Paper weight explained: GSM vs lb (and why 'lb' is so confusing)

Updated 2026-10-12

The 10-second version: GSM tells you how heavy the paper actually is. “lb” (basis weight) is the weight of 500 sheets at that stock’s base size — and the base size differs by stock. That is why the same lb number means a different paper for text, cover and bond.

Why 50 lb text and 50 lb cover are not the same paper

Weigh 500 sheets of 50 lb Text paper and you are weighing large parent sheets — 25 × 38 in. Weigh 500 sheets of 50 lb Cover paper and you are weighing much smaller sheets — 20 × 26 in.

For both stacks to hit the same 50 lb mark, the Cover sheet has to be much thicker and heavier per sheet than the Text sheet. Cut both down to the same size and weigh them and you get very different results:

• 50 lb Text feels thin and flexible (like book pages) → about 74 gsm
• 50 lb Cover feels thick and rigid (like a postcard) → about 135 gsm

So “lb” on its own is meaningless. It only means something together with the stock it belongs to — always read it as “lb text” or “lb cover”.

Quick conversion guide — lb → gsm (multiply)

To go the other way (gsm → lb), divide by the same number. Factors are derived from the standard US base sizes and are approximate — mills vary slightly.

Business cards

Business cards are cover stock, so use the cover row. That means:

• 80 lb cover ≈ 216 gsm
• 100 lb cover ≈ 270 gsm
• Most business cards are 300–400 gsm (roughly 110–147 lb cover)

Reading a spec sheet

• “80 lb text” = a normal writing/book paper — not cardstock.
• “80 lb cover” = a stiff card — about 216 gsm.
• When a number has no stock label, ask. It changes everything.
• GSM is the safe international number — it is the same at any sheet size, so it compares cleanly across countries.

FAQ

Why does the same gsm give a different lb for each stock? Because lb is measured against that stock’s base size, and the base sizes differ (bond 17 × 22, text 25 × 38, cover 20 × 26 in). So 210 gsm is about 56 lb bond, 142 lb text or 78 lb cover — the same paper weight, three different lb numbers.

What is 20 lb bond in gsm? About 75 gsm (20 × 3.760) — the familiar “standard office paper”.

Is 300 gsm the same as “16 lb”? No. 300 gsm is close to 110 lb cover, not 16 lb. Any small “16 lb” figure is a text weight and is far lighter.

Does GSM tell me the thickness? Not directly. GSM is weight per area; two papers of the same gsm can differ slightly in thickness (caliper). See card caliper and thickness.