A2 and A3 are two paper sizes that are part of the international standard ISO A. These are common European paper sizes, but are rarely used in America. American paper sizes are similar to those of the ISO sizes, but have their own measurements and names. The A2 paper size, according to Prepressure.com, measures 16.54 by 23.39 inches (420 x 594mm), and is often used to print posters or diagrams. A3 is smaller than A2, measuring 11.69 by 16.54 inches (297 x 420mm). The American alternative is called Tabloid, measuring 11 by 17 inches. A3 paper is regularly used for spreads, drawings and diagrams. You may want to convert A2 paper to A3 to make the next smallest paper size.
Lay the A2 paper out on a flat surface.
Fold the paper in half, bring its shortest sides together. When you do this, each of the two sides form an A3 size page. This is because all ISO A paper sizes have a constant height to width ratio. You can always fold a piece in half, and you'll get the next size, from A0 to A7.
Crease the paper well.
Place the paper on a paper cutter (or use scissors if you don't have one). Cut along the fold you just made. Now you have two pieces of A3 paper.
You can double-check your work by making sure the dimension are correct after you fold the paper. The width for A3 should by 11.69 inches and the height should be 16.54 inches (same as the width for A2).