For the common case — 1.75 mm PLA — 2.98 g. But the figure is a property of the material, and the spread across materials is more than three to one.
| Filament | Density | 1.75 mm | 2.85 mm |
|---|---|---|---|
| Polypropylene | 0.9 g/cm³ | 2.16 g/m | — |
| ABS | 1.05 | 2.53 g/m | 6.7 g/m |
| PA6 | 1.14 | 2.74 g/m | — |
| TPU 95A | 1.2 | 2.89 g/m | — |
| PLA | 1.24 | 2.98 g/m | 7.91 g/m |
| PETG | 1.27 | 3.05 g/m | 8.1 g/m |
| Metal-filled PLA | 3.2 | 7.7 g/m | — |
Where the number comes from
Two things and nothing else: cross-sectional area and density. A 1.75 mm filament has an area of 2.405 mm², so a metre of it is 2,405 cubic millimetres of plastic. Multiply that volume by the density and you have the mass.
That is why no brand-specific figure exists and why none is needed. Two spools of the same polymer at the same diameter weigh the same per metre, whatever the label says.
What it is actually for
Estimating what is left without unwinding anything. If you can measure or estimate the length still on a reel, grams per metre converts it straight into mass, and mass converts into prints.
It also works in reverse, which is the more common direction: a slicer that says a part needs 60 g of PLA is asking for roughly twenty metres of 1.75 mm filament.
The extremes are worth looking at
Polypropylene at 0.9 g/cm³ and metal-filled PLA at 3.2 sit at opposite ends of the table, and the ratio between them is three and a half to one. A metre of the first weighs less than a third of what a metre of the second does.
That is the practical meaning of density on a spool: two reels of the same nominal kilogram, wound to wildly different diameters, holding wildly different amounts of printable object. Nothing about the packaging tells you which you have — only the material does.
The 2.85 mm column is not double
A 2.85 mm filament has 6.3794 mm² of cross-section against 2.405, so it weighs 2.65 times as much per metre — not 1.63 times as the diameter ratio would suggest. Area goes with the square of diameter, which catches people out every time they switch machines.
Any combination you like — 1.75 or 2.85, any polymer's density — goes into the length and weight converter. If you need to look a density up first, the materials index has all thirty-five.