Convert filament between length and weight in either direction. Useful for estimating how much spool you have left, planning a print against remaining filament, or sanity-checking a slicer’s usage estimate.
How it works
Filament is a solid cylinder, so its weight follows directly from geometry and density.
area (cm²) = π × r² (r = diameter ÷ 2, in cm)
mass per meter (g/m) = area × 100 cm × density
For 1.75mm PLA: the radius is 0.0875 cm, so area = π × 0.0875² ≈ 0.02405 cm². At a
density of 1.24 g/cm³, each meter (100 cm) weighs 0.02405 × 100 × 1.24 ≈ 2.98 g.
From there:
- Length → Weight: weight = length (m) × mass per meter
- Weight → Length: length = weight (g) ÷ mass per meter
Why diameter dominates
Because area depends on r², weight scales with the square of the diameter. A 2.85mm strand has
about (2.85 ÷ 1.75)² ≈ 2.65× the cross-section of a 1.75mm strand, so the same length weighs
roughly 2.65 times as much. Always pick the correct diameter or the result can be off by more
than half.
Example: how much is left on a spool
You weigh a partly-used PLA spool at 540g. The empty spool weighs 210g, so 330g of filament
remains. Using Weight → Length for 1.75mm PLA (2.98 g/m), that is about 330 ÷ 2.98 ≈ 110 m
left — enough to plan your next few prints. Everything is computed locally in your browser.
Material density reference
Different filament materials have different densities, which directly affects the length-to-weight conversion. Here are the published datasheet values used by the calculator:
| Material | Density (g/cm³) | g/m at 1.75mm | g/m at 2.85mm |
|---|---|---|---|
| PLA | 1.24 | ~2.98 | ~7.90 |
| PETG | 1.27 | ~3.05 | ~8.10 |
| ABS | 1.04 | ~2.50 | ~6.63 |
| ASA | 1.07 | ~2.57 | ~6.83 |
| TPU | 1.21 | ~2.91 | ~7.71 |
| Nylon | 1.14 | ~2.74 | ~7.27 |
Real filament varies a few percent between brands and colorants, so use these as close estimates.
Practical applications
Checking before a print: Enter the length your slicer reports in the Length → Weight direction to find if the remaining grams on your spool are enough. A common mistake is relying on the slicer’s visual progress bar, which reports estimated length, not weight — the converter lets you compare the two directly.
Buying the right spool size: If your slicer says a part uses 85 m of 1.75mm PETG, the weight is roughly 85 × 3.05 ≈ 259 g. A 250g spool would not quite cover it; a 500g spool gives comfortable margin.
Empty-spool weights: Most manufacturers print the net filament weight (typically 1000g or 750g) on the label. Empty spool weights vary from about 140g for light cardboard spools to 250g or more for heavy plastic spools. Weighing the spool before and after a print gives the most accurate usage tracking.