Multi-color print waste calculator: purge, flush and cost

How to use this calculator

1. Slice the model with its colors assigned. Enter the filament change count from the print summary, or the layers that switch color and the changes on each.
2. Read the flush volume from the slicer’s flushing volumes table. With several color pairs, average them by how often each change happens.
3. Pick the material. The density fills in; overwrite it with your spool’s data sheet figure.
4. Enter the model’s own filament weight, the spool price and the purge tower weight.
5. Check the time fields against your printer profile.

The page link keeps every value you type.

The formula

changes         = slicer total, or layers with changes × changes per layer
filament area   = π × (diameter ÷ 2)²                          mm²
grams / change  = (flush mm³ + trimmed mm × area) × density ÷ 1000
flush waste     = changes × grams / change × (1 − share sent to infill or objects)
total waste     = flush waste + purge tower grams
waste share     = total waste ÷ (total waste + model grams)
added cost      = total waste × price per kg ÷ 1000
seconds/change  = unload and load seconds + flush mm³ ÷ max volumetric speed
added time      = changes × seconds/change

Density is in g/cm³ and one cubic centimeter is 1,000 mm³, which is why each volume is divided by 1,000 to give grams.

Where the defaults come from

Field	Default	Source
Flush volume	280 mm³	OrcaSlicer’s default purging volume between two different filaments, in PrintConfig.cpp
Density	1.24 g/cm³ (PLA)	OrcaSlicer’s PLA filament profile; PETG is 1.27 and ABS 1.04 in the same profile set
Unload and load time	57 s	OrcaSlicer’s Bambu Lab X1 Carbon profile: 28 s unload plus 29 s load inherited from the common machine profile
Max volumetric speed	12 mm³/s	OrcaSlicer’s PLA filament profile
Purge tower	0 g	Enter your slicer’s figure; the tower size depends on the model
Spool price	20 per kg	A round placeholder. Use your own receipt

Bambu Studio and OrcaSlicer calculate a flush volume for every color pair, so your own table will differ from the 280 mm³ default.

Worked example

Take a small figurine with 150 layers that each switch color once, printed in PLA. The model itself uses 50 g, and the spool cost 20 per kg. No purge tower weight is entered and no flush is redirected.

• Grams per change: 280 × 1.24 ÷ 1000 = 0.347 g
• Total waste: 150 × 0.347 = 52.1 g
• Waste share: 52.1 ÷ (52.1 + 50) = 51.0%
• Added cost: 52.1 × 20 ÷ 1000 = 1.04
• Filament cost: 2.04 multi-color, 1.00 single color
• Time per change: 57 + 280 ÷ 12 = 80.3 s, so 150 changes add 3 h 21 min

Why does multi-color printing waste so much filament?

A single-nozzle printer can hold only one filament at a time. At every color change, the old color still sits in the melt zone and nozzle, so the printer pushes new filament through until the extrudate runs clean. That flush is thrown away. A model with a color change on every layer repeats this hundreds of times.

The flush happens per change, not per model

Bambu Lab’s wiki describes the filament change as unload, flush, wipe and prime. The flushed plastic comes out beside the build plate and drops away from the print. On a single nozzle, the number of changes on a layer is usually one less than the number of filaments on that layer, because the next layer starts with the last color used.

The wiki’s own example shows the scale. A four-color test cube at 0.2 mm layer height needed 153 filament changes and produced 83 g of waste for an 11 g object.

Why owners call it poop

The flushed plastic lands in a chute as small coiled blobs, which owners call printer poop or filament poop. Each blob is one color change.

What is a purge tower?

A purge tower, also called a prime tower or wipe tower, is a sacrificial block printed beside the model. After each color change the nozzle prints a little of the new color onto it to settle flow and wipe off any remaining old color before returning to the part. It must rise as high as the last color change.

How big the tower gets

OrcaSlicer’s default prime volume is 45 mm³ per filament change, per its PrintConfig.cpp. The tower’s height is set by the highest layer that still has a change. Bambu Lab’s wiki shows a part whose tower used 14.76 g. Flipped upside down so the color changes sat near the bed, the same part needed a 9.05 g tower.

Prusa’s knowledge base notes that PrusaSlicer builds one wipe tower per plate however many objects share it, and varies its infill density layer by layer to waste as little filament as possible. Printing several copies at once spreads the tower across more parts.

How much filament does one color change waste?

At OrcaSlicer’s default purging volume of 280 mm³, one change flushes about 0.35 g of PLA. Real tables range much wider, because slicers set the volume per color pair. Bambu Lab’s four-color test cube averaged about 0.54 g per change including its prime tower: 83 g across 153 changes.

Converting flush volume to grams

Slicers state flush volume in mm³ because the extruder meters volume. Multiply by density and divide by 1,000:

Material	Density (OrcaSlicer profile)	150 mm³	280 mm³	500 mm³
PLA	1.24 g/cm³	0.19 g	0.35 g	0.62 g
PETG	1.27 g/cm³	0.19 g	0.36 g	0.64 g
ABS	1.04 g/cm³	0.16 g	0.29 g	0.52 g

Cut-off filament

On a Bambu Lab AMS (Automatic Material System) setup, the wiki explains that the filament left in the extruder and nozzle below the cutter’s cut is pushed out as part of the flush. That piece is already inside the flush volume, so the trim field defaults to 0 mm. Use it for waste the flush does not cover, such as a tip you snip off by hand during a manual swap. At 1.75 mm diameter, each 10 mm of trimmed PLA weighs about 0.03 g.

How much longer does a multi-color print take than a single-color print?

With the default profile values, each change adds about 80 seconds: 57 seconds to unload and load, plus about 23 seconds to flush 280 mm³ at 12 mm³/s. Across 150 changes that is 3 h 21 min. Whether that doubles or triples the print depends on how long the single-color model takes.

Where the time goes

Bambu Lab’s wiki notes that the flush runs at the filament’s max volumetric speed. A 0.2 mm nozzle flows less plastic per second, so flushing takes much longer than with a 0.4 mm nozzle. Unload and load times come from the printer profile: OrcaSlicer’s Bambu Lab X1 Carbon profile lists 28 s to unload, and its common machine profile lists 29 s to load.

Why some prints take three times as long

The added time depends on the change count, not on the size of the model. A small part with a change on every layer can spend more time changing color than printing. Take the worked example: if the 50 g figurine printed in 1 h 30 min in one color, the 3 h 21 min of changes bring it to about 4 h 51 min, a little over three times as long.

To estimate print time for a multi-color model, slice it and read the total. This calculator shows how much of that total the changes take.

What are flush volumes and how do you calibrate them?

Flush volumes are the mm³ of filament a slicer pushes through the nozzle to clear one color before the next. Bambu Studio and OrcaSlicer calculate a value for every from/to color pair. You calibrate them by lowering the multiplier or single table entries, printing a test and checking for tinted layers.

How slicers pick the numbers

Bambu Lab’s wiki says color is the main factor and material properties come second. OrcaSlicer’s source shows why dark to light costs more. In its fallback color formula, a pure black to pure white change scores 560 mm³ before the minimum flush is added, while white to black scores 80 mm³. Prusa’s knowledge base gives MMU (Multi-Material Unit) example values in the same direction: 150 mm³ from black to white and 50 mm³ from white to black. It adds that soluble supports and filaments with glitter or gloss additives usually need more purging.

Calibration steps

1. Slice the real model and note the total flush weight.
2. Open the flushing volumes table. In Bambu Studio the multiplier defaults to 1.00; 0.90 cuts every pair by 10%.
3. Lower the multiplier to 0.9 or 0.8, which Bambu Lab’s wiki suggests as a quick first saving, or edit only the pairs that change most often.
4. Print a small test that uses those color pairs, such as a striped block.
5. Look for discolored layers where one color meets the next. Tinted layers mean that pair needs more flush.
6. Raise the pairs that failed and keep the rest. The Re-calculate button in Bambu Studio restores the automatic values.

OrcaSlicer’s flushing dialog accepts multipliers from 0 to 3. Enter your calibrated average here to price the waste.

How do you reduce purge waste in multi-color printing?

Cut the number of changes first, then the waste per change. Print with a thicker layer height, orient the part so colors stack in bands, and put several copies on one plate. Then lower flush volumes after a test print and send the flush into infill, supports or sacrificial objects the slicer marks for it.

Fewer changes

Bambu Lab’s wiki gives measured examples. Raising the test cube from 0.2 mm to 0.28 mm layers cut changes from 153 to 111 and waste from 83 g to 61 g. Laying a tall part on its side cut changes and waste by almost 80% in another example. The same page warns that orientation can also backfire: a part with horizontal color bands went from 3 changes to far more when laid flat.

Printing copies together helps because waste depends on changes per layer, not on the number of parts. Nine copies of the cube produced the same 83 g of waste as one.

Order colors to minimize purge

Dark to light changes need the most flush. Bambu Studio’s automatic layer order starts each layer with the last filament of the layer below. It also picks the sequence with the smallest total flush, for example 1 to 3 to 2 over 1 to 2 to 3 when that is cheaper. You can set a custom order per layer range in Plate Settings. Where a design allows it, assign dark colors to the upper layers and light colors to the lower ones, so most transitions run light to dark.

Purge to infill vs purge to object

Both settings redirect flush into a printed part instead of the chute:

Setting	Where the flush goes	What to watch
Flush into objects’ infill	Hidden infill of the model	Light or transparent walls can show the mixed color; fewer walls make it more visible
Flush into objects’ support	Support that is removed later	On by default in Bambu Studio; saves little on models with small supports
Flush into this object	Whole extra objects on the plate	They print in shifting colors, so use them for functional parts or parts you will paint

OrcaSlicer’s wiki notes that these options only work with the prime tower enabled. In Bambu Lab’s example, sacrificial objects absorbed nearly all of the roughly 70 g the colored cube would otherwise flush. Less than a gram went to waste. Enter the share your slicer reports as redirected in the infill field to see the grams saved.

What to do with purge waste

• Sort the blobs by material. Mixed plastics are harder to reuse than a single type.
• Some owners regrind single-material scrap into new filament with a filament recycling extruder.
• Some filament makers and recycling services accept printing scrap. Check what they take before sending it.
• Ask your local recycling program before using curbside bins. Acceptance of 3D printing scrap varies.
• Small blobs work as craft material or packing filler.

What is the cost difference between a multi-color and a single-color print?

The difference is the price of the wasted filament plus the extra machine time. In the worked example, a 50 g PLA figurine at 20 per kg costs 1.00 in filament printed in one color and 2.04 with 150 color changes. The 52.1 g of flush more than doubles the filament bill.

Example costs at 20 per kg

These rows use the default 280 mm³ PLA flush, no tower and no redirect:

Model	Changes	Waste	Single color	Multi-color	Waste share
50 g figurine	150	52.1 g	1.00	2.04	51.0%
50 g figurine	300	104.2 g	1.00	3.08	67.6%
200 g model	150	52.1 g	4.00	5.04	20.7%
200 g model	600	208.3 g	4.00	8.17	51.0%

Multi-color cost scales with changes per gram of model. Small, detailed parts carry the highest markup. For electricity, machine wear and labor on top of filament, run the finished numbers through the print cost calculator. If you need the flush as meters of filament rather than grams, use the filament length and weight converter.

Is a manual color swap cheaper than an automatic material system?

Per print, a manual swap can use less filament when colors change only between layers, because a model with a few color bands needs a few swaps. An automatic system such as the Bambu Lab AMS or Prusa MMU changes color within a layer, which a manual swap cannot do, and flushes at every change.

What differs between the two

	Manual color swap	Automatic material system
Where color can change	Between layers only	Within a layer
How it runs	The printer pauses and waits for you, per Prusa’s color change guide	Unattended
Waste per change	What you purge and trim by hand	The slicer’s flush table plus prime tower
Typical change count	A handful per print	Up to several per layer
Purge tower	Usually none	On by default in Bambu Studio

The two methods suit different designs. A layered sign or a banded vase needs only a few swaps. A figurine with painted eyes on every layer needs color inside the layer, which only an automatic system prints.

Comparing them with this calculator

Run the calculator twice. For the manual swap, enter the number of swaps, the purge you extrude by hand as flush volume, and any trimmed tip length. For the automatic system, use the slicer’s change count, flush table and tower weight. Add your own time for each manual swap, since you must be at the printer. The cost of a failed swap belongs in the failed print cost calculator.