How to weigh a spool
- Put the whole spool on a kitchen scale and note the weight.
- Weigh an empty reel of the same brand once and keep the number. Many brands also list it.
- Enter both numbers above. The difference is the filament that is left.
The formula
filament left = weight on the scale − empty reel weightlength = filament left ÷ (density × filament cross-section)Worked example
A PLA spool weighs 420 g on the scale and the empty reel weighs 220 g. That leaves 200 g of filament, about 67 m of 1.75 mm PLA and 20% of a 1 kg spool. A 150 g print fits, with 50 g to spare.
Frequently asked questions
How do I know how much filament is left on a spool?
Put the spool on a kitchen scale, then subtract the weight of an empty reel of the same brand. What is left is the filament. The calculator also turns that into meters.
How much does an empty spool weigh?
It depends on the brand and the reel material. Plastic reels are often a couple of hundred grams, while cardboard reels are lighter. The reliable way is to weigh one empty reel from your brand once and reuse that number.
Is the remaining amount enough for my print?
Enter the filament your slicer needs for the print. The calculator compares it with what is left. Keep a small margin for purging, brims and supports.
Can I find the remaining length without a scale?
Only roughly, by measuring how thick the wound filament is on the reel. A scale is far more accurate and costs little.
Last updated: October 27, 2026
