Best measurement method
Weight is usually the better estimate: weigh the current spool, then subtract the tare of an empty spool from the same brand, size, material, and revision. Do not assume every nominally similar spool has the same tare. Manufacturer designs change, and labels, adapters, RFID tags, or desiccant can add weight.
The Bambu reusable-spool reference comes from Bambu Lab's product specification, which lists 250 g. The dated MatterHackers references come from its empty spool weight table; its rows identify the spool year and approximate values. Filamentive reported a 250 g cross-brand average from a 2020 dataset and publishes a 205 g product-spool sheet. These are starting points only: overwrite the tare or save your own measurement.
Formulas
filament mass = gross spool weight − empty spool tarefilament area = π × (diameter ÷ 2)²length = (mass ÷ density) ÷ filament areageometry volume = π ÷ 4 × (wound OD² − core OD²) × wound width × packing factorsafe mass = mass × (1 − safety %) − fixed reserveThe calculator converts cubic centimetres to cubic millimetres before dividing volume by the filament cross-section. Geometry mode treats the wound pack as an annular cylinder and scales it by the entered packing factor. Real winding has gaps, ridges, and varying width, so that result is intentionally marked approximate.
Density and slicer limitations
Material presets are editable planning values, not specifications for every filament. Pigments, fillers, foaming, moisture, and formulation change density. Filled materials can differ sharply from their base polymer—use the density from the specific supplier's technical data when available.
A slicer's extrusion estimate is not the same as guaranteed spool consumption. Start/end purge, multi-material flushing, priming, failed starts, runout-sensor distance, and filament that cannot unwind from the hub may be missing. The percentage plus fixed reserve gives one conservative comparison, but it cannot eliminate those uncertainties.
Frequently asked questions
How many metres are in 1 kg of 1.75 mm PLA?
At the editable 1.24 g/cm³ preset, the ideal calculation is about 335 metres. A different actual diameter or density changes that result, and not all of it may be usable.
Can I use flange diameter for geometry mode?
No. Measure the outside diameter of the filament wound on the core. The spool flange contains no filament and would substantially overstate the estimate.
Does ToolQuill read my printer or slicer?
No. The calculator uses only values you enter. Saved tare profiles stay in local browser storage; nothing is uploaded or sent to a printer.