Paper Thickness to GSM Calculator

GSM stands for "grams per square metre" — the weight of one square metre of the paper, regardless of sheet size. It's the standard international measure of paper weight (grammage) and is printed on most paper specification sheets and packaging.

Thickness (also called caliper) is the physical depth of a single sheet, usually measured in microns (thousandths of a millimetre) or sometimes in mm or thousandths of an inch (points). Two papers with the same GSM can have different thickness if they're made or finished differently, because thickness also depends on the paper's density.

Thickness (microns) = GSM ÷ density (g/cm³). Density isn't printed on most packs, so this calculator uses a typical reference density for everyday uncoated paper (0.77 g/cm³) as an editable default — if you know your paper's actual density, enter it for a more precise result.

GSM (g/m²) = thickness (microns) × density (g/cm³). As with the reverse conversion, the accuracy depends on how close the density figure you use is to your actual paper's density.

Because GSM measures weight per area, not thickness — it says nothing about density. A coated, calendered, or compressed paper packs more mass into a thinner sheet (higher density), while an uncoated, bulky, or "antique" finish paper spreads the same weight over a thicker sheet (lower density). Two 90gsm papers can differ noticeably in caliper for this reason.

It's the mass per unit volume of the paper, in grams per cubic centimetre (g/cm³) — effectively how tightly the fibres are packed. It's the mathematical link between GSM (weight per area) and thickness (depth), since density = GSM ÷ thickness for a flat sheet. Printers sometimes refer to the inverse of density as "bulk".

Everyday uncoated office and print paper generally works out at roughly 0.71 to 0.83 g/cm³. Manufacturer data sheets quote grammage and caliper rather than density, so you divide one by the other: Navigator's office range gives 80gsm at 110 micron (0.73 g/cm³) and 90gsm at 115 micron (0.78 g/cm³). This calculator defaults to 0.77 g/cm³ as a mid-range starting reference — coated, board, or specialty stocks are often denser (or sometimes bulkier), so adjust the density if you know a more specific figure.

A standard ream is 500 sheets. Ream weight (kg) = GSM × sheet area (m²) × 500 ÷ 1000. For A4 (0.06237m²) at 80gsm, a 500-sheet ream weighs about 2.5kg; this calculator computes the same formula for your entered GSM, sheet size, and quantity.

Yes — if you already know both figures (for example, from a supplier spec sheet), enter both and the calculator will show the "implied density" from your own numbers and compare it against the reference density, flagging whether the pair looks typical or suggests a different stock type such as board or coated film.

It usually means the paper isn't a standard uncoated stock — coated art papers, boards, laminates, and speciality materials (such as synthetic or foam-backed sheets) can have quite different densities from everyday office paper. It can also mean one of the entered figures (GSM or thickness) doesn't match the specification you intended to check.

The physics (density = GSM ÷ thickness) applies to any flat sheet material, including card and board. The default 0.77 g/cm³ reference density is calibrated for everyday uncoated paper, not board — if you're checking card or board stock, enter its known density for an accurate estimate.

GSM on its own doesn't tell you how heavy a real batch of paper will be — knowing that a 500-sheet A4 ream weighs about 2.8kg (at 90gsm) is directly useful for postage costing, storage planning, or checking a supplier's stated pack weight, which a bare GSM figure can't answer.

Points (sometimes called "mils" in the US) are another caliper unit, equal to one thousandth of an inch (25.4 microns). This calculator reports thickness in microns and millimetres, the units most commonly used on UK and European paper specification sheets.

It depends entirely on how close the density figure used matches your actual paper. The 0.77 g/cm³ default is a reasonable starting point for everyday uncoated paper, but coatings, fillers, and finishing can shift real density by 20% or more. For a precise figure, use your supplier's exact specification or a direct micrometer measurement rather than an estimate.

Leave the density field at its default (0.77 g/cm³) for a reasonable estimate on everyday uncoated paper, or check your paper supplier's specification sheet — many quote both GSM and caliper, from which you can calculate the exact density yourself using this calculator by entering both figures.