The formula
Filament is a long cylinder, so its volume is the cross-section area times length. Multiply by density for weight:
grams = π × (d/2)² × length(mm) ÷ 1000 × density
metres = grams ÷ density × 1000 ÷ (π × (d/2)²) ÷ 1000
For 1.75 mm filament the cross-section is 2.405 mm², so 1 m holds 2.405 cm³ — about 2.98 g of PLA.
Checking how much is left on a spool
Weigh the spool, subtract the empty spool weight (often 150–250 g for plastic, ~120 g for cardboard; check the manufacturer), then enter the remaining grams to see how many metres you have. Compare with your slicer's filament estimate before starting a long print.
FAQ
How many metres of filament are in 1 kg?
About 335 m of 1.75 mm PLA, 327 m of PETG and 399 m of ABS. For 2.85 mm filament it's about 126 m of PLA.
How much does 1 metre of PLA weigh?
About 2.98 g for 1.75 mm and 7.9 g for 2.85 mm.
Why does density matter?
Lighter materials like ABS give more metres per kilogram than denser ones like PETG. Use the density printed on your spool for best accuracy.
Is 3 mm filament the same as 2.85 mm?
Most “3 mm” filament is actually 2.85 mm. Use 2.85 unless your spool says otherwise.
Recommended gear
- Digital kitchen scale (0.1 g) — Weigh spools to see what is left; 0.1 g resolution is plenty.
- PLA filament, 1 kg (1.75 mm) — The default for most prints; buy a known brand with tight diameter tolerance.
- PETG filament, 1 kg — Tougher and more heat-resistant than PLA for functional parts.
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