Filament Length Calculator

Frequently Asked Questions

How is filament length converted from weight?

Length (m) = weight (g) ÷ (π × (d/2)² × density × 100), where d is filament diameter in cm. For 1.75 mm PLA (1.24 g/cm³): 1 kg ≈ 335 m; for 2.85 mm PLA: 1 kg ≈ 126 m.

Quick reference for common materials?

Per 1 kg of 1.75 mm filament: PLA ≈ 335 m, PETG ≈ 327 m, ABS ≈ 400 m, TPU 95A ≈ 343 m. Switch to 2.85 mm and lengths drop to ≈38% of the 1.75 mm values.

Why does diameter matter so much?

Filament volume scales with the square of diameter: 2.85 mm has (2.85/1.75)² ≈ 2.65× the cross-section of 1.75 mm. The same kg therefore stretches 2.65× shorter in the thicker filament.

How do I estimate remaining filament on a partial spool?

Weigh the spool, subtract the empty-spool weight (often 200–300 g, printed on the box), then divide by g/m for your filament. 1.75 mm PLA is ≈3.0 g/m, so 600 g of net filament ≈ 200 m.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Filament is sold by mass (grams or kilograms) but used by length (meters as the printer pulls it through the extruder). Converting between the two only needs three numbers: filament diameter (1.75 or 2.85 mm are the global standards), material density (g/cm³), and either the weight or the length you want to convert. The calculator computes a constant - grams per meter for that diameter and material - and then divides or multiplies. Use it to plan whether a partly-used spool has enough plastic for a long print, to estimate how many meters a 250 g sample contains, or to translate a slicer's length output into the cost of the spool you are about to deplete.

Formula / Method

Filament cross-sectional area A = π × (d ÷ 2)², with d in mm. Mass per unit length (g/m) = A (mm²) × 1 m (= 1000 mm) × density (g/cm³) ÷ 1000 (mm³ per cm³) = π × (d ÷ 2)² × density. Then length (m) = weight (g) ÷ (g/m), and inversely weight (g) = length (m) × (g/m). Standard densities: PLA 1.24, PETG 1.27, ABS 1.04, TPU 1.21, Nylon 1.14, ASA 1.07, PC 1.20 g/cm³. Carbon-fiber and metal-filled blends can run 1.3–3.0 g/cm³; always check the spool data sheet for filled materials.

Worked Example

A 1.75 mm PLA filament: cross-section = π × (0.875)² ≈ 2.405 mm². Grams per meter = 2.405 × 1.24 ≈ 2.98 g/m. A 1 kg spool therefore holds about 1000 ÷ 2.98 ≈ 335 m of filament, which matches the "~330 m" figure printed on most PLA spools. A 250 g sample is about 83 m. For 2.85 mm PLA the area is 2.71× larger, so grams per meter rise to about 7.92 and a 1 kg spool yields only about 126 m. PETG at 1.27 in 1.75 mm is about 3.05 g/m - only 2.4% different from PLA per meter, despite the higher density, because diameter dominates.

Common Mistakes

Mixing up filament diameter (1.75 vs 2.85 mm) - the cross-section ratio is 2.65×, so a 2.85 spool of the same mass is far shorter than a 1.75 spool.

Using PLA density for everything - ABS is about 16% less dense, so a 1 kg ABS spool holds about 16% more length than a 1 kg PLA spool of the same diameter.

Ignoring actual diameter tolerance - cheap filament can vary ±0.05 mm, which is ±6% of cross-section and length.

Counting the cardboard core in the spool weight when measuring "remaining filament" on a kitchen scale; subtract the empty-spool tare.

Treating the slicer's "length used" line as the spool length consumed - purge towers, prime lines, and a partial start often add a few meters.

Tips & FAQ

How long is a typical 1 kg PLA spool? Around 330 m for 1.75 mm; 125 m for 2.85 mm. Why does diameter matter so much? Mass per meter scales with the square of diameter - doubling the diameter quadruples the per-meter mass. What about filled filaments? Carbon-fiber-PLA is around 1.30 g/cm³, metal-fill PLAs can reach 3.0+ - use the spool spec, not the base resin number. Can I weigh the spool to estimate remaining length? Yes - weigh, subtract the empty-spool tare (printed on most spools, typically 150–250 g), and convert. Do I need to account for moisture? Nylon and TPU absorb water and gain a percent or two of mass when wet; that is mass you cannot extrude (it bubbles out as steam), so dry first. How precise should density be? ±0.02 in density shifts length by under 2% - good enough for spool planning. Why is my actual usage higher than this estimate? Slicer estimates include purge, brim, support; this tool converts whatever weight or length you input. This is a planning estimate, not a measurement - always leave a margin when starting a print that uses nearly the whole spool.

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