Filament Length Calculator
How Far a Spool Will Actually Get You
Spools are sold by weight, but slicers and multi-color print planning often work in length — how many meters are needed for a job, or how many meters remain on a spool of known weight. Converting between the two requires knowing the filament's cross-sectional area and material density, since a gram of dense PETG takes up less length than a gram of lighter PLA at the same diameter.
The Formula
Length = Volume / (π × (Diameter / 2)²)
This is the direct inverse of the filament weight calculation: instead of starting from length to find weight, it starts from a known weight and works backward to length.
Where This Calculation Matters
- Estimating remaining spool length — weighing a partial spool and subtracting the empty spool weight gives filament weight, which converts directly to remaining length.
- Planning multi-color or multi-material prints — length-based swap points are common in multi-material slicer profiles.
- Comparing spool value across materials — two 1kg spools of different materials don't contain the same length of usable filament.
- Verifying a "meters remaining" spool sensor — some printers estimate remaining filament by weight; this checks that estimate against the physical length.
Length per Spool by Material (1.75mm filament)
| Material | Density | 250g spool | 1kg spool |
|---|---|---|---|
| PLA | 1.24 g/cm³ | 83.8 m | 335.3 m |
| ABS | 1.04 g/cm³ | 99.9 m | 399.8 m |
| PETG | 1.27 g/cm³ | 81.8 m | 327.4 m |
| Nylon | 1.21 g/cm³ | 85.9 m | 343.6 m |
| TPU | 1.21 g/cm³ | 85.9 m | 343.6 m |
Figures assume 1.75mm diameter filament; 2.85mm filament yields roughly 40% of the length for the same weight, since cross-sectional area scales with the square of diameter.
How to Use This Calculator
- Enter the filament weight in grams.
- Enter the filament diameter in millimeters (typically 1.75mm).
- Select a material from the density dropdown, or choose Custom Density.
- Select Calculate to get the filament length in meters.
Related Calculations
Run the reverse calculation with the Filament Weight Calculator, or estimate total material needed with the 3D Print Cost Calculator.