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
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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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Cite this tool
Zerdly. (2026). Filament Remaining Calculator. Retrieved from https://www.zerdly.com/tools/filament-remaining-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.