I noticed that people were saying that you should measure the diameter of your filament and enter that value into your slicer software. I had seen various values for the diameter of the filament, so I decided that I should measure mine, which is nominally 3mm.

As I started to measure the diameter of my filament with a digital vernier caliper, I noticed that I was not getting regular values. They ranged from about 2.92 to 2.98. At first I thought it was my bad technique, then it dawned on me that filament is an extruded product. I began to take my measurements with more care and attention to where I was measuring. I found that if I measured the diameter from topside to bottom side, I consistently got values around 2.98mm. When I measured from side to side, the values were around 2.92mm. Then it dawned on me! The filament is not round. It is oval. I was measuring the major and minor diameters of an ellipse.

I took two sets of ten measurements from both directions and averaged them. I found that from top to bottom, the average diameter was 2.98mm, and from side to side it was 2.91mm.

Using these values, I calculated the area of the ellipse (pi * r1 * r2) to be 6.81 sq mm. A circular filament of 3mm has a cross-sectional area of 7.07 sq mm.
Then I calculated the radius of a circular filament with a cross-sectional area of 6.81 sq mm and found the diameter to be 2.94mm.

Why is this important?
When you load an object's *.stl file into a slicer program, one of the items of data you give the software is the diameter of the filament. From that diameter, the program calculates the amount of filament required to make the object. If you are doing printing for profit, then this figure is important to you for costing the job.

Using the nominal 3mm diameter under-estimates the amount of material required by approximately 4% compared a diameter of 2.94mm.

I do not have any nominal 1.75mm filament to test whether it is oval, too.

Old Man Emu