3DPrintCalcs
Filament Length Calculator — Metres per Spool
Calculate the total length of filament on a spool from its weight, diameter and material density.
How We Calculate This
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.
Frequently Asked Questions
A 1kg spool of 1.75mm PLA contains approximately 335 metres. The exact length varies by material density — PETG gives about 327m and ABS about 400m per kilogram.
Yes, significantly. 2.85mm filament has about 2.65 times the cross-sectional area of 1.75mm filament, so the same weight gives roughly 2.65 times less length.
Different materials have different densities. Less dense materials like ABS produce more length per kilogram than denser materials like PLA, because the same mass occupies more volume.
The calculation is mathematically exact for perfectly round filament. Real-world filament may vary by 1-3% due to manufacturing tolerances in diameter and density.
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Spool Life Calculator
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Filament Diameter Calculator
Calculate cross-sectional area and volume per metre for any filament diameter.
Multi-Colour Print Calculator
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Last updated: February 2026
All calculations are estimates. Always verify settings with test prints before committing to final prints.