B7 paper size is part of the B series of paper sizes defined by the International Organization for Standardization (ISO) 216 standard. B7 paper measures 88 mm by 125 mm, or approximately 3.5 inches by 4.9 inches.
The B series is based on the same aspect ratio as the A series, which is 1:√2, and each size is defined as the geometric mean of the sizes in the A series. This means that B7 paper is the geometric mean of A7 and A8 paper sizes.
B7 paper is typically used for small-format documents, such as business cards, small flyers, or pamphlets. It can also be used for notepads, invitations, and other similar applications. B7 paper is often considered convenient because of its compact size, making it easy to carry around in pockets or small bags.
Like other paper sizes in the B series, B7 paper offers a unique property for enlarging and reducing documents. The enlargement from A7 to B7 is the same as the reduction from B7 to A8. This means that documents can easily be resized and printed without having to worry about changing the layout or aspect ratio.