Folded business cards (also called double or brochure business cards) are usually about 3.5 inches by 4 inches folded to 3.5 by 2.
When designing business cards with a bleed, use a document size of 3.75 x 2.25 inches (.25 inch bleed allowance). For a folded business card with bleed the document would be 3.75 x 4.25.
As a general guideline, use margins of at least 1/8 to 1/4 of an inch to avoid having text or images cut off unintentionally in the printing and cutting process.
Countries that use ISO paper sizes may use A8 (74 × 52 mm) or ID-1 ( approx. 85.60 × 53.98 mm or 3.370 × 2.125 in) for standard business cards. But no matter what the standard is in your country you aren't obligated to use standard size business cards.
Non-Standard Business Card Sizes
"Business cards designs in these modern times are abundant and unique, one of the surefire ways to attract even more attention with your business card is to choose a nonstandard business card size. Unusual business card sizes and shapes and the attention they attract is almost always worth the extra few dollars that you will spend on odd-shaped cards." Tiny Prints Read more about business card size.
...refreshing to do something outside of a common template, but... QBN Read more about why you may or may not want to go with standard size business cards.

