PrecisionKit

GSM to LB Paper Weight Converter

Convert paper weight between GSM, lb (text or cover basis), and points — with the parent-sheet basis and any thickness assumption always shown.

Only affects GSM/lb conversions — a category's lb basis is its own parent sheet size.

GSM cannot determine thickness on its own — pick a documented bulk-density assumption to bridge mass and thickness units.

Enter a value to convert paper weight or thickness.

Basis weight explained

A pound (lb) value is the weight, in pounds, of 500 sheets of a paper category's own “parent” (uncut) sheet size — not a fixed physical sheet. Text/book, cover, bond and bristol stocks each use a different parent size, so a 100 lb cover stock and a 100 lb text stock are not comparably heavy. GSM (grams per square meter) avoids this ambiguity because it is defined the same way regardless of category, which is why print buyers increasingly compare stocks by GSM.

Conversion formula and reference sheet sizes

  • Text / Book: 25×38 in parent sheet, 500 sheets per basis
  • Cover: 20×26 in parent sheet, 500 sheets per basis
  • Bond / Writing: 17×22 in parent sheet, 500 sheets per basis
  • Bristol / Index: 22.5×28.5 in parent sheet, 500 sheets per basis
How this is calculated
lb = GSM × parent_sheet_area_m2 × sheets_per_basis / 453.59237

This is the standard printing-industry basis weight formula, solved for either direction. Points and millimeters are length units for caliper (thickness) and are calculated independently — 1 point = 0.001 inch = 0.0254 mm — never derived from GSM unless a caliper assumption is explicitly selected.

Worked example

500 sheets of 20×26 in cover parent stock at 100 lb basis weight: area = 20 × 26 × 0.00064516 m²/in² = 0.335483 m². GSM = (100 × 453.59237) / (0.335483 × 500) ≈ 270.4 g/m².

In plain English: a 100 lb cover stock weighs about the same, per square meter, as a 270.4 GSM stock — but only when comparing within the cover category.

Choosing paper for print

Business cards and postcards typically use 250–400 GSM cover or bristol stock; flyers and brochure interiors commonly use 100–170 GSM text stock; book interiors often use 60–100 GSM text stock; covers and packaging typically use 250 GSM or heavier cover/bristol stock. These are common ranges, not fixed rules — always check your printer's specification sheet for the exact GSM they stock.

Why GSM cannot determine thickness

GSM measures mass per area, not caliper (thickness). Two stocks at the same GSM can have different thickness depending on how densely the fibers are pressed — a property called bulk. This tool only estimates thickness from GSM when you select a caliper assumption (a bulk-density approximation for a stock class), and always labels that estimate as an approximation.

Basis sheet count
500 sheets per basis for every category, per standard printing-industry practice.
Point definition
1 point = 0.001 inch of caliper (a length unit), not a mass unit.

Questions

Why do text and cover pounds differ?

A pound value is the weight of 500 sheets of that category's own parent (uncut) sheet size, and each category uses a different parent size — text/book uses 25×38 in, cover uses 20×26 in. Two stocks that feel similarly heavy can carry very different lb numbers because the parent sheet used to define "500 sheets" is different. GSM avoids this because it is always grams per square meter, independent of parent sheet size.

Can GSM be converted exactly to millimeters?

No. GSM is a mass per area, not a thickness. Two papers at the same GSM can have different caliper depending on how densely the fibers are pressed (bulk). This tool only estimates thickness from GSM when you explicitly select a caliper assumption — a documented bulk-density approximation — and always labels the result as an approximation, never an exact conversion.

Sources