Caliper (paper)
Caliper is the measure of a paper or board's thickness, typically expressed in thousandths of an inch (points or 'pt') in North America and in micrometres elsewhere. A 12-point board is 0.012 inches thick.
Caliper is measured with a dead-weight micrometer at a standardised contact pressure (TAPPI T 411). Different pressures yield different readings on the same paper, so spec sheets list the test method when caliper is a critical attribute.
Caliper and basis weight are related but not interchangeable. A heavier paper is usually thicker, but bulk (the ratio of caliper to basis weight) varies by furnish and process — a high-bulk paper feels substantial relative to its weight, which matters for packaging stiffness and book-page feel.
For folding cartons and rigid packaging, caliper is the primary strength proxy: stiffness scales roughly with caliper cubed, so a small caliper change makes a large difference in how the carton feels and performs.
Related terms
- Basis weightBasis weight is the standard measure of paper weight in the U.S., expressed in pounds per 3,000 square feet of a grade's parent sheet. Elsewhere it is reported as grams per square metre (gsm).
- Edge crush test (ECT)ECT measures the edgewise compressive strength of a corrugated board, reported in pounds per inch or kN/m. It is the standard predictor of stacking strength and has largely replaced burst strength as the spec for box certification.
Tired of looking these up by hand?
PaperFlo builds custom document automation that extracts these fields cleanly from supplier PDFs, so your team can stop typing them in.
Book a discovery call