📄 Paper Weight Calculator

How to Calculate Paper Weight

Enter the sheet dimensions in inches, the paper's GSM (grams per square meter), and how many sheets, and the calculator returns the total weight in pounds and kilograms, the per-sheet grams, and the US bond-weight equivalent. Printers use this for postage estimates; offices use it to avoid overloading shelves and mail slots.

The Formula

A square meter is 1,550 square inches, so dividing the sheet's square inches by 1,550 gives its fraction of a square meter, and multiplying by GSM gives grams per sheet. A ream (500 sheets) of 8.5x11 at 75 gsm: each sheet is 4.5 g, the ream is 5.0 lb (2.26 kg), and 75 gsm equals 20 lb bond. That last number is why office paper is called "20 lb paper."

Worked Example

One hundred sheets of 8.5x11 cardstock at 120 gsm: each sheet weighs 7.2 g, and the stack weighs 1.6 lb (0.72 kg). The bond equivalent is 31.9 lb, which a US paper supplier would call 32 lb bond or roughly 80 lb cover. Same physical paper, three different numbers: that is the paper industry for you.

GSM vs US Basis Weight

GSM is beautifully simple: grams per square meter, one number worldwide. The US system is historical: "basis weight" is the pounds of a 500-sheet ream at the paper's basic size, and basic sizes differ by paper type (17x22 for bond, 20x26 for cover, 25x38 for book). That is why the same sheet can be 32 lb bond or 80 lb cover: different basic sizes, different ream weights, same paper. When comparing stocks, convert everything to GSM first.

Postage and Mailing

USPS First-Class letter rate covers up to 1 oz (28.35 g): about six sheets of 75 gsm letter paper plus an envelope. Knowing per-sheet grams lets you count sheets against the ounce instead of guessing at the post office. For bulk mailings, the total-pounds figure sizes the boxes and the shipping cost in one step.

Choosing Paper by GSM

Everyday printing: 75-90 gsm. Letterhead and resumes: 90-120 gsm for a substantive feel. Brochures: 130-170 gsm. Postcards and covers: 200-300+ gsm. Heavier is not always better: home printers jam above about 200 gsm, and postage climbs with every gram. Match the weight to the job.

Letter vs A4: Weight Across Sizes

US Letter (8.5x11) and A4 (8.27x11.69) are nearly the same area: 93.5 vs 96.7 square inches, about 3.4 percent apart. At the same GSM, an A4 sheet weighs about 3.4 percent more than a Letter sheet, and a 500-sheet ream follows suit. The difference is invisible on a desk but matters in bulk: 10,000 A4 sheets at 80 gsm weigh about 50 kg versus 48 kg for Letter. Enter either size above and the calculator handles the area math either way.

A Second Worked Example: The Mailing

Five hundred flyers, 8.5 by 11 inches, at 100 gsm. Grams per sheet: 8.5 times 11 divided by 1550 times 100 is 6.03 g. The stack: 6.03 times 500 is 3,015 g, or 3.02 kg, which is 6.65 lb. Add envelopes and the mailing weighs around 8 lb total. That number decides the postage tier and whether the mail house charges by piece or by pound. Run it before you print, not after, because paper choice is the cheapest variable and reprinting on lighter stock is the most expensive lesson.

Compare with the same flyer on 75 gsm office paper: 4.5 g per sheet, 2.26 kg per 500, about 5 lb. The heavier stock costs 1.65 lb of postage per 500 pieces but feels substantially more premium in the hand. That trade is the entire direct-mail business in one calculation.

Basis Weight Decoded: Bond, Book, Cover, Text

The US names confuse everyone because the same paper gets different numbers. Twenty-pound bond, 50-pound book, and 75 gsm are the same paper: the number changes because each paper type is weighed at a different "basic size" (17x22 for bond, 25x38 for book). GSM never lies because it is always grams per square meter. When comparing papers, convert everything to GSM first.

The practical pairs to memorize: 20 lb bond = 50 lb book = 75 gsm, standard office paper. 24 lb bond = 60 lb book = 90 gsm, premium letterhead. 65 lb cover is about 175 gsm, sturdy postcard stock. 80 lb cover is about 215 gsm, business-card territory. And the trap: 80 lb cover and 80 lb text are wildly different papers. Cover is weighed at 20x26 basic size, text at 25x38, so 80 lb cover is far heavier than 80 lb text. Never compare numbers across paper types; convert to GSM.

Common Paper-Weight Mistakes

First: the cover-versus-text trap above. "80 lb" means nothing without the paper type. Second: forgetting that a "ream" is not always 500 sheets. Some papers sell in 250-sheet reams, and the basis weight math assumes 500. Third: ignoring packaging in postage estimates. The paper weight is the floor; envelopes, inserts, and the mailer itself add real ounces.

Fourth: shelving math without the shelf. A case of 10 reams of 20 lb bond weighs about 50 lb; a case of cardstock can top 80. Know the loaded weight before you stack cases five high on a particleboard shelf. Fifth: printer limits. Home printers often cap at 60-65 lb cover; feeding 80 lb cover through one causes jams and can damage the feed rollers. Check the printer's max stock weight against your paper's GSM before the big print run.