Block bottom bag calculation: pasted, pinch & valve bags
Calculate the weight of a block bottom woven bag from lay-flat width, length, patch / bottom width and valve depth, with fabric mesh and denier, coating GSM, BOPP and metallised micron. Choose the open-mouth block bottom, cement valve or 4L BOPP structure and get bag weight, laminated GSM and GPM.
Bag specification
A 1 Layer bag has no lamination. It is bare woven fabric, so there is no coating, no BOPP and no metallised film to enter. Pick a 2, 3 or 4 Layer construction above to add them.
Example rates only (₹ per kg). Real costing uses your own versioned price master in Nexora Sales & Costing.
Geometry, allowances and layer build-up follow the Nexora Sales & Costing engine: cut length from fold, hamming and patch overlap; coating and film spread over body width + 10 mm; film GSM = micron × 0.92. A liner is a separate article — use the liner calculator for it. Your plant's own constants, 29 constructions and the exact per-component result live in the app.
Costing is built from your own dated RM price master and process-wise resource rates — not from example rates. We will run your bag and your prices in a free demo.
Body, patch, valve, film, ink and thread grams with % share, plus the formula behind every value, are shown in Nexora Sales & Costing.
How block bottom bag weight is calculated
A block bottom bag (also called a pasted bottom, pinch bottom or AD*STAR-type bag) is made from a gusseted or flat woven tube whose ends are folded into a rectangular bottom and top and closed with pasted patches. A valve bag adds a valve strip at one corner for filling. Compared with a stitched sack, three things change the weight:
- Cut length includes the bottom forming: cut length = bag length + patch width + patch overlap.
- Patches: two laminated pieces cut from flat fabric, each sized from the patch width and the bag width less a 5 mm trim allowance.
- Valve strip: valve depth plus extra valve, by twice the patch width plus a 15 mm overlap.
Body weight = width × (length + patch + overlap) × 2 ÷ 1,000,000 × (fabric + coating + film GSM)
Top patch = (patch − 5 mm) × (width + extra valve − patch − 5 mm) · Bottom patch = (patch − 5 mm) × (width − patch − 5 mm)
Valve = (valve depth + extra valve) × (patch × 2 + 15 mm) ÷ 1,000,000 × (fabric + coating GSM)
Bag weight = body + patches + valve + ink (no stitching thread)
Typical block bottom specifications
- Cement 50 kg valve bag: 1000–1100 denier, 12 × 12 mesh, 20–25 GSM coating, 48–52 cm wide, 60–65 cm long, 10 cm bottom, no BOPP.
- BOPP block bottom 10–25 kg (rice, pet food, seeds): 800–900 denier, 10 × 10 to 12 × 12 mesh, 18–20 GSM coating, 18–25 µm BOPP.
- Putty / tile adhesive 20–40 kg: 1000 denier, 12 × 12 mesh, valve type, sometimes with a PE liner.
Plants differ in patch overlap, valve length and bottom forming allowance, so treat the figures here as a first check. The Nexora Sales & Costing desktop app models block bottom constructions with 80 fields including patch, valve, metallised film and liner, each traceable to its formula.
FAQ
What is the difference between block bottom and pinch bottom?
Both form a rectangular bottom from the tube. A block bottom (pasted) bag closes the bottom with a pasted patch; a pinch bottom folds and hot-melt seals the end. Weight calculation is nearly the same; pinch bottom bags have a smaller patch or none.
How much does a patch and valve add?
For a 50 × 60 cm cement bag with 10 cm bottom at 86 GSM laminated fabric, the two patches add about 10–11 g and the valve strip about 1.5 g on a bag of roughly 75 g.
Can I calculate a BOPP block bottom bag?
Yes — choose a 3L or 4L block bottom structure. Enter the BOPP micron (and metallised micron for a 4L bag) and the film weight is added to the body and the patches.