Silicone Mold & Casting Resin Specific Gravity Chart & Volume Formulas
To convert mold volume (cm³ or mL) into exact casting weight in grams, multiply the volume by the material's Specific Gravity (SG): W_grams = V_cm³ × SG × (1 + Waste Buffer). Platinum RTV-2 silicone averages SG = 1.07 to 1.15, deep-pour epoxy is 1.11, and Jesmonite AC100 is 1.75.
Master Reference Lookup Table
Filter by name or click column headers to sort specifications.
| Action | ||||||
|---|---|---|---|---|---|---|
| Clear Water-Resin Polyurethane (Clear Flex 50) | Resin | 1.08 | 1:2 (weight) | 20 mins | 48 hrs | Mold Calculator → |
| Deep Pour River Epoxy (2:1 Ratio) | Epoxy | 1.11 | 2:1 (weight) | 90 mins | 72 hrs | Mold Calculator → |
| Dragon Skin FX-Pro (Prosthetic Silicone) | Silicone | 1.07 | 1:1 (weight) | 12 mins | 4 hrs | Mold Calculator → |
| Fast-Cast Polyurethane Resin (Smooth-Cast 300) | Resin | 1.05 | 1:1 (weight) | 3 mins | 2 hrs | Mold Calculator → |
| Hydrocal / Pottery Plaster (USG Plaster) | Plaster | 1.65 | 1.42:1 (weight) | 8 mins | 24 hrs | Mold Calculator → |
| Jesmonite AC100 (Eco-Resin) | Jesmonite | 1.75 | 2.5:1 (weight) | 12 mins | 24 hrs | Mold Calculator → |
| Jesmonite AC730 (Stone Casting) | Jesmonite | 1.85 | 5:1 (weight) | 15 mins | 24 hrs | Mold Calculator → |
| RTV-2 Platinum Silicone (Smooth-On Mold Star 15/30) | Silicone | 1.07 | 1:1 (weight) | 30 mins | 16 hrs | Mold Calculator → |
| RTV-2 Tin Cure Silicone (Condensation Cure) | Silicone | 1.12 | 10:1 (weight) | 45 mins | 24 hrs | Mold Calculator → |
| Table Top & Art Epoxy (1:1 Ratio) | Epoxy | 1.08 | 1:1 (weight) | 25 mins | 24 hrs | Mold Calculator → |
Core Mathematical & Engineering Breakdown
Datasheet equations, derivations, and step-by-step worked shop math.
The #1 Cure Failure Trap: Mixing by Weight vs. Mixing by Volume
Many beginners assume a 1:1 by-volume epoxy or silicone can simply be weighed 1:1 on a gram scale. This causes severe cure failure. For instance, in many polyurethane casting resins, Part A has a specific gravity of 1.15 while Part B is 1.02. Measuring 100g of Part A and 100g of Part B introduces a 12.7% stoichiometric imbalance, resulting in a sticky, rubbery, permanently uncured casting. Always check the manufacturer datasheet to verify whether the ratio is specified by weight (pbw) or volume (pbv).
The Water Displacement Trick for Irregular 3D-Printed Masters
Calculating the volume of organic 3D prints or sculpted miniatures using math formulas is impossible. The shop-proven solution is water displacement: Place a container filled to the brim with water on a digital scale and tare to 0.0g. Submerge the master model completely under water with a thin wire and catch the overflow, or submerge it without touching the walls and record the weight increase. Because 1.0g of distilled water equals exactly 1.0 cm³ (1.0 mL) at room temperature, the gram reading equals your master's volume.
Geometric Volume Formulas for Boxes, Cylinders, and Hemispheres
For rectangular containment mold boxes: Volume = Length × Width × Height. For cylindrical molds: Volume = π × (Diameter / 2)² × Height. For hemispherical cavities: Volume = (2 / 3) × π × Radius³. To find required silicone pour volume around a positive master: V_pour = V_containment_box - V_master.
Interactive Micro-Tool: Real-Time Calculation
Adjust sliders and inputs below to calculate custom dimensions instantly.
Casting Material & Volume Mode
Pre-loads specific gravity and 1:1 ratio by weight.
Geometry determines the container-volume formula. Use water displacement when the cavity is irregular.
Volume displaced by your master object inside the box.
Compensates for resin clinging to mixing paddles and cup walls (8% recommended).
Includes 8% waste buffer at SG 1.07
Ratio part: 1
Ratio part: 1
Net volume before buffer
Order RTV-2 Platinum Silicone (Smooth-On Mold Star 15/30) Kit
High-tear strength RTV-2 Platinum Silicone (Smooth-On Mold Star 15/30) with verified 1:1 ratio. Ideal for bubble-free casting.
Failure Modes & Workshop Troubleshooting Matrix
Common fabrication failures, caliper inspection methods, and prevention rules.
| Failure Mode | Root Cause | Caliper / Scale Check | Shop Prevention |
|---|---|---|---|
| Resin cast remains tacky and soft after full cure duration | Stoichiometric imbalance caused by mixing a 1:1 volume resin by weight | Component A density (1.18 g/cm³) differed significantly from Component B (1.04 g/cm³) | Consult MetriFab casting database for ratioType: weight vs volume before dispensing |
| Silicone mold runs short 1/4" before covering top of master | Zero waste buffer added to calculation; residue remained stuck to mixing bucket walls | 60g of high-viscosity silicone left coating the sides and paddle of the 1000mL container | Always configure a 8% to 12% safety waste buffer on viscous materials |
| Air bubbles trapped against detailed vertical mold surfaces | High-viscosity silicone poured too fast without degassing or high-pour thin stream | Viscosity exceeding 25,000 cPs without vacuum degassing chamber | Pour silicone in a hair-thin stream from 24" height to stretch and burst air bubbles |
Frequently Asked Engineering Questions
High-intent technical fabrication inquiries verified against lab standards.
Q1What is specific gravity and how does it convert volume to weight?
Q2Why can't you mix all 1:1 volume resins on a digital gram scale?
Q3How do you measure the exact volume of an irregular 3D printed model?
Q4What waste buffer percentage should I add when mixing silicone molds?
Related Programmatic Calculators in this Silo
Launch individual entity calculators pre-configured with exact manufacturer specifications: