Filament Swap Calculator — Multi-Colour Purge Waste

When you change filament colour mid-print, the old colour must be flushed out of the melt zone before the new colour prints cleanly. That flushed filament is deposited in a purge line, wipe tower or prime blob and becomes waste. A single swap typically purges roughly 50-300 mm of 1.75 mm filament (about 0.1-0.9 g of PLA), and a dark-to-light change purges far more than light-to-dark.

Use a purge-to-infill or purge-to-support strategy in your slicer so the flushed material is deposited inside the model rather than wasted in a separate wipe tower. Tune the per-transition purge volumes (a white-to-black change needs much less than black-to-white), order colours light-to-dark where possible, and keep a wipe tower only until your volumes are dialled in.

Yes. A manual M600 swap adds 20-60 seconds of pause-and-resume per change, and an automated multi-material unit (such as the Prusa MMU3, which now changes in roughly 40-50 seconds) adds the swap time plus the time to print the purge tower. Over dozens of changes this adds up considerably, which is why this calculator separates added swap time from base print time.

This calculator treats Purge Length as the length of raw filament consumed (extruded) per swap, which is how slicers report flushing volumes and the only model that gives realistic gram-scale waste. The mass is the round filament cross-section (pi x radius squared) times the length, converted to cm³, times the material density. A 120 mm purge of 1.75 mm PLA is about 0.36 g, not the few-milligram figure you would get from measuring the thin deposited bead.