Show the math
The calculator lays the pieces out in a single uniform grid, once as entered and once turned 90°, and reports the better of the two.
- Pieces along a side
- ⌊(sheet side − 2 × edge + spacing) ÷ (piece side + spacing)⌋
- Normal layout
- along(sheet width, piece width) × along(sheet height, piece height)
- Rotated layout
- along(sheet width, piece height) × along(sheet height, piece width)
- Pieces per sheet
- the larger of normal and rotated
- Offcut
- 1 − pieces × piece width × piece height ÷ (sheet width × sheet height)
- Material per piece
- sheet cost ÷ pieces per sheet ÷ (1 − extra waste)
Why add one spacing gap? Five pieces in a row need only four gaps between them. Adding a gap to the usable length and dividing by piece-plus-gap counts exactly that: n pieces and n − 1 gaps.
Worked examples
2 × 3-inch keychains on a 12 × 20-inch sheet
Spacing 0.125", edge margin 0.25". Across the 12" side: ⌊(12 − 0.5 + 0.125) ÷ 2.125⌋ = ⌊5.47⌋ = 5. Down the 20" side: ⌊(20 − 0.5 + 0.125) ÷ 3.125⌋ = ⌊6.28⌋ = 6. That's 30 pieces. Rotated, 3 across and 9 down make 27. The 30 pieces cover 30 × 6 = 180 of the sheet's 240 square inches, so the offcut is 25%. At $9.80 a sheet and 8% extra waste, material comes to $9.80 ÷ 30 ÷ 0.92 = $0.355 per piece.
3.5-inch square ornaments on the same sheet
A square piece gives the same count both ways: 3 across, 5 down, 15 pieces. They cover 15 × 12.25 = 183.75 square inches, an offcut of 23.4%. At $3.50 for a birch sheet and 10% waste, that's $0.259 per ornament.
Metric: 50 × 30 mm tags on a 600 × 400 mm sheet
Spacing 3 mm, edge 5 mm. Normal: ⌊593 ÷ 53⌋ = 11 across and ⌊393 ÷ 33⌋ = 11 down, 121 pieces. Rotated: ⌊593 ÷ 33⌋ = 17 across and ⌊393 ÷ 53⌋ = 7 down, 119. The normal layout wins by two, with a 24.4% offcut. Nothing about the formula changes with the unit.
Offcut is already in your material cost
Dividing the sheet cost by the number of pieces spreads the whole sheet, offcut included, over the pieces you sell. That's why the 25% offcut on the keychain sheet doesn't need its own line in a price. The extra-waste percentage is for losses on top: test cuts, a flawed sheet, a scratched piece. Count the offcut once, not twice. If you sell small items cut from the leftover strips, you can lower the waste figure to reflect that.
When you can beat the grid by hand
- Mixed orientation. If the strip left along one side is wider than the piece's other dimension, an extra row of rotated pieces may fit. The calculator counts one uniform grid, which is the number you can repeat sheet after sheet.
- Shared cut lines. Rectangles that touch can share a single cut. Set spacing to 0 to count that layout.
- Irregular shapes. Enter the bounding box (the smallest rectangle around the shape). Nesting software can interlock irregular parts more tightly; treat the grid count as the safe figure to price on.