edge. This line shows where the leg starts to widen. The knee should stay the same width as your original pattern — all the extra width happens below the knee. Use a ruler or straightedge to draw a smooth, straight line from the knee to each new hem corner. This grading line is your guide for redrawing the seam lines, so make it clear and accurate.

Redraw the inseam and outseam for the flare

Using your grading line as a guide, redraw the inseam and outseam of your pant legs. Start at the knee — this point does not move. From the knee, draw a new line that angles outward to meet your new hem width marks. The line should be smooth and gradual, not sharp or kinked. A French curve or flexible ruler helps here, but a straightedge works if you draw slowly and check your angle as you go.

Redraw both the inseam and outseam on the front pant piece, then repeat on the back piece. The back piece usually flares slightly more than the front to account for the way the leg hangs when you walk. Add about 0.5 inches more width to the back outseam than the front outseam if you want a traditional bell bottom shape. Check that your new seam lines are symmetrical — measure from the center line of the pant leg to the new inseam and outseam at the hem. Both sides should be equal distance from center. If one side is wider than the other, the pants will twist when you wear them.

Cut your fabric and prepare the hem facing

Cut your pant pieces from your fabric using the redrawn pattern. Cut two front pieces and two back pieces, plus any waistband or pocket pieces your pattern calls for. Lay out your pieces on the fabric grain line just as your original pattern shows — the grain line does not change, only the shape of the leg. Use sharp fabric scissors or a rotary cutter to cut clean, straight edges along your new seam lines.

The hem opening on bell bottoms is wider and more curved than a straight-leg pant, so a standard hem facing will not fit smoothly. Cut a facing strip from your fashion fabric or lining fabric. The facing should be 2 to 2.5 inches wide and long enough to go around the entire hem opening — measure the hem opening perimeter and add 1 inch for seam allowance overlap. If your hem opening is 20 inches around, cut a facing strip that is 2.5 inches wide and 21 inches long.

Fold the facing strip in half lengthwise with wrong sides together, then press it flat with an iron. This creates a 1.25-inch-wide facing that is straightforward to attach and fold to the inside. If you prefer a thinner facing, fold it to 1 inch wide instead. The fold makes the facing more stable and prevents raw edges from showing on the inside of the finished pants.

Attach the facing to the hem opening

Sew the two pant legs together at the inseam and outseam using a straight stitch and a 0.5-inch seam allowance. Press the seams open with an iron. Try on the pants to check the length and fit — you should be able to stand on the hem edge without the fabric bunching. If the length is wrong, adjust now before attaching the facing. This is your final note to make changes without unpicking the facing later.

Pin the facing strip to the hem opening with right sides together, matching the raw edges. The facing should overlap itself by 1 inch where the ends meet — overlap the ends and pin them together. Sew the facing to the hem opening using a 0.5-inch seam allowance and a straight stitch. Use a walking foot if your machine has one, because the curved hem opening can shift as you sew. Sew slowly and let the machine feed the fabric — do not pull or push.

Trim the seam allowance to 0.25 inches and clip into the curve every 1 inch so the facing will lie flat when you fold it to the inside. Be careful not to clip through the stitching line. Press the seam allowance toward the facing using an iron set to medium heat.

Fold and stitch the facing to finish the hem

Fold the facing to the inside of the pant leg along the stitching line you just made. Press the fold flat with an iron. The facing should lie smoothly against the inside of the leg with no puckers or wrinkles. If the facing pulls or bunches, you may have cut it too short — unpick it and recut a longer strip. Take your time with this step because a smooth, flat facing is what makes the finished pants look professional.

Stitch the facing down by sewing close to the fold edge on the inside of the pant leg. Use a straight stitch and match your thread to the facing fabric. Sew all the way around the hem opening. This stitching holds the facing in place and creates a clean, professional finish on the inside. Alternatively, you can hand-stitch the facing using a slip stitch if you want an invisible seam. Fold the raw edge of the facing under 0.25 inches and pin it to the inside of the pant leg. Use a needle and thread that matches the facing, and sew with small, tight stitches that catch only one or two threads of the pant fabric.

Press and try on your finished bell bottoms

Press the entire pant leg with an iron set to the temperature appropriate for your fabric. Press the hem flat, then press the inseam and outseam from the inside so they lie smoothly. Press the waistband and any cuffs or hems at the top of the pants. Use a pressing ham or sleeve board to help shape the curved hem opening as you press.

Try on the pants and check the fit. The bell bottoms should sit at your natural waist or hip, fit smoothly through the thigh and knee, and flare evenly below the knee. The hem should break slightly on the top of your shoe — about 0.5 inches of fabric should touch the shoe when you stand. If the flare is too wide or too narrow, or if the hem length is wrong, you can unpick the facing and adjust the leg width or length before reattaching it. Walk around in them for a few minutes to make sure the seams feel comfortable and the legs do not twist.

Frequently Asked Questions

How much should bell bottoms flare?

A modest flare is 18 to 20 inches around the hem opening, which looks balanced on most body types. A dramatic flare is 20 to 24 inches around. Start with 20 inches if you are unsure — you can always make them wider by unpicking the facing and adding more width to the inseam and outseam.

Can I add bell bottoms to pants I already own?

Yes, but it is more work than starting with a pattern. You will need to unpick the inseam and outseam from the knee down, then add fabric panels to widen the legs. This works best if your original pants are made from a fabric that matches something you can find — matching the color and weight is difficult after the fact.

What if my bell bottoms twist or spiral when I walk?

Twisting usually means the inseam and outseam are not symmetrical — one side is wider than the other. Unpick the facing and measure the width on both sides of each leg at the hem. Both sides should be equal distance from the center seam. If they are not, redraw the seam line and reattach the facing.

Do I need a special presser foot for sewing the curved hem?

A walking foot helps keep the fabric from shifting on curved seams, but it is not required. You can sew the facing on with a standard presser foot if you sew slowly and use your hands to guide the fabric gently. Pinning every 1 inch also helps prevent shifting.

Can I use a regular hem instead of a facing?

A facing is easier and looks cleaner on a wide, curved hem opening. A regular folded hem will bunch and pucker because the curve is too tight. If you want a folded hem, you would need to add much less width to the bell bottom — only 2 to 3 inches total — so the curve is gentler.