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Filament, weight and cost estimator

Converts between the three units nobody can convert between — the volume a slicer reports, the length a printer feeds, and the weight a spool is sold by — and works out what is left on a part-used spool from a set of kitchen scales.

The question this answers: “The slicer says 34 cm³. Is there enough left on this spool to finish it, and what is this print actually costing me?”

Your slicer reports this after slicing.

Sets the density. Override by picking the nearest if your supplier publishes a different figure.

The filament weight, not including the spool itself.

Result

Filament used
42.2 g
PLA at 1.24 g/cm³.
Length off the spool
14.14 m
Material cost
£0.93
At £22 per kg. Electricity and machine wear are not included.
Prints per full spool
23.7

Worth knowing about this answer

  • Density is taken as 1.24 g/cm³ for PLA. Manufacturers vary by a few per cent, and filled or effect filaments vary by more — if your supplier publishes a figure, use theirs.
  • The slicer’s volume figure excludes the priming line, purge blocks and anything wiped during a tool change. On a multi-colour print the purge can exceed the model itself.
Show the working
  1. Mass from volume34 cm³ × 1.24 g/cm³42.2 g
  2. Filament cross-sectionπ × (1.75 ÷ 2 ÷ 10)²0.0241 cm²
  3. Length34 ÷ 0.0241 ÷ 10014.14 m
  4. Price per kg£22 ÷ 1000 g × 1000£22

Filament used: 42.2 g. Length off the spool: 14.14 m. Material cost: £0.93. Prints per full spool: 23.7

How it works

Mass is volume multiplied by the material density. Length is volume divided by the filament’s cross-sectional area, which is π times the square of half the diameter. Cost is mass multiplied by the price per kilogram, derived from the spool price and its net weight. Remaining filament is the weighed spool less the empty spool, converted back to length through the same two constants.

What it assumes

  • Densities are nominal figures for the base polymer: PLA 1.24, PETG 1.27, ABS 1.04, ASA 1.07, TPU 1.21 and nylon 1.14 g/cm³. Real spools differ by a few per cent with pigment and formulation, and filled or effect filaments differ by more. The material is an input so a figure from your own supplier can replace ours.
  • Filament is treated as a perfect cylinder at its nominal diameter. Tolerance is typically ±0.02–0.05mm, which moves the length by a per cent or two and the mass not at all.
  • The slicer’s volume figure covers the model. Priming lines, purge blocks and tool-change waste are extra, and on a multi-colour print the purge can exceed the part.
  • Empty spool weights vary between brands and cardboard spools gain weight in a damp room. If you have never weighed an empty one of this brand, the remaining figure is approximate.

Where it stops being reliable

  • It says nothing about print time. Time depends on the slicer’s motion planning, the machine’s acceleration limits and the specific profile, and any estimate from volume alone would be confidently wrong. The slicer already knows.
  • Cost is material only. Electricity, failed prints, nozzle wear and your own time are all real and none of them are here.
  • It cannot tell you whether the print will succeed, which is the question behind “is there enough left”. A run-out is recoverable on a machine with filament detection and ruins the part on one without.

Runs entirely in your browser — nothing you type is sent anywhere. Last reviewed 2026-08-14. More on 3D printing.