Planning a cutting layout and buying the right yardage
How pieces tile across a bolt, why rows round up, when to cut along the length, and how to add seam allowance and shrinkage before you buy.
How pieces tile across the bolt
Fabric comes off a bolt at a fixed usable width, and cutting is most efficient when you fill that width before moving down the length. The tool divides the fabric width by your piece width and rounds down to find how many pieces sit side by side in a row. Ten 12 inch pieces on 44 inch cotton fit 3 across, because 44 divided by 12 is 3.66 and you cannot cut a fraction of a piece. The leftover strip on the side is unavoidable waste unless you resize the piece or the cut plan.
Rows, total length and yardage
Once the pieces per row is set, the number of rows is the quantity divided by that figure, rounded up, since a partial row still consumes a full piece length. Ten pieces at 3 per row need 4 rows. The total fabric length is the rows times the piece length, so 4 rows of 15 inch pieces is 60 inches. Dividing by 36 gives 1.6667 yards. Switch the unit toggle to centimeters and the same layout reports the length in centimeters with a meters figure instead.
When a piece is wider than the fabric
Sometimes a single piece is wider than the usable bolt, like a 50 inch panel on 44 inch cotton. It cannot be tiled across the width, so the tool drops to one piece per row and flags that the piece must be cut along the length of the bolt instead. Two such panels then take two rows and 60 inches of fabric. When you see that amber note, plan to run the piece down the yardage, and remember that directional prints and nap may limit how you can rotate it.
Add seam allowance and a shrinkage margin
The calculator lays out the exact finished rectangles you type in, with no padding. Before you enter a size, add your seam allowance to both the width and the length of each piece, commonly a quarter inch per side for quilting and more for apparel. Then buy a little beyond the yardage the tool returns to cover pre wash shrinkage, squaring up a crooked cut end, and matching a repeating pattern. A spare quarter to half yard is cheap insurance against coming up short mid project.