A3 size is a paper dimension that measures 11.7 x 16.5 inches or 297 x 420 millimeters. It is commonly used for printing documents, posters, and drawings. A3 is part of the ISO 216 standard, which defines various paper sizes based on the metric system. This size is often favored in design and art because it provides ample space for detailed work while remaining manageable. A3 paper can be easily folded to create A4 sheets, making it versatile for different applications, such as brochures and presentations.