📏 Filament Length From Weight Calculator
Estimate how many meters of filament are on a spool (or in a print) based on its weight, material density, and diameter.
Weight becomes volume, volume becomes length
Filament is a cylinder of known diameter, so length is just its volume divided by its cross-section. The tool converts the diameter to centimetres first, which is why every figure below is in cm:
volume (cm³) = weight (g) / density (g/cm³)
area (cm²) = π × (diameter / 20)²
length (m) = volume / area / 100Take the defaults: 1000 g of PLA at 1.24 g/cm³ is 806.45 cm³. A 1.75 mm strand has a radius of 0.0875 cm, so its area is π × 0.0875² = 0.024053 cm². Dividing gives 33,528 cm, or 335.3 m - the number printed on most PLA spools.
What each 1 kg spool gives you
Density is the only thing that changes between materials, and the drop-down carries the values the calculator actually uses:
| Material | Density | 1 kg at 1.75 mm | at 2.85 mm |
|---|---|---|---|
| PLA | 1.24 | 335.3 m | 126.4 m |
| PETG | 1.27 | 327.4 m | 123.4 m |
| ABS | 1.04 | 399.8 m | 150.7 m |
| TPU | 1.21 | 343.6 m | 129.5 m |
| Nylon | 1.30 | 319.8 m | 120.5 m |
Frequently asked questions
How many meters is 1 kg of PLA filament?
Roughly 335 m at 1.75 mm and 126 m at 2.85 mm. The thicker strand holds 2.65 times the plastic per metre, because area scales with the square of diameter.
How do I tell how much filament is left on a partly used spool?
Weigh the whole spool on a kitchen scale, subtract the empty reel weight stamped on the side, and enter the difference. 430 g of PLA left is about 144 m.
Why is my measured length shorter than the calculated one?
Filament diameter varies by around 0.02 mm either way even on good spools, and area follows the square, so a strand running 1.77 mm instead of 1.75 mm holds about 2.3% more plastic per metre and therefore fewer metres per kilo. Pigment loading, especially in metallics and glow filaments, also raises density above the nominal figure.