The physical thickness of paper/paperboard in an uncompressed state, expressed in µm (microns) or mm.
How it’s measured: Using a micrometer/thickness gauge under specified pressure and sampling points; report the average value.
Relation to basis weight (GSM): Caliper ≠ GSM. Fiber type, fillers, and calendering mean the same GSM can have different calipers, and vice versa.
Performance impact: Generally correlates with stiffness/rigidity, cushioning, and some barrier/insulation properties; excessive caliper can increase cost and hinder folding.
Typical ranges (for reference):
Coated/text papers: 70–200 µm
Folding carton boards (300–400 gsm): ~350–550 µm
Greyboard/chipboard: ~0.8–3.0 mm
Quick conversions: 0.5 mm = 500 µm; 350 µm = 0.35 mm.
Tolerance: Specify a target caliper and acceptable tolerance (e.g., ±0.03 mm) on samples and purchase orders to ensure consistency.