Injection Molding Cost per Unit: Material, Machine and Tooling Explained

The Four Building Blocks of the Unit Price

Every serious quote for an injection-molded part reduces to the same structure:

The first two blocks are variable: they occur with every shot and scale linearly with volume. Tooling amortization is a fixed-cost share distributed over the order quantity, which is why the same geometry costs far more per part at 10,000 units than at 100,000. Post-processing is everything that happens after the part leaves the tool: degating, decorating, assembling, packaging.

Whoever examines these four blocks separately immediately understands why two quotes for the same part can diverge: one supplier calculates with a 60-second cycle and a single cavity, the other with 40 seconds and two cavities. Same quality, different process, nearly double the unit price. What a full project looks like cost-wise, tool included, is covered in detail in injection molding costs for a housing.

Building Block 1: Material Costs

Material cost per part equals shot weight times the resin price per kilogram. Note that the shot contains more than the part: with a cold-runner tool, sprue and runner end up as scrap or regrind. Calculate with the full shot weight, not the part weight.

For a housing with a 55 g part weight and about 10 g of runner, that is 65 g per shot. At typical granulate prices, the material costs per part look like this:

Two things stand out. First, for thin-walled standard parts the material share is a surprisingly small 10 to 20 percent of the unit price: haggling over cents in the granulate price rarely pays off. Second, the picture changes for massive parts or high-performance resins: a 300 g part in POM carries more than a euro of material alone, and suddenly the resin is the largest cost block. The systematic material selection with criteria and price ranges is covered in material selection for injection molding.

Building Block 2: Machine Costs

Machine cost per part follows simple logic: every machine hour costs money, and every hour produces a known number of parts. The machine rate for mid-size presses typically sits between €60 and €100 per hour including operator, energy and drying. Divided by the cycle time times the cavity count, you get the machine share per part.

A worked number: a 45-second cycle at an €80 hourly rate with two cavities yields 45 ÷ 3,600 × 80 ÷ 2 = roughly €0.50 per part. Three levers sit inside that formula:

• Cycle time – the biggest lever. Cooling dominates the cycle and grows with the square of wall thickness. Thinner walls save time first, material second.
• Cavity count – two cavities halve the machine cost per part because two parts emerge per cycle. Going from one to two cavities costs tooling, but pays back at moderate volumes almost always.
• Machine size – the tool's projected area and shut height determine the press class. A slim tool on a smaller machine runs at a lower hourly rate.

With 30 instead of 45 seconds of cycle time, the machine share in the example drops from €0.50 to about €0.33 per part. Same geometry, over a third less variable cost. The reverse path is the single cavity: 45 seconds on one cavity costs €1.00 per part, twice the two-cavity variant. When multi-cavity tools pay off, and where their limits lie, is treated in a dedicated article on multi-cavity molding.

Building Block 3: Tooling Amortization

The third block is not a process cost but an accounting split: the tool is a one-time investment distributed across the ordered quantity. How strongly it moves the unit price is shown by the same €12,000 two-cavity tool at different volumes:

This table explains the defining phenomenon of injection molding: the unit price falls with volume, but not linearly. It approaches a floor made of material and machine costs. From 10,000 to 100,000 parts the price drops by more than half; from 50,000 to 100,000 only by 12 cents. Tooling amortization is also why low-volume runs need a different economic view: at 500 parts, the same tool would carry €24 per part. Which tool class fits which volume is covered in the small-batch injection molding cost guide.

Also note what this calculation leaves out: tool maintenance, spare parts and tool life. An aluminum tool from around €1,500 is finished after a few thousand shots; a hardened steel tool survives several hundred thousand. At high total volumes the more expensive steel tool ends up cheaper per part despite its higher purchase price. The typical mistakes that cost money in tool making are listed in the article on expensive tooling mistakes.

Building Block 4: Post-Processing and Often-Forgotten Items

Out of the tool, the part exists but is not yet shippable. Post-processing includes degating, surface treatment such as painting, printing or texturing, inserting metal components and packaging. For a simple housing that is 8 cents per part in the example; with cosmetic surfaces or assembly steps it quickly becomes 30 to 50 cents.

On top come items often hidden or unitemized in quotes: scrap and startup material while dialing in the tool, quality inspection and metrology, packaging and freight. Ask explicitly which of these items the unit price includes, and whether degating was calculated as manual or machine work. This is exactly where the surprises sit between two quotes that differ by 20 cents on paper.

Worked Example: Unit Cost of a Housing

Now all four blocks together. Assumptions: ABS housing, 55 g part weight, 65 g shot weight including runner, 45-second cycle, two-cavity tool at €12,000, machine rate €80/h, order quantity 50,000 parts, 8 cents post-processing.

Total: roughly €0.98 per part, all prices net plus VAT. The same calculation with one cavity would give €1.48; a process optimized to 30 seconds lands around €0.82. That is the entire spread that process decisions alone produce, before anyone negotiates the granulate price.

Two caveats for context. First, this is a planning calculation from experience values, not a quote; the actual price depends on tool design, region, order size and delivery scope. Second, the comparison with the alternative is worth running: CNC-machined versions of the same geometry in small batches run €4 to €8 per part depending on effort. Where exactly the injection molding break-even sits is shown in the next section.

Break-even: When Injection Molding Beats CNC and 3D Printing

The break-even quantity follows from dividing the tool investment by the saving per part. In the example the molded part costs about €0.98, the machined part €8. The variable saving is roughly €7, the tool costs €12,000:

From roughly 1,700 parts the tool has paid for itself; every part beyond saves more than €7. With a cheaper CNC alternative at €4, the threshold moves to about 3,700 parts. The general rule of thumb stands: injection molding pays off from a few thousand parts; below that, CNC and 3D printing are more economical. Which prototyping processes make sense until then is shown in the prototyping cost comparison. For planning a real production launch with quality assurance and documentation, the guide to production injection molding is the next step.

The Five Levers for a Lower Unit Price

1. Reduce wall thickness. Shorter cooling times cut the cycle directly. From 2.5 mm walls, 35 instead of 45 seconds are quickly realistic.
2. Increase the cavity count. Two cavities halve the machine share. Compare the tooling expansion against the saving per part.
3. Design without side actions. Every side action drives tooling and cycle. If undercuts can be avoided constructively, you win twice.
4. Choose material by total cost. The price per kilogram is nearly irrelevant; processability decides. A resin with shorter cooling time can be cheaper per part than the supposedly bargain granulate.
5. Bundle your volume. Calling off your annual demand in one batch spreads tooling amortization across more parts. Inventory costs less than a high unit price.

All ten levers with price examples are covered in detail in cutting injection molding costs: 10 concrete levers. And because every cheap part starts with a manufacturable design: the DFM review before tool making decides whether these levers are available at all. The full service, from design through tool accompaniment to acceptance, is described on the injection molding service page.

Frequently Asked Questions About Unit Costs