3D Printer Filament Spool Length Calculator

How filament length is calculated

Filament is sold by weight (typically 1 kg spools), but slicers often report usage in meters or grams. Knowing how much length remains on a partial spool helps you plan prints and avoid running out mid-job.

The formula

The cross-section of a filament strand is a circle with area = π × (d/2)². Multiplied by the length and the material density, this gives the total mass. Rearranging to solve for length:

Length (mm) = Mass (g) / (π × (diameter/2)² × density)

Where:

• Mass is the weight of filament only (subtract spool weight if weighing the full spool)
• Diameter is the filament diameter (1.75 mm or 2.85 mm)
• Density varies by material (see below)

Material densities used in this calculator

Practical tip: tare your scale

Most empty spools weigh 200–250 g for 1 kg spools. Place the full spool on a kitchen scale, note the total weight, then subtract the known empty spool weight to get the filament-only mass. Many manufacturers print the spool weight on the label or packaging.

Standard spool lengths for reference

A full 1 kg spool of 1.75 mm PLA contains approximately 335 meters (1,100 feet). A full 1 kg spool of 2.85 mm PLA contains approximately 125 meters (410 feet). PETG spools are slightly shorter due to higher density; ABS and TPU run slightly longer because they are less dense than PLA.

About the print-time estimate

The hours figure in the result is deliberately a range, because filament consumption per hour varies more than any other number on this page. It works from 25 to 60 grams an hour, which covers most of what a desktop FDM machine does: a plate of small parts with lots of perimeters and travel sits near the bottom, a single large vase-mode print with a 0.6 mm nozzle near the top. Our filament cost calculator uses 45 g/hr as its single mid-range figure, which lands inside that band. Do not use it for scheduling. Slice the model and read the number your slicer gives you, since it knows the actual toolpath and this page only knows a mass.