3D printing in batches: how to work out the cost per part

What you pay per plate and what you pay per part

Every print has costs that do not change with the number of parts on the plate:

• Your prep time: slicing, cleaning the plate, checking the filament, starting the print and watching the first layer.
• The start of the print: heating the bed and nozzle, leveling, calibrating, purging and laying the prime line. That is a few minutes of machine time and a few grams of filament, every print.
• First-layer risk: a greasy or badly leveled plate loses the print at the start, whether it holds one part or ten.

And there are costs that grow with each part: its filament, the machine time to print it and the finishing, such as removing it from the plate, cleaning off supports and packing it.

The cost per part combines both:

cost per part = plate costs ÷ number of parts + cost of each part

The first term shrinks with every part you add; the second stays the same. That is why the first few extra parts bring almost all the savings, and the last ones almost none.

Example: 1 part alone vs 10 on the same plate

Suppose a PLA cable organizer. Sliced on its own, the slicer shows 48 minutes and 14 g, including the 8 minutes and 2 g for the start of the print. With 10 copies on the same plate, it shows 6 h 48 min and 122 g.

Math example, not a measurement: PLA at $20/kg; a machine rate of $0.17/h with the calculator's starting values (see the guide to 3D printer cost per hour); your time at $30/h.

The cost per part drops 76%. Now look only at material, electricity and machine: per part, they go from $0.42 to $0.36, a 14% drop. Almost all of the batch savings is your prep, done once and split ten ways. If you do not count your own time, the batch barely changes the cost, but it changes the time you spend a lot: 15 minutes of prep for a single part against 1.5 minutes per part in the batch.

In practice, a full plate does not take exactly ten times as long as one part. On its own, a small part may have its layers slowed down by the slicer to respect the minimum layer time for cooling, which stops happening with ten parts; on the other hand, travel moves from one part to the next add time. Slice the whole plate and use the time and weight the slicer shows.

In the calculator, import the sliced file for the whole plate and enter how many parts it holds in Parts in this print: cost and price come out per part. In the Bundles section, the How many fit on the plate field caps the batch suggestion at what your plate holds.

How much the cost drops with each extra part

Same premises as the example: 40 min and 12 g per part, 8 min and 2 g of print start per plate, 15 min of prep per plate and 2 min of finishing per part. The drop is on the cost with your time.

Going from 1 to 4 parts cuts the cost per part by 64%. Going from 10 to 20 saves only $0.38 more per part, and the plate goes from 6 h 48 min to 13 h 28 min, a full night of printing.

The other side: one failure can take the whole plate

A batch shares the costs, but it also pools the risk:

• One failure hits every part. A part that comes loose can be dragged by the nozzle and knock over its neighbors. A clog in the fifth hour ruins all ten.
• The print gets longer. More hours exposed to a power outage, a filament tangle or the end of a spool.
• There is more first layer to go wrong. More of the plate covered means more chance of a dirty or uneven spot.

Run the math with example numbers, not statistics: suppose the chance of losing the print is 3% with one part and 8% with the plate of ten. The expected loss per part is that chance times what you lose in material, electricity and machine: 3% × $0.42 = $0.01 alone, and 8% × $0.36 = $0.03 in the batch. Even with almost three times the risk, the expected loss rises by $0.02 per part, against $6.81 saved.

The cost that weighs most is the deadline. Losing a 6 h 48 min plate near the end delays the whole order, because everything has to be printed again. To lower that risk:

• Print one part first, with the same file, the same filament and the same build surface.
• Leave space between parts and add a brim to tall, thin ones.
• If the parts are short, print them one at a time: Print sequence: By object in Bambu Studio and OrcaSlicer, Complete individual objects in PrusaSlicer and Print Sequence: One at a Time in Cura. A failure then loses only the part being printed. The slicer warns you when a part is too tall for this.
• Watch the first layer of the whole plate before you walk away.

The guide to failure rate pricing shows how to turn your failure rate into a reserve inside the cost.

A practical rule: when to fill the plate

Fill the plate when all four are true:

1. The part has already come out right at least once, with the same file, filament and build surface.
2. There is an order or steady demand for the parts. A lower cost per part is no reason to print stock you have no clear way to sell: it is money sitting on a shelf.
3. The print finishes at a time when you can check it, or the printer has failure detection.
4. The parts are short and have a good footprint. Tall, thin parts call for fewer copies per plate, a brim or printing by object.

Split it into two plates when a full plate would run overnight with nobody around and a failure would delay an order with a deadline, or when the extra part barely changes the cost, as from 10 to 20 in the example. Keychains are the classic batch print, and the guide to keychain pricing runs the numbers for them.

Frequently asked questions

Do different parts on the same plate count as a batch?

Yes: prep and the start of the print are still paid once. What changes is how you split the cost. The calculator divides the plate cost equally among the parts you enter, which works for copies of the same part. For very different parts, slice each one alone to get its weight and time, and split the plate cost in that proportion.

Does filling the plate pay off even more with resin?

On an MSLA resin printer, the screen exposes the whole layer at once, so print time depends mainly on the height of the tallest part, not on how many parts are on the plate. Filling the plate spreads that time, the electricity and the machine wear across more parts; resin is still used per part. The guide to resin printing cost runs the full numbers.

Can I give a discount for bulk orders?

You can, and the math shows where it comes from: the prep you did not have to repeat, not your margin. In the example, the cost per part goes from $8.92 to $2.11 at ten units. In the Bundles section, the calculator shows the price of each bundle with the same margin you use for single parts. The guide to how much to charge explains the margin.

How many parts fit on the plate?

Use the slicer's auto-arrange and leave space between parts so the nozzle does not drag one into another and the fan's airflow can get around them. With parts packed too close, one that comes loose can knock over its neighbors. Once you find your number, enter it in How many fit on the plate in the calculator.

What if only one part on the plate fails?

You lose that part's material and machine time, and the others survive if the print stays clean. Some printers let you cancel just that object mid-print: the feature is called Skip objects on Bambu Lab printers and Cancel object on Prusa printers. To cover that kind of loss in your price, the calculator adds a failure reserve as a percentage of material, electricity and machine.