WHY A4 PAPER DESIGNED AS 297mm×210mm?
The size of A4 paper (297 mm × 210 mm) is not random—it comes from a very clever mathematical design based on a special aspect ratio.
The Key Idea: Constant Proportion
All A-series paper sizes (A0, A1, A2, A3, A4, etc.) are designed using the same ratio:
Length : Width = √2 : 1
This ratio (approximately 1.414 : 1) has a unique property:
●When you cut a sheet in half parallel to its shorter side, the new sheet keeps the same proportions.
📄 How A4 Comes from A0
The system starts with A0, which has an area of exactly 1 square metre.
Each next size is made by folding/cutting the previous one in half:
Size: A0
Dimensions: 1189mm × 841mm
Size: A1
Dimensions: 841mm × 594mm
Size: A2
Dimensions: 594mm × 420mm
Size: A3
Dimensions: 420mm × 297mm
Size: A4
Dimensions: 297mm × 210mm
So, A4 is simply A0 folded 4 times.
✂️ Why √2 Ratio is Useful
This design makes paper extremely practical:
✔️ Scaling: You can enlarge or reduce documents without changing proportions
✔️ Photocopying: A4 → A3 or A5 → A4 works perfectly
✔️ No distortion: Content remains properly aligned
📘 Standardisation
The A-series system is defined by the international standard:
●ISO 216 paper size standard (ISO - International Organisation for Standardisation)
This standard is used worldwide (including India), except in a few countries like the US.
In Simple Words
A4 is 297 × 210 mm because:
●It follows the √2 ratio
●It is part of a system where each size is half of the previous
