How to calculate fabric yardage for rectangular pieces

Fabric is sold by length, but every piece consumes both width and length. Two projects with the same total area can need different yardage because their rectangles fit across the bolt differently.

Start with four facts

For each rectangular piece, record the finished width, finished height, and quantity. Then measure the usable fabric width: the full bolt width minus any selvage or edge you cannot cut. Keep every measurement in one unit until the end.

The basic row method

1. Add the required allowance to all relevant edges of the finished piece.
2. Divide usable fabric width by cut-piece width and round down. That is the number that fit across one row.
3. Divide quantity by pieces per row and round up. That is the number of rows.
4. Multiply rows by cut-piece height. This gives the base layout length.

A worked example

Suppose you need six panels with a cut size of 40 × 50 cm and the usable fabric width is 150 cm. Three panels fit across because floor(150 ÷ 40) = 3. Six panels need two rows, so the base layout length is 2 × 50 = 100 cm.

If the store sells in 10 cm increments and you want a 10% project reserve, the planning sequence is:

100 cm layout
+ 10 cm reserve
= 110 cm
→ 110 cm purchase length

Why area alone gives the wrong answer

The six panels contain 12,000 cm² of fabric. Dividing that by a 150 cm width suggests only 80 cm of length. But the 30 cm remainder beside each row cannot fit another 40 cm panel. A cutting layout exposes that geometric waste; a square-area calculation hides it.

When to try rotation

A solid, non-directional fabric may allow a 90-degree rotation that reduces length. Do not rotate when the grain, nap, one-way print, stretch direction, or pattern matching requires a fixed orientation. A shorter mathematical layout is not useful if the finished pieces face the wrong way.

Turn layout length into purchase length

Keep the additions visible: base layout, pattern-repeat addition, reserve, and store rounding. This makes the answer easy to check and prevents the same risk from being counted twice. The planner reports each component separately.

Final check before ordering

• Confirm the listed width is usable width, not only nominal bolt width.
• Confirm every quantity and finished dimension.
• Add the actual seam or hem construction your project needs.
• Disable rotation when direction or grain matters.
• Account for pattern repeat before applying a general reserve.
• Round up to the increment your shop will actually sell.