Why is 100 lb cover not the same as 100 lb text?
U.S. basis weight is defined using category-specific basis sheet sizes, so the same lb number does not mean the same GSM across cover, text and bond stocks.
GSM is universal; “lb” depends on paper category
GSM is grams per square metre. U.S. basis weight is the weight of a 500-sheet basis ream whose sheet dimensions depend on the paper category. That is why an 80 lb text sheet and an 80 lb cover sheet are not the same stock.
| Category | Basis size used by the converter |
|---|---|
| Bond / writing | 17 × 22 in |
| Text / book | 25 × 38 in |
| Cover | 20 × 26 in |
| Index | 25.5 × 30.5 in |
Use the numbers from your actual job
The guide explains the decision; the linked calculator gives you the value for your own file or production assumptions.
Identify the paper measurement first
GSM, U.S. basis weight, sheet mass and caliper answer different questions. Use the measurement that controls the job rather than converting one number and assuming it describes every paper property.
Apply the answer to this specific question
U.S. basis weight is defined using category-specific basis sheet sizes, so the same lb number does not mean the same GSM across cover, text and bond stocks. The practical consequence should be checked with GSM to Pounds Calculator, Text Weight to GSM Calculator, Cover Weight to GSM Calculator when your own dimensions, page count, cost or production values differ from the example implied by the question.
What commonly changes the result
For “Why is 100 lb cover not the same as 100 lb text?”, the most important variables are the ones represented by the linked calculator and any provider-controlled specification. A correct arithmetic result can still be unsuitable if the source dimensions, category, page yield, trim, bleed, margin or production method were assumed incorrectly.
A better verification workflow
For Why is 100 lb cover not the same as 100 lb text?, record the source measurement or controlling specification first, then run the real job values through gsm to pounds, text weight to gsm. Keep the result with the job notes, compare it with the physical file or material, and recheck any provider-controlled rule immediately before production or upload.
Practical answer
U.S. basis weight is defined using category-specific basis sheet sizes, so the same lb number does not mean the same GSM across cover, text and bond stocks.
When the decision affects a paid print run, book upload, client order or expensive material, keep the calculation with the job notes and verify any external specification again immediately before production.