Paper Weight Converter
20 lb bond and 50 lb text are the same paper. US basis weight depends on a parent sheet that differs by paper type.
The same paper, in every naming system
Every row below is the identical sheet. Only the label changes.
20 lb bond and 50 lb text are the same paper
75.2 gsm against 74.0 gsm. You could not tell them apart by hand, and the numbers on the wrapper differ by two and a half times. This is not a mistake anyone made — it is how the system works.
A US basis weight is the weight of 500 sheets of the parent size, and the parent size is different for every kind of paper. Bond is cut from 17 × 22 inches; text is cut from 25 × 38. A ream of the larger parent weighs more for the same thickness of paper, so the number is bigger. Across the six common types the scale spans 2.54 times from end to end.
Which means a pound figure quoted without its paper type is not a weight at all. "24 lb paper" could be 90 gsm bond or 36 gsm text — a sheet you could not see through, or one you almost could. Grams per square metre has none of this: mass over area, one number, no parent sheet, no type.
What a pound is worth in each type
| Type | Parent sheet | Area | gsm per pound | |
|---|---|---|---|---|
| Bond / writing | 17 × 22 in | 374 sq in | 3.76 | Ordinary copier and letterhead paper. The 17 x 22 parent is exactly four sheets of Letter. |
| Cover / card | 20 × 26 in | 520 sq in | 2.70 | Card stock for covers and business cards. |
| Bristol | 22.5 × 28.5 in | 641.25 sq in | 2.19 | Heavy drawing and card stock. |
| Index | 25.5 × 30.5 in | 777.75 sq in | 1.81 | Stiff, smooth stock for index cards and tabs. |
| Tag | 24 × 36 in | 864 sq in | 1.63 | Tough stock for tags and hang labels. |
| Text / book | 25 × 38 in | 950 sq in | 1.48 | Book and brochure stock. The largest common parent, so its pound numbers are the biggest. |
The smaller the parent sheet, the steeper the scale — bond has the smallest parent and so the biggest gsm per pound, which is why bond numbers look small and text numbers look large for the same paper.
What each weight is actually for
Bands rather than points — paper is made to a tolerance, and nothing changes at exactly 200 gsm.
| Weight | Typical uses | |
|---|---|---|
| 0–60 gsm | Very light | Tracing, airmail, gift tissue, flimsy copies. Shows through badly and jams some printers. |
| 60–90 gsm | Everyday | Copier and printer paper, letterheads, notepads. 80 gsm is the usual office default. |
| 90–120 gsm | Heavy office | Better letterheads, reports, flyers printed both sides. Noticeably more substantial in the hand. |
| 120–160 gsm | Light card | Posters, quality flyers, book covers, origami that needs to hold a crease. |
| 160–220 gsm | Card | Greeting card inserts, menus, folders, papercraft that must stand up on its own. |
| 220–300 gsm | Card stock | Greeting cards, invitations, tags, die-cutting. Most home cutters handle this range. |
| 300–400 gsm | Heavy card stock | Business cards, premium invitations, box making. Needs scoring before folding or it cracks. |
| 400+ gsm | Board | Mounting board, packaging, model making. Cut rather than folded. |
Where the conversion constant comes from
Most sources give the number 1406 without explaining it. It is not arbitrary: a pound is 453.592 grams, a ream is 500 sheets, and a square inch is 0.00064516 square metres. Divide through and
gsm = pounds × 453.592 ÷ (500 × parent area in sq in × 0.00064516)
which collapses to pounds × 1406.14 ÷ parent area. This page computes it that way rather than storing the rounded figure, so the arithmetic is visible and there is nothing to mistype.
How to use
- Enter a weight in either box; the other follows.
- Set the paper type — the pound figure is meaningless without it.
- Read the comparison table: one sheet, six different pound numbers.
- Check it with a kitchen scale if you doubt a label.
Frequently asked questions
Why do 20 lb bond and 50 lb text feel the same?
Because they are the same paper — 75.2 gsm against 74.0 gsm. A US basis weight is the weight of 500 sheets of the parent size, and the parent size differs by paper type: bond is cut from 17 by 22 inches and text from 25 by 38. The larger parent weighs more per ream at the same thickness, so the number is bigger for identical paper.
What is basis weight?
The weight in pounds of 500 sheets of paper at its parent size, before it is cut down. It made sense in a mill where paper was handled in reams of full sheets. It makes very little sense on a wrapper in a shop, because the parent size is invisible and differs by type.
Is a pound the same in every paper type?
No, and that is the whole problem. Across the six common types the scale spans about 2.5 times: one pound of basis weight is 3.76 gsm in bond and 1.48 gsm in text. So a pound figure quoted without its paper type is not a weight at all — "24 lb paper" could be 90 gsm or 36 gsm.
What is gsm?
Grams per square metre — mass over area, and nothing else. There is no parent sheet, no type and no ream, so 80 gsm means the same thing everywhere in the world for every kind of paper. It is the reason the rest of the world stopped arguing about this decades ago.
What weight is ordinary copier paper?
Around 75 to 80 gsm, which is 20 lb bond in the US system. Cheaper paper runs 70 gsm and premium office paper 90 to 100. Below about 70 the sheet starts showing what is printed on the other side; above about 100 it stops feeding neatly through some printers.
What weight is card stock?
Usually 200 gsm and up. Business cards are typically 300 to 350 gsm, greeting cards 250 to 300. In the US system that is quoted as cover weight — 80 lb cover is about 216 gsm and 100 lb cover about 270 — which is another set of numbers for the same physical property.
Does heavier paper mean thicker paper?
Usually but not reliably. Weight is mass per area and thickness is a separate measurement, called caliper, and paper can be made bulky and light or dense and thin. Two sheets at the same gsm can differ noticeably in stiffness depending on how they were made, which is why printers sometimes specify caliper as well.
How do I check what I actually have?
Weigh it. A ream of 500 A4 sheets at 80 gsm weighs about 2.49 kg, and one sheet weighs about 5 grams. A kitchen scale and a stack of paper will settle any argument about a label, and this page shows the expected sheet and ream weight for whatever you enter.
Where does the conversion constant come from?
It is derived rather than looked up. A pound is 453.592 grams, a ream is 500 sheets, and a square inch is 0.00064516 square metres, so gsm equals pounds times 453.592 divided by 500 times the parent area times 0.00064516. That collapses to about 1406 divided by the parent area in square inches, which this page computes rather than storing.
What about text versus book versus offset?
They share the 25 by 38 inch parent, so the numbers convert identically. The names describe intended use and finish rather than a different weight system, which is a small mercy in an area that has few.
Why did the system end up like this?
Because it grew from mill practice rather than being designed. Each grade of paper had a customary parent size that suited the machines and the market, and the basis weight was simply what a ream of that grade weighed. Nobody chose to have six incompatible scales; they accumulated.
Does this send anything anywhere?
No. The conversion runs entirely in your browser and nothing is stored or uploaded.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.