Paper weight converter
"80 lb" means three different sheets depending which ream was weighed: the US basis system weighs 500 sheets of a stock's own uncut size, so every family converts by a different factor. gsm needs no such context, which is why the rest of the world uses it. Convert either way — the factors are exact ream arithmetic, and the table shows your sheet in all five bases at once.
Grams per square metre is the same number in every country and every shop.
Which ream was weighed. This is the whole reason "80 lb" is ambiguous.
| Basis | This paper, in lb | Ream that was weighed |
|---|---|---|
| Text | 80 lb | 25×38 in |
| Cover | 43.8 lb | 20×26 in |
| Bond | 31.5 lb | 17×22 in |
| Index | 65.5 lb | 25.5×30.5 in |
| Bristol | 54 lb | 22.5×28.5 in |
One sheet, five names. Text 80 lb, bond 44 lb and index 50 lb are the same paper — which is why serious specs quote gsm and let the reams argue among themselves.
Exact ream arithmetic, on this machine. Thickness is a different question — the spine calculator carries real calipers per stock.
Why “80 lb” is ambiguous
A ream of 500 sheets at 25×38 in (Text) weighs differently from 500 sheets at 17×22 in (Bond) even when the paper is identical — the reams contain different amounts of paper. So Text 80 lb, Bond 44 lb and Index 50 lb are the same sheet: about 118 gsm. Serious specs quote gsm and let the reams argue among themselves; when a US printer insists on pounds, this gives you the exact number for the exact basis.
| The anchors | In lb | In gsm |
|---|---|---|
| 20 lb Bond — office paper | 20 lb Bond | 75 gsm |
| 80 lb Text — book stock | 80 lb Text | 118 gsm |
| 100 lb Cover — card | 100 lb Cover | 270 gsm |
| The chat-book page | — | 80 gsm |
Weight is not thickness: two sheets at the same gsm caliper differently depending on bulk. For millimetres per sheet, the spine calculator carries real calipers per stock.
Questions people actually ask
Is gsm the same as grammage?
Yes — grams per square metre, the ISO measure. Cut a square metre of the sheet, weigh it, done. It needs no ream size, which is the entire advantage.
Which basis should I pick?
Whichever one your printer or paper merchant quoted. Text and Cover cover most book work; Bond is office stock; Index and Bristol are card families. If nobody said, ask — the difference between Text and Cover at '80 lb' is nearly 100 gsm.
What about points (pt) for board?
Points are thickness, not weight — 1 pt is 1/1000 inch, about 0.025 mm. Greyboard at 2.5 mm is about 98 pt. That is a caliper conversation, and the spine and case tools handle those in millimetres.
Are the conversions rounded?
Each factor is 453.59237 g divided by 500 sheets times the basis sheet's exact area — carried to full precision and rounded only for display. The table you print will survive an audit.
The books this site prints use 80 gsm — 0.10 mm a sheet, exactly.
See the paper it becomesThis is one of the tools — or see everything we’ve written.