Gummy Mold Cavity Volume: How to Spec Fill Weight Before Tooling

Your nutrition label says 3 g per bear but the cavity pours 3.8 g - that is a cavity volume spec error, not a recipe problem. RUUIPON builds custom gummy molds at MOQ 50 with prototypes in 3-7 days. This guide shows how to calculate cavity volume, convert to fill weight before tooling, and lock tolerances your depositor can hold.

Quick answer: Cavity volume (cm³) × slurry density (~1.05-1.25 g/cm³ for hot gummy) = target fill weight. CAD volume minus ~0.1% silicone mold shrink gives molded cavity; add 2-5% process band for evaporation and tail drip. Spec target weight ±0.2 g on a 3 g piece - not "about 3 g."

Why Fill Weight Starts in CAD, Not the Kitchen

Tooling locks cavity geometry - you cannot shrink a 4 g cavity to 3 g without new molds at MOQ 50.

Step	Action
1	Model cavity solid in CAD; measure volume in cm³
2	Apply silicone shrink ~0.1% to expected molded volume
3	Multiply by hot slurry density (measure yours)
4	Prototype weigh 10 pieces; adjust CAD or depositor
5	Lock weight on PO before MOQ 50 production

Cavity Volume Math & CAD Workflow

Simple shapes: volume = area × depth. Complex bears and worms: use CAD mass properties - do not estimate from bounding box.

• Example - 2.8 cm³ cavity × 1.12 g/cm³ hot gelatin = 3.14 g target.
• Silicone shrink - mold cavity ~0.1% larger than master; negligible on 3 g but matters on 25 g blocks. Shrinkage guide.
• Draft angles - 3-5° sidewall draft changes volume slightly vs vertical CAD - include in sim. Draft & undercuts.
• Logo emboss - 0.3 mm deboss on face adds ~0.05 cm³ on 20×15 mm logo - not zero on label claims.

Full gummy design: gummy mold design guide. Gelatin vs pectin shrink differs: gelatin vs pectin.

Fill Weight, Slurry Density & Recipe Band

Formula base	Typical hot density (g/cm³)	Set shrink notes
Gelatin 150-200 bloom	1.08-1.18	~3-6% moisture loss 24 hr
Pectin HM	1.10-1.22	Slightly higher solids
Sugar-free polyol	1.05-1.15	Check hygroscopic swell
With actives (CBD etc.)	Measure batch	Do not use generic 1.1

Weigh slurry at deposit temperature (often 75-85 °C for gelatin). Density drops ~2-4% vs room-temperature cured piece weight if you forget temperature correction.

Depositor Calibration vs Cavity Volume

Manual pour: volume set by cavity overflow. Depositor: stroke volume must match cavity + 3-8% overfill for meniscus.

1. Nozzle OD - match cavity gate or open-top diameter.
2. Stroke calibration - grams per shot on scale before line speed.
3. Tray level - uneven bench = uneven fill across 24 cavities.
4. Starch bed vs bare silicone - starch absorbs edge; bare tray needs flash trim at lip.

Cavity spacing 8-20 mm; walls 2.5-5 mm; Shore A 25-35 for clean pop. Layout: multi-cavity layout. Pour geometry: spouts & vents.

Tolerance Bands, Label Claims & QC

Piece target	Reasonable production band	Label strategy
2 g micro bear	±0.15 g	Label 1.8 g serving with overfill buffer
3 g standard	±0.2 g	Target 3.0 g, spec 2.8-3.2 g internal
10 g worm	±0.4 g	Weigh-sort outliers
25 g block	±0.8 g	Cavity volume critical - no "eyeball" CAD

Food compliance: FDA vs LFGB. Sample approval must include weight sign-off. Sample checklist.

Production Spec at MOQ 50

PO line	Example
Target fill	3.0 g ±0.2 g at 80 °C gelatin 180 bloom
CAD volume	2.72 cm³ effective (signed STP rev B)
Tray	24-cavity, spacing 12 mm, walls 3 mm, Shore A 30
Process	Platinum food silicone, vacuum degassed
QC	Weigh 10/50 cavities on first production tray

Prototype 3-7 days; production ~2-4 weeks. [email protected] | Contact RUUIPON | WhatsApp +86 135 3006 2969.

Common Cavity Volume Mistakes

1. Bounding-box volume - overstates bear ears; actual fill heavy.
2. Ignoring set moisture loss - label weight is dry piece; cavity sized for hot pour.
3. Same cavity for gelatin and pectin - different densities need different volumes or depositor maps.
4. 24-cavity first tool - approve weight on 6-cavity prototype first. Prototype workflow.
5. No scale on sample approval - discover 3.8 g at MOQ 50 delivery.

Revision if weight wrong: revision process. Quote compare: compare quotes.

Frequently Asked Questions

How do I calculate gummy mold cavity volume?
Use CAD mass properties on the cavity solid in cm³; multiply by measured hot slurry density in g/cm³.

Does silicone shrink affect gummy weight?
~0.1% on mold - small on 3 g; still document on precision SKUs.

What fill weight tolerance is normal?
±0.2 g on 3 g pieces with calibrated depositor; wider on manual pour.

Can cavity depth change without new mold?
No - depth change is new tooling or revision.

What is MOQ?
MOQ 50 trays per approved volume spec.

Open-top vs gated cavities for weight?
Open-top easier for depositor; gated helps manual pour control - match your line.

Prototype weigh protocol?
10 pieces min, center + corner cavities, same recipe as production.