Filament Length Calculator — Metres per Spool

Formula

The calculator uses the relationship between mass, density, and volume:

• Volume = Weight / Density
• Cross-sectional area = pi x (diameter/2)^2
• Length = Volume / Cross-sectional area

The weight is divided by the material density to get total volume in cm3, then divided by the filament cross-sectional area to get length in centimetres, which is converted to metres.

Continuous-extrusion time

The optional time estimate is an idealised figure: it assumes the hotend never stops extruding. Filament is consumed far more slowly than the head moves, because only a thin bead is laid down. The volumetric flow rate equals layer height × line width × print speed (mm3/s), and the filament feed rate equals that flow divided by the filament's own cross-sectional area. Real prints take longer once travel moves, retractions, heating and infill gaps are added.

Diameter tolerance

Spools are sold by net weight, so the nominal-diameter length is the published figure (about 335 m for 1 kg of 1.75 mm PLA). Leave the tolerance at 0 for that headline value, or enter your measured deviation (e.g. +0.02 mm) to see how a slightly thicker or thinner filament changes the length.