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How To Resize an .STL File: The Complete Guide

STL files are versatile and easy to print on almost any 3D printer, but they can take up a lot of MB or even GB of space, making it difficult to share and upload your designs. However, there are several ways you can resize your file to make it smaller. 

To resize an .STL file: 

  1. Decrease the Resolution
  2. Adjust the Tolerance
  3. Use Binary STL Files
  4. Compress Your STL

So, let’s go through the steps and discuss how you can make your STL file smaller or larger. I’ll tell you how each step works and help you find the perfect size for your model so that you can save and print anything you can imagine!

1. Decrease the Resolution

Complicated, detailed STL files include upwards of thousands or millions of tiny triangles that make up the mesh of your design. These tiny images are what increase the resolution of your file to unmanageable levels.

When you save your STL file, you save multiple pieces of information about each triangle included in your design. For each triangle, the file format records: 

  • The coordinates of each vertex (v1, v2, and v3).
  • The direction of a “normal vector” that extends from the triangle’s center (to save the angle).

So, the more triangles in your design, the larger and the higher resolution your STL file will be. 

Adjusting the resolution of your STL can reduce its size while also removing unnecessary components of your design. 

When considering the resolution of an STL file, you are mainly looking at the number of triangles in your model. Generally, a good resolution STL includes 25,000 to 75,000 triangles, although smaller models may not require as many. 

Reducing the number of triangles will decrease the resolution, and as you lower it, the size of the file will also decrease. So, if you want your file to be smaller, you may want to reduce the number of triangles in your design. 

Finding a happy medium between a low-quality file and a huge, high-resolution file can be pretty challenging. However, if you mess around with the adjustments a bit, you can find the ideal amount of resolution and polygons for the amount of detail in your model. 

Most CAD programs have a feature that reduces the number of polygons in the file. That said, many use different names for the same feature (such as “decimation” and “reduce polygon percentage”). This means that you might have to do some research to figure out how to do it on your favorite CAD program.

You may also have to try adjusting the percentage of polygons a few times until you are pleased with the product. 

For an example of how to reduce the polygons in Meshmixer, check out this quick YouTube walkthrough from Callum Coles: 

2. Adjust the Tolerance

Tolerance, also known as chord height or deviation, represents the amount of error or deviation that you will allow from your 3D printer. In 3D printing, tolerance is usually measured in millimeters, and the measurement represents how much of your design you will sacrifice to preserve the integrity of your print. 

Since tolerance can remove some of the sharp details from the triangles in your STL file, it also reduces the file size of your model, helping you keep the amount of space it takes up to a minimum. 

For example, when your tolerance is higher, your printer may add more filament to certain areas of your model to make printing more manageable and increase your print’s strength. Your printer will print your 3D model exactly as represented in your STL file at the absolute lowest tolerance. 

Choosing the proper tolerance is crucial if you want the best end product. When dealing with STL files, you probably don’t want to see the sharp lines of every single triangle in your model, which is where raising your tolerance can make your print better. 

Generally, you want your file’s tolerance to be around 0.01 millimeters. This measurement means that your print takes up limited space, but it will also ensure that the print comes out with a smooth surface and just enough detail. 

3. Use Binary STL Files

There are two types of STL files, and one of them generally takes less storage space to save. 

STL file formats may use binary encoding or ASCII encoding to save information about the triangles in your design. 

ASCII STL files are far more detailed than binary STLs, which is both a blessing and a curse. ASCII-encoded STLs can get very large very quickly, especially if your model is highly detailed or has spherical parts that include tons of triangles. So, if you are tight on storage space, you might want to avoid ASCII STL files. 

Since ASCII can be so large, coders developed the more compact binary encoding for STL files to save space. Because the code for a binary STL file is far more compact and a bit less detailed, it is the way to save files that you want to be as small as possible. 

4. Compress Your STL

As with most files, compressing an STL is an excellent way to reduce the amount of storage space it takes. However, you should note that when working with 3D files such as STL (as opposed to 2D files), compressing your file will only make a slight difference. 

Ideally, compressing an STL file can reduce it by around 73%. However, sometimes this percentage will be much lower if you have tons of details to preserve. So, if you only need to shave off a few MB and don’t want to reduce the quality of your model, compression is the way to go. 

To compress an STL file, you can use programs or web apps like GZIP or 7-Zip

Final Thoughts

To resize an STL file, you can decrease the resolution of your model, adjust your file’s tolerance, save your file in binary STL, or compress your file. If you want your file to be larger and have more detail, you can do the exact opposite, increasing the number of polygons, reducing tolerance, and using ASCII encoding.