Strip Piecing Calculator

How strip piecing math works

Strip piecing sews long strips together, then crosscuts the set into ready-made units. You cut each strip at its finished width plus two seam allowances — ¼″ on each long edge.

A worked example: 8 strips finishing 2″ wide

With the standard ¼″ seam allowance and 40″ of usable width — the calculator's defaults:

The seam allowance is already in the 2½″ — that is why a jelly roll strip is 2½″ wide and finishes at 2″. Cutting at 2″ because that is the number in the pattern is the single most common strip-piecing error, and it shrinks every unit in the quilt.

Jelly rolls are pre-cut strips

A jelly roll is forty 2½″ strips — already cut, so the math is done for you, and they finish at exactly 2″. If you're designing your own, the jelly-roll quilt math guide shows how many strips a quilt needs, and strip-pieced block yardage covers converting a block design into strips.

Common mistakes

Cutting at the finished width. Add both seam allowances; the calculator does it for you. Letting the strip set bow. Sewing every seam in the same direction curves a long strip set like a banana, and every crosscut segment inherits the curve. Alternate your sewing direction with each strip you add. Crosscutting without re-squaring. After pressing, trim one end square before you start cutting segments, and re-square every few cuts. Pressing along the strip. Press straight down; dragging the iron stretches a 40″ strip noticeably.

Press to the side or open

Pressing to one side, usually toward the darker strip, lets seams nest — butt snugly together — when you join segments, which is what makes points meet. Pressing open gives a flatter block with less bulk but nothing to nest against. Alternate direction row to row if you are nesting. Strip piecing basics works through both.

Common questions

How many segments will one strip give me?

Usable width divided by your segment width. A 40″ strip crosscut at 2½″ yields 16 segments, and the calculator works this out when you enter a subcut size.

Does this work for fat quarters?

The strip lengths change — a fat quarter is about 18″ × 21″, so strips are half the length of a WOF cut. Fat quarters vs. yardage covers the conversion.

What if my pattern uses a scant ¼″ seam?

Keep the cut width the same and sew a hair inside the ¼″ line. The cut math does not change; a scant seam is a correction for the thread and the fold taking up space.