Filament length to weight converter by material

The formula

Filament is a long cylinder. Its weight is its volume times the plastic’s density:

mass (g) = density (g/cm³) × π × (diameter / 2)² × length

Put the diameter in millimeters and the length in meters and the unit factors cancel, so one meter of filament weighs:

grams per meter = density × π × diameter² / 4

Everything the calculator shows comes from that one number. Grams are meters times grams per meter. Meters are grams divided by grams per meter. A 1 kg spool holds 1,000 divided by grams per meter.

How do you convert filament length to weight?

Multiply the length in meters by the grams in one meter of that filament. For 1.75 mm PLA at 1.24 g/cm³, one meter weighs 2.98 g, so 20 m weighs 59.7 g. Grams per meter is density times π times the diameter squared, divided by four, with diameter in millimeters.

Worked example: 20 m of PLA

These are the calculator’s defaults.

1. Cross-section of 1.75 mm filament: π × 1.75² / 4 = 2.405 mm².
2. Grams per meter: 2.405 × 1.24 = 2.98 g/m. (A meter of that cross-section is 2.405 cm³ of plastic.)
3. Weight of 20 m: 20 × 2.98 = 59.7 g.
4. Length of a 1 kg spool: 1,000 / 2.98 = 335 m.

Your slicer usually prints this conversion in its print summary, but it uses whatever density sits in the filament profile. If the profile says 1.24 and your spool is ASA at 1.05, the gram figure comes out about 18% too high. Take the density from the spool’s own data sheet instead.

How many meters of filament are on a 1 kg spool?

About 335 m for 1.75 mm PLA and about 126 m for 2.85 mm PLA. The number depends on density: lighter plastics give more meters per kilogram, so a 1 kg spool of 1.75 mm ABS at 1.05 g/cm³ holds about 396 m. The table covers each preset in the calculator.

Material	Density (g/cm³)	1.75 mm, meters per kg	2.85 mm, meters per kg
PLA	1.24	335	126
PLA-CF	1.22	341	128
PETG	1.25	333	125
PETG-CF	1.25	333	125
ABS	1.05	396	149
ASA	1.05	396	149
HIPS	1.05	396	149
TPU 95A	1.22	341	128
Nylon PA6/66	1.12	371	140
Nylon PA6-CF	1.09	381	144
PC	1.20	346	131
PVA	1.27	327	123

A 2.85 mm strand has 2.65 times the cross-section of a 1.75 mm one, so it holds about 2.65 times fewer meters per kilogram. Some sellers label 2.85 mm filament as “3 mm”. Measure it with calipers and type the real diameter if the two disagree.

Filament density by material, with sources

Each preset comes from a manufacturer’s technical data sheet. Most sheets test density to ISO 1183, the standard method for plastics.

Material	Density (g/cm³)	Source
PLA	1.24	Bambu Lab PLA Basic data sheet
PLA-CF	1.22	Bambu Lab PLA-CF data sheet
PETG	1.25	Bambu Lab PETG Basic data sheet; Polymaker PolyLite PETG data sheet
PETG-CF	1.25	Bambu Lab PETG-CF data sheet
ABS	1.05	Bambu Lab ABS data sheet
ASA	1.05	Bambu Lab ASA data sheet
HIPS	1.05	Fillamentum HIPS Extrafill data sheet
TPU 95A	1.22	Bambu Lab TPU 95A HF data sheet
Nylon PA6/66	1.12	Polymaker PolyMide CoPA data sheet
Nylon PA6-CF	1.09	Bambu Lab PA6-CF data sheet
PC	1.20	Bambu Lab PC data sheet
PVA	1.27	Bambu Lab PVA data sheet

Why your spool may differ

Density belongs to the exact product, not the polymer family. Bambu Lab’s PETG Basic sheet lists 1.25 g/cm³, and the same maker’s PETG HF sheet lists 1.28. That 2.4% gap moves the result by 2.4%. Pigments, fillers and fibers all shift density, and nylon grades vary more than most.

PA12 has no preset because no data sheet for an unfilled PA12 filament could be checked. Pick “Other” and type the value from your spool’s sheet.

How do you convert filament grams to meters?

Divide the grams by the grams in one meter. For 2.85 mm PETG at 1.25 g/cm³, one meter weighs 7.97 g, so 250 g is 31.4 m. Use this direction when a slicer reports only grams, or to find how many meters a part-used spool still holds.

Worked example: 250 g of 2.85 mm PETG

Set the direction to weight to length, diameter to 2.85 mm and material to PETG.

1. Cross-section: π × 2.85² / 4 = 6.379 mm².
2. Grams per meter: 6.379 × 1.25 = 7.97 g/m.
3. Length: 250 / 7.97 = 31.4 m.

How can you tell if there is enough filament left on a spool?

Weigh the spool, subtract the weight of an empty spool of the same brand and size, and compare the rest with the grams the print needs. If the remainder is larger, the print fits. Leave a margin for purge lines and a failed first layer, since the slicer figure covers only the part.

Worked example: a part-used PLA spool

Say the slicer reports 20 m of 1.75 mm PLA for the next print (59.7 g). The spool reads 412 g on a kitchen scale. An empty spool from the same brand weighed 165 g.

1. Filament left: 412 − 165 = 247 g.
2. As length: 247 / 2.98 = 82.8 m.
3. Margin: 247 − 59.7 = 187 g to spare, about 62.8 m.

Empty spool weights vary between brands, spool materials and sizes, so the calculator leaves that field blank. The most reliable figure is one you weigh yourself. Keep an emptied spool from each brand you buy, weigh it once and write the number on its side.

When the spool falls short, the tool shows by how many grams and meters. Unless your printer can swap spools mid-print, a job that runs out part way usually wastes the filament already laid down. The print cost calculator puts a price on that filament.

How accurate is a length to weight conversion?

The math is exact, so the error comes from the inputs. Diameter matters most because weight scales with its square. Filament that measures 1.77 mm instead of 1.75 mm weighs 2.3% more per meter. Density adds a few percent more between brands, as the PETG example above shows.

To tighten the result:

• Measure the diameter with calipers in several places along a meter and use the average.
• Take density from the data sheet of the exact product, not a generic chart.
• For a spool check, weigh on a scale that reads to 1 g or finer.

For multi-color prints, count the purge and flush filament too, because the slicer’s per-part figure may leave it out. The multi-color waste calculator estimates that extra weight.