Last updated: 2026-07-13

Paper Weight

Paper weight is written two ways. Most of the world uses grammage — grams per square metre (gsm), the mass of a one-square-metre sheet. The United States uses basis weight — the weight in pounds (lb) of a 500-sheet ream cut to a paper grade's standard size. Grammage is a single physical quantity, but the pound rating only makes sense once the grade is known, so this converter asks for the grade and then moves between the two units in either direction.

Why the pound rating depends on grade

Basis weight is the weight of one ream (500 sheets) of paper cut to that grade's basic size. Each grade has a different basic size, so the same grammage lands on a different pound number:

Because the basic sizes differ, 80 lb text and 80 lb cover are not the same sheet at all — 80 lb text is a mid-weight book paper near 118 gsm, while 80 lb cover is a stiff card near 216 gsm. Grammage removes this ambiguity, which is why print shops outside the US quote paper in gsm.

The conversion formula

Grammage relates to basis weight through the area of one ream and the definition of a pound:

where $W$ and $H$ are the grade's basic-size dimensions in inches, $453.59237$ is grams per pound, $500$ is sheets per ream, and $0.00064516$ is square metres per square inch. The whole fraction collapses to a single per-grade factor $k$:

Worked example

A 60 lb text-weight sheet is quoted for an international print run that expects gsm. Using the text/book factor:

So 60 lb text rounds to about 89 gsm — the value a supplier abroad will recognise. Reversing the same factor, a 120 gsm text sheet works out to $120 \div 1.4801 \approx 81$ lb text.

Common weight equivalents

Rounded to whole numbers, these are the pairings seen most often:

Weight, thickness and related tools

Grammage measures mass per area, not thickness. Two sheets of the same gsm can differ in caliper (thickness) depending on how bulky or calendered the stock is, so a heavier gsm usually feels thicker but is not a direct thickness measurement. For sheet dimensions rather than weight, see the Paper Size Converter; for the point and pica units used in typesetting on those sheets, see the Typography Unit Converter.

Limitations

The factors here use the standard US basic sizes for each grade. Some speciality and international grades use different reference sizes, and a few regions define their own ream counts, so a supplier's own chart takes precedence when it differs. The converter also rounds to the precision of each unit; for production ordering, confirm the exact grammage on the manufacturer's specification sheet.