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Parent sheet, press sheet, job
Paper arrives in parent sheet sizes such as 70 × 100 or 64 × 90 cm. The press takes either the whole sheet or a cut-down part of it: a 70 × 100 sheet gives two 50 × 70 or four 35 × 50 sheets.
So the calculation has two layers: how many press sheets come out of the parent sheet, and how many pieces come out of each press sheet. Getting the first right and the second wrong — or the other way round — costs paper either way.
Subtract what the press takes first
Not all of the press sheet can carry print. On a sheet-fed press the grippers hold one edge (commonly around 10 mm), the tail edge needs a margin, and the sides need a little too. The layout is calculated on what's left, not on the full sheet.
Each piece is counted with its bleed. An A5 flyer (148 × 210 mm) with 3 mm bleed on every side takes 154 × 216 mm on the sheet.
Try both ways round
Take a 50 × 70 press sheet with a usable area of about 490 × 690 mm after the margins, and the 154 × 216 mm flyer:
- Upright: 490 ÷ 154 = 3 across, 690 ÷ 216 = 3 down — 9 flyers.
- Turned: 490 ÷ 216 = 2 across, 690 ÷ 154 = 4 down — 8 flyers.
- The same sheet, one flyer more per sheet just by turning the piece. Over 5,000 flyers that's about 70 sheets.
The sheet with the most pieces isn't always the cheapest
Count per sheet is the wrong yardstick; paper per piece is the right one. Divide the sheet's area by the number of pieces:
- 50 × 70 (0.35 m²), 9 flyers: about 0.039 m² per flyer.
- 35 × 50 (0.175 m²), 4 flyers: about 0.044 m² per flyer — more paper per piece, even though the sheet is smaller.
- 64 × 90 (0.576 m²), if the press takes it: 16 flyers, about 0.036 m² per flyer — the cheapest of the three.
Add the waste sheets
Sheets needed = quantity ÷ pieces per sheet, rounded up, plus waste for make-ready and running. 5,000 flyers at 9 per sheet is 556 sheets before waste. The waste allowance depends on the press, the number of colours and finishing; each shop has its own figures, and they belong in the calculation from the start, not as an afterthought.
Paper is bought by weight: area × grammage gives the weight of one sheet, and the paper cost follows from that.
Mind the grain
Paper has a grain direction. For anything that folds or creases — book pages, covers, cartons — the grain should run parallel to the fold or the spine, otherwise the fold cracks or the pages won't lie flat. That sometimes means choosing the layout that gives fewer pieces per sheet. For flat work such as flyers and business cards, grain usually doesn't matter.