Download Bambu Studio and slice some multi material prints. The preview tells you how much filament will be purged. There are several settings and model characteristics that will affect the purged volume.

Flushing volume: this directly controls the volume purged while swapping between any two filaments. Darker to lighter colors will need a higher flushing volume. You’ll also need a higher flushing volume when changing materials.

Purge to infill: this reduces the purged volume by accounting for the volume that can be printed as infill before reaching perimeters. It’s not very effective for smaller models because there is just less infill area.

Printing multiple copies: this reduces the ratio of waste to printed parts, since for each layer you’ll need the same number of filament swaps.

Part orientation: often the part orientation will have a dramatic effect on the number of filament swaps. Imagine a blue cube with a red face. This can be optimized to one color swap if the red face is horizontal instead of vertical.

Print sequentially: For multiple parts on the plate, grouping them by color similarity and printing groups sequentially can reduce the number of swaps. Imagine two blue parts and two red parts on the same plate. This can be optimized to one color swap for the entire print instead of one swap per layer.

In my experience, the waste for average complexity multicolor prints is similar in scale to supports, and is easily offset if you’re upgrading from a less reliable printer. Failed prints are filament waste too.