CRAFTNUMA EDITORIAL · ENGLISH

Plan rectangular fabric pieces before you buy

A fabric estimate starts with the pieces you intend to cut. For a set of identical rectangles, a row layout makes the arithmetic visible and easy to check against a sketch.

Start with the finished rectangle

Suppose you need six pieces measuring 10 by 20 inches at the seam lines. With half an inch on every edge, each cutting rectangle is 11 by 21 inches. Both dimensions gain twice the allowance because a rectangle has two opposing edges in each direction. If your pattern already includes that allowance, use the pattern’s cutting dimensions with zero additional allowance. Adding it again would make the pieces too large.

The rectangular seam allowance tool handles this specific geometry. It cannot offset a curved neckline, calculate a shaped seam or choose how to treat a hem. If one edge needs a different treatment, mark that decision separately and calculate the cutting rectangle yourself.

Count pieces across the usable width

For usable fabric width of 44 inches, four 11-inch pieces fit across. Six pieces therefore require two rows. Two 21-inch rows use 42 inches of length before any extra allowance. The last row has unused positions; that spare area does not reduce the number of rows you must buy.

Our model keeps all pieces in the same orientation. This is useful when grain or a directional print matters. It does not search for a rotated nesting arrangement, mix different piece sizes or match a large print repeat. Draw the rows on paper and confirm the direction before buying or cutting.

Add the allowances you actually need

A 10% extra allowance makes the 42-inch layout 46.2 inches, or about 1.28333333 yards. This is a mathematical estimate, not an instruction to purchase a particular shop increment. If a shop sells in quarter yards, you would need to round that amount up to an available increment after checking your other requirements.

Lengthwise shrinkage is a separate calculation. If your material retains 95% of its original length, a required finished layout length of 42 inches needs 42 ÷ 0.95, or about 44.21052632 inches before shrinkage. Dividing by the retained proportion is different from simply adding 5%. With a further 10% allowance, the estimate becomes approximately 48.63157895 inches.

Check the width assumption

The fabric tool applies the entered shrinkage to length only. Supply a usable width that already allows for widthwise shrinkage, unusable selvedges and any other width restriction. Do not enter the bolt’s nominal width if less of it can be cut. A small width change can remove a whole piece from each row and increase the required length considerably.

Before purchasing, confirm finished versus cutting sizes, the treatment of every edge, grain direction and the supplier’s selling increment. Keep your sketch with the calculation. A tested formula can still give the wrong shopping quantity when the input describes the wrong pieces.