Paper Folding Size Calculator
Calculate the resulting dimensions after folding paper.
Supports A4, A3, Letter, and custom sizes with multiple fold types.
Paper folding is fundamental to many crafts, from origami and card making to bookbinding and envelope creation. Understanding how paper dimensions change with each fold helps you plan projects accurately and choose the right starting paper size.
When you fold a piece of paper in half, one dimension is halved while the other stays the same. Which dimension gets halved depends on the fold direction. A horizontal fold (folding the top edge down to the bottom) halves the height. A vertical fold (folding the left edge to the right) halves the width. Each subsequent fold continues to halve one dimension.
Folding in thirds divides one dimension by three instead of two. This is commonly used for letter folds (fitting a letter into a standard envelope) and brochure layouts. A tri-fold brochure starts with a standard sheet and folds it into three equal panels.
Accordion folds (also called zigzag or fan folds) divide the paper into equal panels that alternate direction. An accordion fold into four panels divides one dimension by four. The resulting panel size is the same as if you had folded in half twice, but the paper zigzags rather than stacking.
Standard paper sizes used worldwide include the ISO A series (A4 is 210 by 297 mm, A3 is 297 by 420 mm) and the North American Letter size (8.5 by 11 inches, which equals 215.9 by 279.4 mm). The ISO A series has an elegant property: each size is exactly half of the next larger size, and all sizes maintain the same aspect ratio of 1 to the square root of 2.
For custom square paper (common in origami), the dimensions start equal and diverge with each fold. Traditional origami paper (kami) comes in standard sizes of 15 by 15 cm (about 6 by 6 inches) and 25 by 25 cm (about 10 by 10 inches).
There is a practical limit to how many times you can fold a piece of paper. Each fold doubles the thickness, and after about 6 to 7 folds, standard paper becomes too thick and stiff to fold further. Thinner paper can be folded more times. The theoretical maximum number of folds depends on paper thickness and length, described by the Britney Gallivan equation.
This calculator shows you the resulting dimensions after your specified number of folds, helping you plan your craft projects with precision.