Fold a sheet of paper in half? Child's play. Fold it in four? No problem. But to divide a sheet of paper into three neat and perfect parts? A real challenge. Anyone who has ever folded an important document will tell you: it is surprising how delicate this task requires. Whether it's a letter to your loved one, a project for math class, or a scrap sheet you've decided to divide into three equal parts, a perfectly fine sheet of paper. folded is proof of professionalism and attention to detail.
Steps
Method 1 of 5: Use the "intuitive" technique
Step 1. Start by laying your sheet of paper flat on your work surface
Believe it or not, there are many ways to fold a sheet of paper into thirds, but some techniques give more accurate results than others. Try this method if you don't need to be precise is a fast and efficient method, but the results obtained are rarely perfect.
 The good part is that you don't need any instruments for this method.
 Note that it is not necessary to perfectly fold a standard 22 × 28 cm sheet of paper to fit it into an envelope. It is therefore a good choice of dimension for correspondence.
Step 2. Roll up the paper to form a large cylinder
Your goal is to get a large loose roll from your sheet of paper, it should be roughly the size of a newspaper rolled up on itself. Don't make any folds yet.
Step 3. Line up the edges before gently flattening the center
Look at your cylinder from the side, one edge of the rolled up paper should be on the left and the other edge should be directly on the other side, on the right. Start compressing the cylinder, adjusting as you go to line up the edges.
The three layers of paper obtained should be approximately the same size. To do this, you will need to make sure that one edge of the paper is snug against the inside of the folded cylinder and the other edge is placed just above, flush with the first fold. It's more intuitive than it sounds
Step 4. Completely flatten the cylinder when you are close to the desired result
When you see that your paper is almost perfectly folded into three equal parts, press the edges of the paper to get crisp, smooth creases. Congratulation ! Your sheet should now be (almost) perfectly divided into three equal parts.
From there you can make last minute adjustments, but avoid making more than one crease unless your three parts are really uneven  it will look less professional
Method 2 of 5: Use the "reference paper" technique
Step 1. Fold a sheet of “rough” paper into three roughly equal parts
This method involves sacrificing a sheet of paper to help you perfectly fold another sheet. You will need two sheets of paper for this method, one that you fold correctly and one that you are not afraid to waste. Your two sheets of paper should be the same size.
Fold your "rough" paper into three roughly equal parts using your technique of choice, you can use the "intuitive" method explained previously or one of the other methods described in this article. You can even go there groping to get correct folds
Step 2. Fold over until the lengths of all three parts are as precise as possible
Now adjust your scrap paper until it is folded into three almost perfectly equal parts.
Don't worry about how long it will take or how many times you need to fold or unfold, that sheet of paper doesn't “count”
Step 3. Use your scrap paper as a guide to fold the “right” sheet of paper
Once you're happy with the creases in your scrap paper, take the white sheet you just folded and line up its edges with those of the paper you want to fold perfectly. Use scrap paper as a pattern to make the folds of your "good" sheet of paper.
You can do this by marking the positions of the folds on the “correct” sheet of paper or trying to visually compare the two sheets
Step 4. If you want, use an object with a straight border
If you wish, you can take an object with a straight border (like something as simple as an envelope) and lay it on both sheets to help you mark the folds of your scrap paper on your "good." " sheet of paper. If you are using an object with a solid rectilinear border, you can even fold your "good" sheet of paper against that border for more precision.
When you are finished, save your “scrap” paper for future notes or recycle it. Do not throw away an undamaged sheet of paper
Method 3 of 5: Use the "at sight" technique
Step 1. Fold the edges of the sheet of paper over it
This method results in three parts of perfectly equal lengths and requires nothing more than the measuring power of the human eye to find the points where the sheet bends into three parts. Surprisingly, this method is effective. In fact, once you've worked out a few times, you can probably get away with using it for important mail.
To start, take a border of the sheet and fold it over the rest of the paper to double it. Don't make any folds right away  your sheet should be gently rounded
Step 2. Align the border so that it covers half of the space on the sheet
Try to line up the edge of the paper you are folding, so that it covers half of the space of the remaining sheet. The human eye judges halves better than thirds, which is why it will be much easier to align the paper correctly this way than if you had tried to align the threepart paper from the start.
When the edges of the paper are perfectly aligned, fold the paper, making sure that the free edge does not move as you fold
Step 3. Slip the remaining border into the crease and fold it in half
The hardest part of this method is already done. Now all you have to do is fold the last third. To do this, take the other edge of the sheet of paper and tuck it under the top edge so that it fits snugly against the inside of the fold. Make a second fold.
If you made perfect creases, all the edges of your paper should now be aligned. If not, feel free to make minor adjustments if needed
Method 4 of 5: Use the "origami" technique
Step 1. Fold the paper in half
This method uses a technique derived from origami, the Japanese art of folding paper, in order to obtain three perfectly equal parts. Although origami is usually done with square sheets of paper, this method should also work with standard 22 × 28 cm sized paper, such as that typically found in offices. Start by folding your paper in half starting from the same border as if you wanted to fold the paper in three parts.

Remark:
if you don't want to make extra creases on your sheet of paper, you can find the middle of the sheet and carefully draw a line to separate the sheet in half. However, if you do this, your stroke should be extremely straight to match the crease line on a sheet of paper.
Step 2. Draw a line from the bottom left of the page to the right side of the middle fold
Position your sheet so that the fold you just made in the middle extends from your left to your right. Use an object with a straight border to carefully draw a line from the bottom left to the point where the middle crease meets the edge of the paper.
You can also use this method with a line that extends from the right corner to the bottom of the sheet, provided that you reverse the direction of all the indications from this point, but for practical reasons we have decided not to give the indications that to work in one direction
Step 3. Draw a line from the top left of the sheet to the bottom right
Use the right border of your object to carefully draw a line from the top left corner of the paper to the bottom of the right paper. This line should meet your middle crease in its center and your first line somewhere to the right of the page.
Step 4. Make a fold at the intersection of your two lines
The point where your two lines intersect marks one of the folds you need to make to divide the sheet into thirds. Use the right border of an object to draw a line that crosses that point and joins the two edges of the paper at a 90 ° angle.

Fold carefully along this border.
The folded corner should divide the rest of the paper into two halves, if it doesn't, you may need to adjust slightly at this point for it to be.
Step 5. Make the second fold by sliding the other side of the paper under the folded border
Finally, take the unfolded border of the paper and slide it under the folded border. Once it's snug against the inside of your first fold, make a second fold. Your paper should now be divided into three parts.
Method 5 of 5: Fold using math
Step 1. Measure the length of one side
If the previous methods weren't precise enough for you, try the next steps. You should then obtain folds which will be as precise as you can reasonably expect. You will need a measuring tool (such as a ruler) and a calculator or scrap sheet for this method. Start by measuring the length of the side along which you want to make the folds.
Step 2. Divide this length by three
By doing this you will get the length of each of your three parts.
 For example, if you are using a standard sheet of paper with dimensions of 22 × 28 cm and you want to divide this sheet into three equal parts along the border measuring 28 cm, simply divide 28 by 3; 28/3 = 9 and 1/3 or 9, 3. This means that the folds should be 9.3 cm apart from each other.
Step 3. Make a mark this distance from the edge of the paper
Using your measuring tool, mark the spot that corresponds to the distance determined above from the edge of the paper. Again, remember that your measurement should be taken along the edge you wish to fold.
In the example above, with the dimensions 22 × 28cm, we should have measured 9.3cm along the border measuring 28cm and made a mark at that distance
Step 4. Make a crease at this mark, then fold the flap over the sheet of paper
Make a fold at your mark, it should be perpendicular to both edges of the paper. This is the first of your two folds. The second will be easy to make  just slide the other side of the paper under the first flap so that it is snug against the inside of the first fold (just like the previous methods).
Advice
 Try to fold rather quickly for peace of mind. You don't need to try to get something too perfect. If you focus too much on getting perfect folds, you're probably more likely to mess up. Relax and do with what you have.
 If you have trouble making even folds, hold the corners of the part of the sheet you are folding over the rest of the sheet before you start folding the page, to simulate the fold before marking it. Make sure the two corners are perfectly aligned with the edge of the paper.
 When using the intuitive method, try to mold the shape of the cylinder so that it is more uniform. If the cylinder is a bit offset, you can increase or decrease the distance of the bend in order to get the most accurate result possible.