Planning guide

How to Calculate Filament Left on a Spool

How much usable material remains after a spool has been opened?

Work through the process

1. Place the spool on a level scale and record its gross weight.
2. Find the empty weight for that exact spool, including its hub.
3. Subtract the empty weight and convert the net mass if length is useful.

Formula and worked illustration

A 680 g spool with a 220 g empty carrier contains 460 g of filament. At 1.75 mm and 1.24 g/cm³ that corresponds to about 154.2 m.

Inputs and limits

A guessed tare can dominate the error. A cardboard spool may change weight with moisture; avoid assuming every carrier from one brand has the same tare.

Use the Spool Remaining Calculator to change the assumptions and compare your own inputs. Examples here are illustrative calculations, not results from a physical print test.