# How long is a spool of filament?

Spools are sold by mass, not by length, so determining exact length of each spool is not possible. However, we can estimate how long a spool of filament is based on the type and its diameter.

Here's a chart of common filaments and their densities:

 Filament Type Density (g/cm^3) PLA 1.24 ABS 1.03 PET/PETG/PET+/ColorFabb XT 1.27 TPU 1.20 Flexible PLA 1.26 ColorFabb nGen 1.20 TPE (e.g. NinjaFlex, SemiFlex) 1.20 bronzeFill, copperFill, brassFill, steelFill 3.90 woodFill 1.15 GMASS Tungsten Metal ABS 4.00 Nylon 1.15 NylonX 1.00 Ryno 1.27

Once we have the density, we need the mass of the spool and the diameter of the filament. For this example we have a 1 kg spool of ABS that is 1.75 mm in diameter.

Here's the formula:

Length (m) = ( Mass (g) / Density (g/cm3) ) / ( π (3.14159) * (Diameter (mm) / 2))

So for our example, the equation would be:

Length (m)    =    ( 1000    /             1.04 )        / ( π (3.14159) *          (1.75 / 2) 2 )

Length (m)  ~= 400

Length (ft) = Length (m) * 3.28084, so

Length (ft) = 1312