Planning guide

How Filament Diameter and Density Affect Length

Why do equal-weight spools contain different lengths?

Work through the process

1. Hold mass constant when comparing materials.
2. Change density while keeping diameter fixed.
3. Compare diameters only after updating the correct cross-sectional area.

Formula and worked illustration

Length varies inversely with density and with diameter squared. At 1.24 g/cm³, a 1000 g spool is about 335.28 m at 1.75 mm and 126.42 m at 2.85 mm.

Inputs and limits

Filled, foaming and blended filaments may differ substantially from generic reference densities. Use actual product information.

Use the Filament Weight & Length Converter to change the assumptions and compare your own inputs. Examples here are illustrative calculations, not results from a physical print test.