Paper weight labels look simple on a ream wrapper, yet a single number printed under the word "lb" can mean wildly different physical sheets depending on which grade you are holding. A pound is a pound only if you also know whether you are looking at bond, text, cover, index, tag or bristol paper, because each grade uses a different basis size for that pound rating. Skip the grade and the same "100 lb" can mean a light 148 gsm sheet of text paper or a heavy 270 gsm sheet of cover stock — almost double the thickness for identical text on the wrapper. Understanding the conversion between GSM and pounds by grade is the foundation for matching paper to a printer's media menu, ordering the right stock from a catalog, or sanity-checking a spec sheet. This guide walks through the conversion, lays out the six grades and their basis sizes, and shows how to use a Paper Weight Converter to translate any label in seconds.
The GSM System: One Number, One Meaning
The metric half of this puzzle is the easy one. GSM — grams per square meter — is defined as the mass, in grams, of exactly one square meter of paper. Because the reference area is fixed and never changes regardless of the paper's grade, GSM values compare directly across every stock: a 200 gsm sheet of cover is heavier than a 120 gsm sheet of bond, no matter what either sheet is called in the catalog. This is also why printers in countries that use the metric system typically list paper weight in GSM on their media menus without needing a stock selector. A higher GSM is always a heavier, thicker sheet, and a lower GSM is always lighter and thinner. GSM needs no paper-type setting at all — the same 90 gsm means the same actual paper whether the wrapper calls it bond, text or writing. That invariance is what makes GSM the universal standard for comparing paper across brands, regions and grades.
Why the US Pound Weight Changes With the Grade
The US pound basis weight is a relic of the ream-and-basis-size system. A paper's pound rating is the total weight of one ream — 500 sheets — of that grade cut to a defined parent size called the basis size. The catch is that each grade uses a different basis size, and the parent sheet you weigh is therefore a different physical area for each grade. Cover and bond can carry the same number printed on the wrapper but represent entirely different actual paper weights once you convert them to GSM.
Under the hood, each grade has its own conversion factor between pounds and GSM, derived directly from its basis size:
- Bond ≈ 3.76
- Text ≈ 1.48
- Cover ≈ 2.70
- Index ≈ 1.81
- Tag ≈ 1.63
- Bristol ≈ 2.19
The formula is gsm = lb × factor, so 100 lb cover is 100 × 2.70 = 270 gsm, while 100 lb text is 100 × 1.48 = 148 gsm. The same 100 lb label produces results that differ by nearly a factor of two — exactly why picking the grade before converting matters. Skip the grade and the answer can be off by a hundred grams per square meter, which on a printer is the difference between plain paper feeding cleanly and cardstock jamming in the rollers. The factors themselves are not arbitrary: each one is computed from the grade's basis size using 1 in² = 0.00064516 m² and 1 lb = 453.59237 g, then resolved into gsm = lb × factor.
The Six Paper Grades and Their Basis Sizes
The grade drives everything. Here are the basis sizes that define each conversion factor, taken from the standard definitions used across the printing industry:
| Paper Grade | Basis Size (inches) | GSM per Pound |
|---|---|---|
| Bond, Writing, Ledger | 17 × 22 | ≈ 3.76 |
| Text, Book, Offset | 25 × 38 | ≈ 1.48 |
| Cover | 20 × 26 | ≈ 2.70 |
| Index | 25.5 × 30.5 | ≈ 1.81 |
| Tag | 24 × 36 | ≈ 1.63 |
| Bristol | 22.5 × 28.5 | ≈ 2.19 |
A larger basis size spreads the same pound weight across more square meters, so the same number translates to a lower GSM. Cover's smaller 20×26 sheet is what makes its pound rating land so much heavier than text's 25×38 sheet, and index's 25.5×30.5 sheet is the reason 90 lb index is roughly 163 gsm rather than the 270 gsm that 100 lb cover delivers. Bond and writing share the 17×22 basis, text and book paper share 25×38, and the three heavier cardstock-family grades — cover, index and bristol — each get their own parent size tuned to thicker sheets. Knowing which basis size belongs to your wrapper is the single fastest way to tell whether "100 lb" is going to behave like light book paper or thick greeting-card stock.
Convert Paper Weight to the Right Unit in Three Steps
Whether you are sizing up a ream at a print shop or feeding a heavy sheet through a home printer, the math you need to apply to the paper's label is identical. The Paper Weight Converter handles it in your browser:
- Pick the direction. Use the toggle to choose lb → gsm or gsm → lb. Pick the direction your printer's media menu expects, or the direction that matches the label on your paper ream.
- Type the paper weight into the value field. Enter the number from the wrapper — 80 if the pack says 80 lb, 120 if the spec sheet says 120 gsm.
- Choose the paper type and read the result. Select bond, text, cover, index, tag or bristol, and the converted value appears. Tick Compare across all paper types to see the same pound number expressed as a GSM for every grade at once — the fastest way to see how far apart the grades really are.
If your result lands a gram either side of another chart, that is normal. Different vendors round the underlying constants slightly differently, but rounded to the nearest whole GSM the numbers match standard printing conversion tables. The math itself runs entirely client-side, so the value you enter never leaves your machine. The converter is built for quick label lookups rather than bulk batch conversions, so for one-off checks it can save the arithmetic step that traditionally trips people up between pounds and grams.
Common Paper Weight Checkpoints
Use these reference points as quick sanity checks before you commit to a setting. They come straight from the conversion factors above:
| Label on the Pack | Approximate GSM |
|---|---|
| 20 lb bond | ≈ 75 gsm |
| 24 lb bond | ≈ 90 gsm |
| 70 lb text | ≈ 104 gsm |
| 80 lb text | ≈ 118 gsm |
| 65 lb cover | ≈ 176 gsm |
| 80 lb cover | ≈ 216 gsm |
| 90 lb index | ≈ 163 gsm |
| 100 lb cover | ≈ 270 gsm |
Notice how two entries with the same pound number diverge: 100 lb text is about 148 gsm, while 100 lb cover is about 270 gsm — almost double. If your spec sheet shows only GSM and your pack only shows pounds, run the label through the converter with the correct grade before you trust either number. The "80 lb cardstock" sold in craft and office supply stores is almost always 80 lb cover at about 216 gsm, not 80 lb text at 118 gsm — pair the number with its grade or the answer can be off by a hundred GSM. Once you internalize a few of these anchor points, you can roughly estimate any label in your head without running it through the tool.
What "Compare Across All Paper Types" Actually Shows
The converter's Compare across all paper types option is the most useful setting for understanding how the grades diverge. Type a single number — say, 80 lb — and instead of getting one answer, you get six: one for bond, text, cover, index, tag and bristol. That single screen shows exactly how much a pound label can swing depending on the grade, which is the insight most catalogs and spec sheets bury in footnotes. It is also a quick way to spot mislabeled stock: if a wrapper claims "100 lb" and the converter places it near 270 gsm, you are holding cover; if it lands near 148 gsm, you are holding text. The comparison view turns the converter from a one-shot math helper into a cross-grade reference for the entire office, and it is what makes the tool worth bookmarking for anyone who orders print stock on a regular basis.
Put the Converter Output to Work on a Printer
Once you have the converted GSM value, the practical use is to align that number with what your printer's media menu actually accepts. Most modern printers hide raw GSM behind a named media type — Plain, Thin, Thick, Cardstock, Heavy, Label, Envelope — and each name corresponds to a built-in GSM band. On a typical inkjet or laser, Plain covers roughly 60–90 gsm, Thick sits around 91–120 gsm, Cardstock covers 121–200 gsm, and Heavy handles anything above that up to the printer's stated maximum. The job is to find the band that contains the GSM the converter returned and pick that name from the menu. For printers that expose GSM directly, the answer is simpler still: enter the number the converter returned and skip the named media type. The conversion math itself does not change between brands; only the menu layout does. For a brand-specific walk-through on HP machines, see how to change paper thickness on HP printer by GSM and lb; the underlying paper-weight math is the same one this guide explains.
Quick Sanity Checks Before You Print
Before you commit to a long print run, walk through these checks. If the converter's output sits roughly between 70 and 90 gsm and your pack says 20 lb bond, you are looking at standard copy paper — Plain on most drivers and fine for the main cassette. If the result is closer to 100–120 gsm and the pack says 24 lb bond or 70–80 lb text, switch to the Thick or Thin Cardstock media band and feed from a rear or manual slot rather than the main tray. Values above 150 gsm almost always mean cardstock, cover or index, and you should expect to load one sheet at a time, use the rear feed, and extend any output tray support.
If your printer consistently smudges, jams or pulls multiple sheets on heavy paper, the most common cause is leaving it on the Plain setting while loading actual cardstock. Recheck the GSM the converter returned, then recheck the paper type you selected in the tool, then recheck the media type on the printer. Those three numbers have to agree, in that order, before the paper feeds and lays down cleanly. Adjust the paper-thickness lever on machines that still have one — most older lasers and copiers expose a small dial or slider next to the tray that has to match the grade as well — and you will cut misfeeds and ghosting almost immediately. With the grade paired correctly and the converter's number confirmed against the table above, the rest of the workflow is just printer housekeeping.
For a deeper look, see Rated Pressure vs Design Pressure: What's the Difference.