A side bearing is the space outside a glyph’s outline, measured from the outline’s extreme points to the side of its body frame, and it controls the spacing to adjacent glyphs. In horizontally written scripts, each glyph has a left side bearing (LSB) and a right side bearing (RSB). Adjusting side bearings is essential for managing the overall rhythm and spacing of a typeface.

FONT ENGINEERING HINT

• Side bearing values are stored in the hmtx table for horizontal metrics.
• The advance width of a glyph is calculated as the sum of its glyph bounding box width, plus its left and right side bearings.