How to Cut a Perfect Square From Letter or A4 Paper

Almost every origami diagram starts with a square, and almost every house only has rectangular printer paper. Learning how to cut a perfect square from a US Letter (8.5 x 11 in) or A4 sheet is a quick job, and there are three ways to do it depending on what you have on hand and how much precision the model demands.

Method 1: The Diagonal Fold, No Ruler

The fastest method, and the only one that works anywhere.

1. Lay the sheet in landscape orientation, long edges at the top and bottom.
2. Take the top-left corner and fold it down until the short left edge lies exactly along the bottom edge. The sheet now forms a triangle with a strip left over on the right.
3. Line it up carefully before you press: this alignment decides whether the square comes out true.
4. Crease the leftover strip by folding it over the triangle.
5. Cut along that crease with scissors, or crease it firmly and tear it against a ruler.

The short side of the sheet sets the size, so US Letter gives you an 8.5-inch (21.6 cm) square and A4 gives you a 21 cm (about 8.25-inch) square.

Method 2: Measure and Cut

When precision matters (models with many layers, boxes that have to fit together, modular pieces), measuring is more reliable.

1. Measure the short side of the sheet. On US Letter that is 8.5 inches; on A4 it is 21 cm.
2. Mark that same distance along both long sides, measuring from the same end.
3. Join the marks with a ruler and a light pencil line.
4. Cut with a craft knife held against the ruler, in a single pass. Several partial cuts leave a ragged edge.

This method also lets you cut smaller, identical squares, which is essential when you plan to fold many matching pieces.

Method 3: Two Squares From One Sheet

If the model calls for smaller paper, the same sheet yields two squares: 5.5 inches (14 cm) each from US Letter, or 14.8 cm each from A4. Both are close to the 6-inch (15 cm) standard most diagrams assume.

1. Cut the sheet in half across its length, making two rectangles of 8.5 x 5.5 inches (or 21 x 14.8 cm from A4).
2. Use the diagonal fold on each one, this time with the shorter side as your reference.

What to Do With the Leftover Strip

The strip that comes off the first method measures 8.5 x 2.5 inches on US Letter and 21 x 8.7 cm on A4. It does not have to go in the trash:

• Small squares (three of 2.5 inches from Letter, two of 8.5 cm from A4), good for tiny models or for practicing one specific fold.
• Strips about 3/8 inch (1 cm) wide for origami lucky stars. One sheet gives you a good handful of them.
• Reference strips for measuring other papers.

Checking That the Square Is Really Square

Fold it corner to corner along the diagonal. If the edges match with nothing sticking out in either direction, you are good. Being off by as little as 1/16 inch (a millimeter or two) is enough to leave a model visibly crooked at the end, because the error compounds with every fold.

This check matters most when you cut several squares in one go: it is common for the last one to come out different from the rest.

When Cutting Isn’t Worth It

Not every model needs a square. The paper boat and the paper hat start from rectangles, and forcing them into a square changes the proportions of the result. Check what the diagram asks for before you cut.

If you plan to fold often, at some point it pays to buy paper that is already cut. The comparison of the options is in the guide to the best origami paper.