About this tool
Filament Spool Remaining Length / Weight Calculator is a free, in-browser tool that tells you how much filament is still on a partial spool — in grams, metres and cubic centimetres — so you know whether a print will finish before you run out. Weigh the spool, or measure the wound coil, and it does the rest locally with nothing uploaded.
By weight, the remaining filament is gross weight now minus the empty (bare) spool weight; that mass converts to volume via the material density and to length via the strand cross-section π(d/2)² for 1.75 mm or 2.85 mm filament. By spool geometry, the wound ring's cross-sectional area is π(OD² − ID²) ÷ 4, multiplied by the coil width and a packing factor (~0.9 for the air between windings) to give the filament volume, then converted to length and weight the same way. Enter a full-spool net weight and it also shows the percentage remaining.
Use the weight method when you have a kitchen scale (most accurate) and the geometry method when you only have calipers. Densities used are PLA 1.24, ABS 1.04, PETG 1.27, TPU 1.21, Nylon 1.14 and ASA 1.07 g/cm³.