Card - A guide to weight (gsm) and caliper (microns)
Card thickness or caliper is measured in microns (1000 microns = 1 mm) but frequently sold or described by weight or gsm (grammes per square meter). Paper and Card is manufactured and sold by the metric tonne in Europe, so weight has always been the dominant format when specifying paper and card.
Card, or board to give it it's proper name is sold using both caliper and weight to give the buyer more information. Commercially available card for printing and craft use usually starts at around 200 microns and finishes at around 500 microns. This is about the limit for conventional paper machines, so 2 or more sheets of card are laminated together to make thicker card.
Lastly tradition throws another terminology for card thickness at us. Card used to be and sometimes still is described in terms of how many sheets of paper thick it is eg. a commercially available 230 micron card may be 180 gsm and known as '3-sheet'. I have summarized most popular card thicknesses below, showing commercially available gsm and micron figures and hope this is of use to card buyers.
2-sheet / 200 microns / 150-160 gsm
Thin card developed originally for photo copiers, still sold mainly as a companion product for 80 gsm office stationery.
3-sheet / 230 microns / 170-180 gsm
Flexible card suitable for folding, montage, student projects, mobiles etc.
4-sheet / 280-300 microns / 210-240 gsm
6-sheet / 350-380 microns / 270-290 gsm
Medium card suitable for modelling, construction, fancy dress, card making, toppers, scrap books and sizzix etc.
8-sheet / 500microns / 385gsm
10-sheet / 580 microns / 460gsm
12-sheet / 750microns / 550-590gsm
Thick Card suitable for craft knife use, mounting, photography mounts, portfolios, framing and stage props etc.