How thick is a standard A4 piece of card in mm?

A standard A4 piece of card typically has a thickness ranging from 0.25 mm to 0.5 mm, depending on its weight and type. Common weights for card range from 200 to 300 gsm (grams per square meter), which corresponds to this thickness range. For specific applications, such as business cards or postcards, thicker options may be used, but the standard thickness is generally within this range.