Weigh the spool, subtract the empty reel
The most reliable way to know what is left is a kitchen scale. Subtract the weight of the empty spool and you have the filament weight; divide by grams per meter for the length.
Filament left (g) = scale reading − empty spool
Meters left = grams left ÷ grams per meter (≈ 2.98 g/m for 1.75 mm PLA)
Typical empty spool weights
- Cardboard spools: about 120–160 g
- Plastic 1 kg spools: about 200–260 g
- Refills on reusable spools: weigh your own reel once and write it on it
The calculator adds a 5% safety margin before saying a print will fit, because slicer estimates are rarely exact and purge lines add a few grams.
Frequently asked questions
How much does an empty filament spool weigh?
Most plastic 1 kg spools weigh 200–260 g empty and cardboard spools 120–160 g. Weigh one of your brand to be sure.
Is there enough filament for my print?
Compare the grams left with the weight in your slicer plus about 5% for purge and skirt lines.