How Long Is 1 kg of PLA Filament?

by | Mar 23, 2021

3D printing filament is sold in spools classified by weight. They are often in 500-gram or 1-kilogram spools, although there are both bigger and smaller options. This is likely the most convenient unit of measurement in terms of sales and logistics.

Unfortunately, it’s easier to estimate how long a spool would last if you knew exactly how long the filament is. Here is a handy way to calculate for the meters of filament in your spool given its weight.

How to Calculate The Length?

Calculating the meters of filament in a spool requires only basic math. However, there are some values that you need to know beforehand. To make this demonstration easier to understand, let’s assign values based on a theoretical spool of 1.75-mm PLA filament.
Needed values:
W, Weight of the filament = 1 kilogram or 1000 grams
D, density of the filament = 1.25 grams / cm3 (for PLA)
F, diameter of the filament = 1.75 mm or 0.175 cm
A, cross-sectional area of the filament = Π * (F/2)2
= 3.14 * (0.175/2 cm)2
= 0.024 cm2
V, volume of the filament = W / D
= 1000 grams / 1.25 grams/cm3
= 800 cm3
L, length of the filament = V / A
= 800 cm3 / 0.024 cm2
= 33,333 cm or 333.3 meters
Based on our calculations, there are around 333 meters of filament in a 1-kilogram spool of PLA filament with a diameter of 1.75 millimeters. Take note that these calculations assume that the diameter of the filament is perfectly consistent throughout its length.

This approach may be used for any type of filament or spool SKU. You can also use the same calculations to estimate the length of leftover filament in a spool that has been partially consumed if you have a weighing scale at home. Just make sure to account for the weight of the empty spool.

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