Paper Weight Explained: What GSM and lb Actually Mean
Why 20 lb bond and 50 lb offset can be the same paper, and what weight actually tells you about printing
The Two Systems Don't Line Up Because They Measure Different Things
GSM (grams per square metre) measures exactly what it says: weigh one square metre of the paper, that's the GSM. It's metric, linear, and consistent across all paper types. A 90 GSM sheet is 90 GSM whether it's bond, offset, cover, or cardstock.
The US basis-weight system measures pounds per ream (usually 500 sheets) of an uncut parent sheet, and the parent-sheet size changes depending on paper category. Bond paper uses a 17×22-inch parent. Cover stock uses 20×26 inches. Text/offset uses 25×38 inches. This is why 20 lb bond, 50 lb offset, and 55 lb text are all roughly the same paper — the reams being weighed are different sizes. The system made sense in mills and print shops a century ago. It makes no sense now, but we're stuck with it.
What Common Weights Actually Feel Like
20 lb bond (75 GSM) is standard office copy paper. It's what comes in the 500-sheet ream. Thin enough to fold easily, opaque enough for single-sided printing, borderline for duplex if you're using heavy ink coverage or dark backgrounds.
24 lb bond (90 GSM) is premium copy paper or everyday letterhead. Noticeably sturdier in the hand. Better opacity — duplex prints look cleaner. Most office printers handle it without changing a setting.
28 lb bond (105 GSM) is heavy letterhead or light brochure stock. It feels substantial. You'll want to check your printer's paper-weight spec, and you may need to tell the driver you're using heavier media so it slows down and applies more heat.
65 lb cover or 80 lb cover (176–216 GSM) is cardstock — greeting cards, postcards, presentation covers. Stiff, no flop. Many home inkjets and small-office lasers top out around 80 lb cover; check your manual's maximum media weight, usually listed in GSM or as a thickness in millimetres.
What Paper Weight Actually Affects
Opacity and show-through. Heavier paper is usually thicker and more opaque, so duplex printing looks better and you don't see the reverse side ghosting through. But coating and pulp matter too — a coated 75 GSM can be more opaque than an uncoated 90 GSM.
Feel and perceived quality. Weight is the easiest thing a reader's hand notices. A 90 GSM letterhead feels more serious than 75 GSM. A 105 GSM invitation signals effort. Past a certain point it's just signaling, but the signal works.
Printer compatibility. Every printer has a maximum media weight, and it's the binding constraint. Rollers, fuser temperature, and feed angle all assume a certain stiffness. Go past the spec and you get jams, misfeeds, or toner that doesn't fully bond. The limit is in your printer manual, often buried in "media specifications." Consumer inkjets often cap around 60–80 lb cover; office lasers may go to 90 lb cover or higher. When in doubt, test one sheet before you load fifty.
How to Choose Paper Weight
Match the job to the weight. Single-sided flyers on 20 lb bond are fine if they're headed for a bulletin board. Duplex newsletters or anything double-sided should be 24 lb bond minimum. Letterhead that represents your business should be 24 or 28 lb. Postcards that go through USPS machinery need to be at least 65 lb cover to meet the rigidity requirement. Business cards are typically 80 lb cover or heavier.
Check your printer's spec sheet for maximum media weight before you buy cardstock. If the manual lists it in GSM and your paper is marked in pounds, search "[paper type] [lb weight] to GSM" for a rough equivalent — but remember that the conversion depends on the parent sheet size, so "80 lb" alone doesn't tell you everything. The GSM number, when present, is always the real one.
Why This Mess Persists
The basis-weight system survives because US paper mills, distributors, and print shops have used it for generations, and changing every spec sheet and ordering system would be expensive and confusing during the transition. GSM is slowly gaining ground — you'll see both numbers on many reams now — but if you're buying paper in the US, you'll be reading pounds for a while yet.
The good news: once you've handled 20 lb bond, 24 lb bond, and 65 lb cover, you have the anchors. Everything else is relative to those three.
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Upload & PrintFrequently Asked Questions
Can I print cardstock on a regular inkjet printer?
It depends on the printer's maximum media weight, usually listed in the manual's specifications. Most consumer inkjets handle up to 60–80 lb cover (around 200 GSM). Check the spec before you buy a ream, and feed cardstock one sheet at a time through the manual or rear tray if your printer has one — the straight paper path reduces jams.
Why does my duplex printing look see-through?
The paper is too light or too thin for the ink or toner coverage you're using. Switch to 24 lb bond (90 GSM) minimum for duplex jobs, or reduce ink density in your print driver. Coated paper also helps with opacity, but check that your printer supports it.
What paper weight do I need for USPS postcards?
USPS requires postcards to be at least 0.007 inches thick, which typically means 65 lb cover (176 GSM) or heavier. Thinner stock will either be rejected or damaged in the sorting machines. If you're printing and mailing postcards yourself, check the current USPS postcard standards before you buy paper.
Is 28 lb paper the same as 28 GSM?
No. 28 lb bond is approximately 105 GSM. The pound measurement refers to the weight of a ream of large uncut parent sheets, not the weight per square metre. GSM is always the actual grams per square metre of a single sheet, so the numbers are on completely different scales.