Filament diameter and density: two inputs that change the result

For the same length, theoretical mass depends on density and diameter squared. Spools of equal filament mass do not necessarily contain equal lengths. This is why inputs to the filament converter must match the product.

Separate four concepts

The interface uses density with g/cm³: it means mass per volume, not the proportion of material inside a printed part.

Read a specific product sheet

Prusament PLA sheet version 1.1 gives 1.75 ± 0.02 mm, with ± 0.03 mm for PLA Blend, and typical density 1.24 g/cm³, associated with ISO 1183. These values describe that product and document. They do not establish your spool’s dimensions or the density of every PLA filament.

Retain the full product name, formulation and consulted document. Do not copy the value for a filled variant or another reference simply because the base polymer shares a name. A typical value is an estimation input, not an individual measurement.

See the diameter-squared effect

Circular area is π × (d / 2)². Theoretical sensitivity example, with no spool measured: replacing 1.75 mm with 1.80 mm multiplies area by (1.80 / 1.75)² ≈ 1.057959, or +5.80%. At equal length and density, calculated mass changes by the same ratio.

This is not a claimed tolerance for the cited product. It demonstrates why a small diameter change does not cause a linear area change.

At fixed diameter and length, mass scales directly with density. Hypothetically replacing 1.24 with 1.30 g/cm³ gives 1.30 / 1.24 ≈ 1.048387, or +4.84%. These examples are independent; do not add them to describe a real spool.

Match precision to the inputs

Using nominal diameter and typical density produces a theoretical result. Two decimal places improve readability but do not create matching input accuracy. If you take your own measurements, record equipment, method, locations and limitations; one point does not describe an entire spool.

The mass-length guide explains units and both directions. This article explains input selection; it reports no diameter or density measurements performed by LayerBench3D.