Envelope Weight Conversion: GSM to lb, Basis Weight & Grams Chart

Introduction

Ask two suppliers for "100 lb paper" and you can receive two materials that differ by more than double in actual weight. That is not a mistake on either side — it is how the US paper-weight system works, and it is the single most common source of confusion in envelope specification.

The reason is that American paper weights are not weights. They describe how much a ream of 500 sheets weighs at that grade's own uncut sheet size — and every grade uses a different sheet size. Bond, text, cover, index, and tag each start from a different rectangle, so the same number describes a different thickness of paper in each.

This guide explains the basis sizes behind each grade, gives the conversion formula, and provides gsm-to-lb charts for every grade used in envelope making. For which paper to choose in the first place — finishes, fiber, and use cases — see our envelope paper types and weight guide; that article covers selection, and this one covers the arithmetic that lets you compare materials across systems.

Why "lb" Is Not a Weight

A paper's pound value answers a specific question: what does a ream of 500 uncut sheets weigh, at this grade's standard sheet size?

Because the basis size differs by grade, the comparison only works within a grade. A 24 lb bond and a 24 lb text are not the same material — the bond is measured on a much smaller sheet, so its 24 lb represents a thicker paper.

Grammage is the more portable measure precisely because its basis never changes.

The Basis Sizes Behind Each Grade

This table is the root of the whole problem — and the reason the same number means different papers.

The spread is large: bond is measured on a sheet of 374 square inches, text on one of 950 — two and a half times the area. That single fact explains almost every "100 lb" surprise.

The Conversion Formula

Two conversions, both reversible.

The constants: 453.592 grams per pound, 500 sheets per ream, 1550 square inches per square metre.

Worked example — 20 lb bond:

The same arithmetic on 20 lb text would give a very different answer — which is the point.

Bond Grade: gsm Equivalents

Bond is the classic envelope and letterhead grade, measured on a 17 × 22 sheet.

The widely repeated equivalence is that 20 lb bond is close to 75–80 gsm, which is why US office paper and European A4 feel similar.

Text / Book Grade: gsm Equivalents

Text — also called book or offset — is measured on the much larger 25 × 38 sheet, so its numbers run higher for the same actual weight.

The comparison that trips people up: 50 lb text is about 74 gsm, while 24 lb bond is about 90 gsm. The text number looks larger and the paper is lighter.

Cover Grade: gsm Equivalents

Cover — the card stock used for stiff envelope backs and heavy inserts — is measured on a 20 × 26 sheet.

The famous "110 lb cardstock" is roughly 298 gsm — a genuinely rigid material, which is why it is often confused with a heavier bond.

Index, Tag and Newsprint

These grades appear less often in envelopes but come up in specialty and postal work.

Newsprint illustrates the basis-size effect in reverse: 22 lb newsprint is only 36 gsm, far lighter than 20 lb bond at 75 gsm, because newsprint is measured on a sheet more than twice as large.

The Same Number, Different Paper

This is the table to keep. Applying the formula at 100 lb across grades:

A "100 lb" envelope could be a light 148 gsm text stock or a rigid 376 gsm bond — a difference of two and a half times, from the same instruction.

The safe habit is to specify both systems — for example "90 gsm / 24 lb bond" — so the supplier cannot resolve the ambiguity the wrong way.

Envelope Self-Weight and Postage

Envelope weight matters beyond feel, because the envelope itself consumes part of the first weight bracket.

For a single letter the envelope is a small share of the total. For a bulk mailing of thousands, the difference between two paper weights is measurable in postage.

One caution worth knowing: the stated basis weight is a nominal figure, and actual production runs vary slightly around it. Ask the supplier what tolerance applies to the grade you are buying rather than assuming the number is exact — and if weight is critical, ask for the measured value of the batch.

Applying This to Envelope Specification

A short procedure for specifying weight without getting caught out.

Print and finishing behaviour follows weight and coating: a heavier, coated sheet takes foil and emboss differently from a light uncoated one, which is worth confirming against your file specification — see our guide to print-ready files. Weight also feeds directly into material cost, which we cover in our envelope printing cost guide.

Common Mistakes

Note the last row: envelope size conversion is a simple 25.4 mm-per-inch multiplication, while weight conversion depends on the grade. The two look similar and are not.

Conclusion

Envelope weight conversion works because grammage has a fixed basis — one square metre — while US pound values are measured against a different sheet size for every grade. Bond uses 17 × 22, text uses 25 × 38, cover uses 20 × 26, index uses 25.5 × 30.5, and tag and newsprint use 24 × 36. That is why 100 lb text is roughly 148 gsm while 100 lb bond is roughly 376 gsm.

Convert with the grade's own basis size, state both systems on the order, and never quote a pound value without its grade name. For choosing between papers — finishes, fibers, and the uses each suits — see our envelope paper types and weight guide.

Specifying a paper weight and want it confirmed before the run? Request a quote with the grade and grammage you need.