4 paper refers to a specific size within the ISO 216 standard, which defines paper sizes used internationally (except in North America). Here’s what A4 paper means:

1. Size Specifications

• Dimensions: A4 paper measures 210 millimeters (mm) by 297 millimeters (mm) or 21 centimeters (cm) by 29.7 centimeters (cm), which is approximately 8.27 inches by 11.69 inches.

2. ISO 216 Standard (a4 paper)

• ISO 216: The International Organization for Standardization (ISO) defines a system of paper sizes where each size in the A-series is a half of the next larger size. For example, A4 is half the size of A3 and twice the size of A5.

3. Common Uses

• Printing and Writing: A4 is the most commonly used paper size for documents, letters, and printing worldwide.
• Office and School Supplies: Standard size for notebooks, forms, and textbooks.

4. Aspect Ratio

• Aspect Ratio of √2: The A-series paper sizes are based on a consistent aspect ratio of 2\sqrt{2}2​ (approximately 1:1.414), which allows for easy scaling without changing the proportions. Folding an A4 sheet in half parallel to its shorter sides produces an A5 size.
• Paper size scale
• The A-series of paper sizes is intuitive and proportionate, with each size doubling in size as you move up the scale. For example, A3 paper is 29 cm by 42 cm, and A2 paper is 42 cm by 59.5 cm

5. Global Standardization

• Widely Used: A4 is the standard paper size in most countries around the world, making it a universal size for international communication, publishing, and documentation.

In summary, A4 paper is a standardized size that is widely used for various applications due to its practicality and ease of use in printing and document handling.