An injection molding budget has two distinct layers: fixed tooling and launch cost, paid before or around production approval, and variable part cost, incurred as acceptable parts are molded, inspected, finished, packed and shipped. Keeping those layers separate makes quotations easier to compare. A low mold price can hide incomplete tooling scope, while an attractive piece price can rely on an unrealistic cycle time, cavity count or annual volume.
This guide explains a transparent estimating method for product engineers and buyers. The figures are a hypothetical example, not a CKMOLD quotation. Use the injection mold cost calculator to organize early assumptions, then submit CAD and project requirements for an engineering-reviewed quotation.
The Basic Injection Molding Cost Formula
For an early project comparison, use the following structure:
Variable part cost = resin + machine conversion + direct labor and overhead + scrap allowance + secondary operations + packaging and inspection
Amortized tooling cost per part = tooling and agreed launch cost ÷ planned production quantity
Budgeted cost per part = variable part cost + amortized tooling cost per part
A commercial quotation may also include freight, duty, tax, inventory, financing, currency risk and supplier margin. These items should be identified rather than blended into an unexplained “molding cost.” The quotation should also state the Incoterm and currency so the buyer knows where cost and risk transfer.
Fixed Costs and Variable Costs
| Cost group | Typical inputs | Questions to clarify |
|---|---|---|
| Mold and hot runner | Cavities, actions, steel, components, finish, expected duty and destination standard | Is the quote for a complete transferable mold or for inserts in a supplier-owned mold base? |
| Engineering and launch | DFM, mold design, simulation, trials, samples, reports, gauges and approved corrections | How many trials and correction cycles are included, and what defines acceptance? |
| Resin | Part and shot weight, price per kilogram, color, additives, runner treatment and yield | Is pricing based on a named commercial grade and a current material quotation? |
| Machine conversion | Press hourly rate, cycle time and saleable parts per cycle | Does the selected press provide the required clamp force, shot capacity, tie-bar clearance and process control? |
| Labor and overhead | Loading, trimming, inspection, handling, maintenance and plant burden | Which steps are automated, operator-attended or performed by sampling? |
| Secondary work and logistics | Printing, painting, assembly, packaging, freight and duty | Which operations and delivery terms are included in the stated unit price? |
How to Calculate Resin Cost per Part
Use material actually consumed per saleable part, not only the net CAD mass. A runner, sprue, purge loss, startup scrap and rejected parts can all increase purchased resin consumption.
Resin cost per part = purchased resin per saleable part × resin price per kilogram
If the estimate starts from shot weight, use:
Resin cost per part = (shot weight × resin price per kilogram) ÷ saleable parts per shot
Then apply the agreed nonrecoverable loss assumption. If clean runner regrind is permitted, state the percentage and the cosmetic, mechanical or traceability limits. Optical parts, flame-rated components and tightly controlled applications may restrict regrind. Color masterbatch, glass or mineral reinforcement and moisture-sensitive grades can also change density, price, wear, drying cost and yield. A material family such as “ABS” or “PA66” is not a final pricing specification; the supplier, grade, color and additives matter.
How to Calculate Machine Cost per Part
Machine cost per part = press hourly rate × cycle time in seconds ÷ 3,600 ÷ saleable cavities
The cavity term must represent cavities producing acceptable parts. A four-cavity mold running with one cavity blocked does not have four-cavity economics. Family molds need a different analysis because the cavities may produce different parts, weights and demand ratios.
Cycle time includes mold closing, injection, pack and hold, cooling, opening, ejection and any robot or manual handling that delays the next shot. Cooling is often the largest component, but the limiting step depends on wall thickness, resin, geometry, ejection and downstream handling. A quoted cycle should be treated as an engineering assumption until it is demonstrated during trial.
Worked Injection Molding Cost Example
The following example is deliberately transparent so a buyer can replace each assumption. It is not a price offer.
- Two saleable cavities
- 30-second molding cycle
- Press rate of USD 75 per hour
- 50 g of purchased resin per saleable part, including the allocated runner and purge basis
- Resin price of USD 3.20 per kg
- 3% material loss allowance
- Labor and overhead of USD 0.10 per part
- Secondary operation of USD 0.20 per part
- Packaging and inspection of USD 0.08 per part
- Mold and agreed launch cost of USD 24,000
- Planned production quantity of 100,000 parts
| Line | Calculation | Estimated cost per part |
|---|---|---|
| Resin | 0.050 kg × USD 3.20 ÷ (1 − 0.03) | USD 0.165 |
| Machine | USD 75 × 30 ÷ 3,600 ÷ 2 | USD 0.313 |
| Labor and overhead | Stated assumption | USD 0.100 |
| Secondary operation | Stated assumption | USD 0.200 |
| Packaging and inspection | Stated assumption | USD 0.080 |
| Variable subtotal | Sum of the variable lines | USD 0.858 |
| Tooling amortization | USD 24,000 ÷ 100,000 | USD 0.240 |
| Budgeted total before excluded items | Variable subtotal + tooling amortization | USD 1.098 |
Rounding this result to about USD 1.10 per part is more honest than presenting unnecessary decimal places. Freight, duty, tax, inventory, financing and the quotation’s margin treatment remain outside this simplified example unless expressly included.
Sensitivity: Which Assumptions Change the Result Most?
A cost model becomes useful when it shows which inputs deserve engineering attention. The table below changes one input at a time and holds the other example assumptions constant. A real redesign can change several inputs together.
| Input change | Directional effect in this example | Engineering caution |
|---|---|---|
| One cavity instead of two | Machine cost rises by about USD 0.313 per part | The tool may be simpler, but output is lower. |
| Cycle falls from 30 s to 24 s | Machine cost falls by about USD 0.063 per part | Confirm dimensions, appearance, cooling and handling remain acceptable. |
| Resin rises from USD 3.20 to USD 4.00/kg | Resin cost rises by about USD 0.041 per part | Density, runner and loss assumptions still matter. |
| Material loss rises from 3% to 8% | Resin cost rises by about USD 0.009 per part | Rejected parts also consume machine time and labor. |
| Planned volume falls to 25,000 | Tooling amortization becomes USD 0.96 per part | The tool may be re-scoped for lower lifetime demand. |
| Planned volume rises to 250,000 | Tooling amortization becomes USD 0.096 per part | Higher cavities or more durable construction may change mold and validation cost. |
Cycle, cavities, press size and mold cost are not independent. More cavities can require a larger mold, larger press, more complex hot runner, stronger cooling and higher initial investment. Compare complete scenarios rather than multiplying a one-cavity result without changing the tooling assumptions.
What a Tooling Quote Should State
A defensible comparison should identify whether the quoted scope includes:
- DFM review, mold-design iterations and the approved file revision;
- a complete mold base or cavity and core inserts only;
- steel and component brands, hardness, heat treatment and certificates;
- hot runner, connectors and destination-machine interfaces;
- texture, polishing, engraving and coatings;
- trial count, sample quantities and measurement reports;
- gauges, fixtures, capability studies or customer report formats;
- corrections needed to meet agreed acceptance criteria;
- spare and wear parts, preservation, packing and export documents; and
- freight, duty, tax, installation or destination support.
If the mold will stay with the molding supplier, clarify ownership, maintenance, storage, replacement and transfer terms. If it will ship to another plant, review the export injection mold requirements for the receiving press and plant standard.
Why Part Length, Width and Height Are Not Enough
An envelope size does not reveal undercuts, shutoffs, thin steel, parting-line constraints, gate restrictions, cooling access, tolerances, resin behavior, surface finish, expected tool duty or destination press. Two parts with the same bounding box can require very different tooling and cycle economics.
A useful RFQ identifies the 3D CAD revision, controlled 2D drawing, intended resin grade or performance requirements, finish, color, critical dimensions, first order, estimated annual volume, total program volume, required quality records, shipping destination and launch target. If CAD is available, send it as an email attachment to jerry@ckmold.com after submitting the form.
Budget Estimate Versus Formal Quotation
The calculator and formulas provide a planning range. They do not inspect the geometry or confirm a mold design, process window, cycle, quality plan, logistics cost or commercial terms. A formal quotation should list assumptions, inclusions, exclusions and approval stages. Missing inputs should appear as open assumptions rather than being hidden behind a precise-looking price.
For a project-specific mold and part-cost breakdown, submit an injection molding RFQ. For production supply options, review production injection molding.
Injection Molding Cost Questions
Should tooling be included in the piece price?
Tooling can be paid separately or amortized, but the quotation should state the quantity basis, tool ownership and what happens if actual volume differs from the plan.
Is a shorter cycle automatically better?
No. A shorter cycle is valuable only if parts continue to meet dimensional, cosmetic, mechanical and handling requirements across the approved process window.
Why can a higher-cavity mold be uneconomic at low volume?
The larger upfront tool, hot-runner and validation cost may not be recovered through machine-time savings when total demand is limited. Demand timing also matters: a short peak may justify capacity that the same annual volume spread evenly would not require.
What information is needed for a useful estimate?
Provide part geometry, material or performance requirements, quantities, finish, critical tolerances, quality documentation, target timing and delivery location. The estimate should identify any item that is not yet known.