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How to Choose the Right Cavity Number for Your Injection Mold
Selecting the correct cavity number is one of the most critical decisions before mold making. Picking too many cavities raises your upfront tooling cost and locks up capital. Too few cavities limits output, creates bottlenecks and causes stockouts when demand rises. The cavity count directly controls your cycle time, daily capacity, per-unit cost and overall project profit.
For product and procurement teams, cavity selection is not just an engineering choice. It is a financial decision that impacts your whole product lifecycle.
What Is Mold Cavity Number?
A cavity is the hollow space inside an injection mold where molten plastic forms your finished part.
Single-cavity mold: produces 1 part per shot
Multi-cavity mold: makes 2,4,8,16 or more identical parts in one molding cycle
Family mold: creates different parts in one shot for product sets
More cavities mean higher production speed, but higher mold price, more complex machining and stricter machine requirements.
Cavity Number Recommendation by Production Volume
We split projects into three standard tiers for easy reference.
Production Tier Volume Range Recommended Cavity Suitable Steel Notes
Production Tier | Volume Range | Recommended Cavity | Suitable Steel | Notes |
|---|---|---|---|---|
Low volume / Prototype & bridge tooling | 10k – 50k pcs | Single cavity | Aluminum / P20 | New product testing, small batch, easy modification |
Medium stable volume | 50k – 250k pcs | 2–4 cavities | P20 / 718H | Best balance of mold cost & output for growing brands |
High volume mass production | 250k+ pcs | 8–32+ cavities | H13 / S136 | Hot runner recommended, for long-run mass manufacturing |
Low volume / Prototype & bridge tooling 10k – 50k pcs Single cavity Aluminum / P20 New product testing, small batch, easy modification
Medium stable volume 50k – 250k pcs 2–4 cavities P20 / 718H Best balance of mold cost & output for growing brands
High volume mass production 250k+ pcs 8–32+ cavities H13 / S136 Hot runner recommended, for long-run mass manufacturing
Note: This volume table is general guidance. Final cavity count also depends on part size, wall thickness, cycle time and available injection machine tonnage.
How to Calculate Break-Even Volume for Multi-Cavity Molds
The break-even volume tells you how many pieces you need to produce to offset the extra mold cost of a multi-cavity tool.
Break-even Quantity = Extra mold investment ÷ Per-piece cost saving
Example:
A 4-cavity mold costs $8,000 more than a single-cavity mold. It saves $0.10 for each finished part.
Break-even = 8000 ÷ 0.10 = 80,000 pieces.
You need to produce over 80,000 units to start saving money with the 4-cavity mold.
Common Mistakes When Selecting Mold Cavities
Specifying high cavity counts before CAD design is finalized, leading to costly rework
Only comparing mold price while ignoring long-term amortized tooling cost
Choosing multi-cavity molds for products with uncertain sales forecasts
Overlooking cavity balance risk: higher cavity numbers bring higher risk of inconsistent part quality
FAQ
Q1: More cavities always mean lower part price?
Not always. If your total sales are below break-even volume, high-cavity molds will increase your total cost.
Q2: Does part size affect cavity selection?
Yes. Large, thick parts need bigger machine tonnage. You cannot fit many cavities into one mold due to mold dimension limits.
Q3: What is family mold and when should I use it?
Family mold makes multiple different components in one shot. It works well for product kits, but part sizes and wall thickness need careful balancing.
Get Free Cavity Evaluation
Send your 3D drawing and sales forecast to us. Our engineering team will calculate break-even volume and recommend the optimal cavity number for your injection molding project.
