A3 paper is a standard paper size that measures 11.7 x 16.5 inches or 297 x 420 millimeters. It is part of the ISO 216 standard, which defines various paper sizes used internationally. A3 paper is commonly used for printing large documents, posters, and drawings, providing ample space for detailed content. This paper size is often used in offices, schools, and design studios. It is larger than A4 paper, which measures 8.3 x 11.7 inches, making A3 a popular choice for presentations and creative projects that require more visual impact.