About the Paper Thickness Calculator
This tool computes a sheet's caliper (thickness) from its basis weight and density, then derives two numbers printers and buyers actually plan around: bulk (how many sheets stack to one inch) and the total height of a stack or ream for a given sheet count.
The formula
Paper thickness follows directly from the definition of density. Basis weight (grammage) is mass per unit area, in grams per square meter (g/m²). Thickness is volume per unit area. Since density equals mass divided by volume, dividing basis weight by density gives thickness:
Caliper (µm) = Basis Weight (g/m²) ÷ Density (g/cm³)
The unit conversion works out so that g/m² divided by g/cm³ gives micrometers directly — no extra conversion factor needed. For example, standard 80 gsm office paper at a typical density of about 0.80 g/cm³ gives a caliper of 80 ÷ 0.80 = 100 µm, or 0.1 mm per sheet, which matches what a micrometer reads on ordinary copy paper.
From caliper to bulk and stack height
- Sheets per inch (bulk): the reciprocal of the caliper expressed in inches — 1 ÷ Caliper (in). A thinner sheet packs more sheets into an inch.
- Stack or ream height: Caliper × Number of Sheets. This is how printers estimate the spine width of a book block or the height of a ream before it is banded.
Choosing a density value
If you have the manufacturer's caliper spec or a micrometer reading, use it directly instead of guessing density — it will always be more accurate than an assumed figure. When you only know the basis weight, typical density ranges by furnish and finish: uncoated bond and copy paper run roughly 0.7–0.9 g/cm³, coated/glossy stocks run denser at about 1.0–1.1 g/cm³, and bulky uncoated book papers can run as low as 0.55–0.65 g/cm³. These are general industry ranges, not a guarantee for any specific mill's product — coating, calendering, and furnish all shift the real number.
How to get the best results
- Use the basis weight printed on the ream wrapper or spec sheet (g/m² or "gsm"), not the pound-based US basis weight, which depends on a reference sheet size and is not directly comparable across grades.
- If you know the actual caliper from a micrometer, back-calculate density instead: Density = Basis Weight ÷ Caliper, then use that density for other grammages of the same stock.
- For binding and spine-width work, measure a real stack when possible — compression under banding or clamping can shave a few percent off the calculated height.
Practical context
This calculator gives the theoretical caliper implied by basis weight and density. Real paper varies sheet to sheet and can compress slightly in a bound stack, so treat the result as a close estimate — verify with a micrometer or the mill's data sheet before finalizing a print spec, binding design, or packaging fit.