Filament Remaining Calculator
Find out how many metres of filament are left on a partly used spool by weighing it. Enter the net filament weight (spool weight minus the empty-spool weight), the filament diameter and the material density, and the tool converts weight to length so you know whether your next print will finish.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Weigh the spool on a kitchen scale and subtract the empty-spool weight to get the net filament weight in grams; enter that figure.
- Confirm the filament diameter (1.75 mm for most printers, 2.85 mm for some) and the material density (default 1.24 for PLA).
- Optionally enter how much filament your print needs (in metres, from your slicer) to see the spare left over and a will-it-finish check.
How it works
Weight is converted to volume by dividing by the material density (volume in cm³ = weight in g ÷ density in g/cm³). The filament is a long cylinder, so its cross-section area in cm² is π/4 × (diameter/10)² with the diameter converted from mm to cm. Length in cm is volume divided by area, then divided by 100 to give metres. If a required length is supplied, remaining minus required gives the spare and the pass/fail verdict.
Worked example
Worked example. A spool with 500 g of PLA left (1.75 mm, density 1.24 g/cm³): volume = 500 / 1.24 = 403.23 cm³; area = π/4 × 0.175² = 0.02405 cm²; length = 403.23 / 0.02405 = 16,764 cm = 167.64 m. If a print needs 120 m, the spare is 47.64 m — it finishes.
Common mistakes
- Forgetting to subtract the empty-spool weight — cardboard and plastic spools weigh 100–250 g, which would otherwise be counted as filament.
- Leaving the density at PLA's 1.24 when printing PETG (≈1.27), ABS (≈1.04) or TPU (≈1.20); density scales the length directly.
- Entering the wrong diameter — a 2.85 mm filament has over 2.6× the cross-section of 1.75 mm, so the same weight is far shorter.
Frequently asked questions
How do I get the net filament weight?
Weigh the whole spool, then subtract the empty-spool (bare reel) weight printed on the manufacturer's spec or measured from a finished spool. The result is the filament-only weight to enter here.
How accurate is this?
The length is accurate if your weight, diameter and density are right. The main uncertainty is the empty-spool weight, which varies by brand. For a long, critical print, keep a safety margin rather than relying on a near-exact match.
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Tip: Enter any known values to calculate the remaining results.
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