Filament spool calculator: how much is left
Weigh the spool, or enter the length left, to see the grams and meters remaining and how many more prints you can start.
Working it out…
How this is worked out
Filament is a thin cylinder of plastic, so its weight and its length are tied together by its thickness and its density. Weigh the spool and subtract the empty spool to get the filament left; or, if you know the length, multiply it by the weight of one meter.
Grams per meter = π × (diameter in mm)² ÷ 4 × density in g/cm³
Filament left (g) = weight of spool and filament − weight of empty spool, or length in m × grams per meter
Length left (m) = filament left ÷ grams per meter
Prints left = filament left ÷ filament per print, rounded down
A square millimeter of filament over one meter is exactly one cubic centimeter, which is why density in g/cm³ gives grams per meter directly.
Assumptions
- The density presets are from the makers' data sheets. Other brands, colors and fillers differ a little, so the length is a close estimate, not exact.
- The empty spool weight, the scale reading, the length and the filament per print are examples, not research. The weight of an empty spool varies by brand, so weigh your own.
- The diameter is taken as exact. Real filament varies by a few hundredths of a millimeter.
- Prints left counts whole prints from the filament that is on the spool. Filament lost to a spool change or a color purge is not counted; see the purge waste calculator.
Preset figures and where they come from
Each figure was read on the company’s own page, checked on 15 November 2026.
| Preset | Figure | Source |
|---|---|---|
| Bambu Lab PLA Basic | 1.24 g/cm³ | cdn.shopify.com |
| Polymaker PolyTerra PLA | 1.31 g/cm³ | polymaker.com |
| Polymaker PolyLite PLA | 1.17 g/cm³ | wiki.polymaker.com |
Every preset is only a starting value. Change any field if your account, country or plan differs.
Questions sellers ask
How do I know how much filament is left on a spool?
Weigh the spool on a kitchen scale and subtract the weight of an empty spool of the same brand. With the example figures, 640 g on the scale less a 250 g empty spool leaves 390 g, which is 39% of a 1000 g spool and about 130.8 m of 1.75 mm filament.
How many meters of filament are on a 1 kg spool?
It depends on the plastic. For Bambu Lab PLA Basic at 1.24 g/cm³ and 1.75 mm, a 1 kg spool holds about 335 m. A denser filament gives fewer meters for the same weight, and 2.85 mm filament gives far fewer.
Will my spool finish the print?
Check the filament left against what the print needs, with a little to spare. A 45 g print needs about 15.1 m of 1.75 mm PLA, so the 390 g left in the example makes 8 more of them with 30 g over. Do not start a long print on a spool that has less than the slicer says it needs.
Why does my weight not match the length on the spool?
Because spools and fillers differ. The label gives the length for its own material and diameter. If the weight and the length disagree, enter your density and diameter by choosing "My own figures" in the filament list, and weigh the empty spool again.