Why a Consistent Diameter is Important for 3D Printer Filament

When shopping for 3D printer filament, especially common types like PLA and ABS, you will find dimensional tolerances listed from each filament manufacturer. For example, Amazon Basics 1.75mm PLA filament has an advertised tolerance of +-0.5mm. This means that, at any given point along the filament spools, the diameter of the filament could be as large as 1.80mm or as small as 1.70mm.

You may also notice, if you analyze your filament options, that the tighter the dimensional tolerances are, the more expensive the filament tends to be.

But why is it important to have filament with a highly consistent diameter? Why would you pay a premium for filament just for a 0.03mm advantage in its tolerance? Let’s do the math.

Calculating the Amount of Filament your Printer Uses

The issue with filament manufacturers advertising the dimensional tolerance of their filament is that it obscures the information that is actually important for you as a 3D printer operator. The diameter of the filament is only indirectly important. What matters is the cross-sectional area of the filament because this determines how much plastic your 3D printer is using.

Filament with a diameter of exactly 1.75mm has a cross-sectional area of 2.4mm².

For a filament like Amazon Basics, at a diameter of up to 1.80mm, has a cross-sectional area of up to 2.54mm2.

So, while the diameter of the filament is only 2.8% higher than the nominal diameter, the cross-sectional area is about 6% greater. Therefore, the difference between the cross-sectional area at the maximum and minimum filament diameters for a filament with a tolerance of +-0.05mm is around 12%.

The controller inside your 3D printer assumes that the diameter of your filament is perfectly consistent. So, with Amazon Basics filament*, the amount of plastic your printer is actually extruding may be up to 6% greater than the controller expects. For finely detailed prints, this can affect print quality.

Comparing Filament Brands

So, we’ve established that dimensional consistency is important for 3D printer filament, as long as you are attempting to maximize the quality of your prints. The table below lists a bunch of the most popular brands of PLA filament along with their dimensional consistency, along with the corresponding consistency in their cross-sectional areas.