RTV Volume Calculator: Box, Master, Waste | RUUIPON

A "silicone volume calculator" is only useful if you feed it the right three volumes: the inside of the mold box, the displaced volume of the master (and cores), and the waste you will never recover — cup heel, vacuum foam, keys, sprue, and the extra you mix so you do not short the last corner. Subtract master from box, convert cm³ to grams with the grade density, then add a waste factor. Skipping waste is how a 1:1 platinum mix dies mid-pour and leaves a foam face you cannot sand back on a food logo. We quote rubber by that stack, not by outer tray size.

RUUIPON pours platinum RTV tools in Bao'an since 2018: master, box, A/B mixed 1:1 or 10:1 by weight, vacuum degas, keys, jacket. Prototype is 3–7 business days after CAD lock. Production is MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. Steel/LSR *parts* are a different mass conversation at wydsilicone.com. Quote fields: custom mold quote.

Does not apply when you are buying a compression HCR *part* (preform weight is a mill ticket, not a box calc), when the "mold" is a purchased stock tray with unknown wall, or when you want us to guess grams from a phone photo of a figurine with no box dims. Also does not apply to a mother-mold jacket poured in plaster or resin — that is a second material, not RTV volume.

The three volumes you actually put on a scale

Box interior. Length × width × pour height to the planned shut, in centimetres. Do not use the plywood outside. If the box has a draft or a clay dam, use the *wetted* envelope after the dam. A 300 × 200 × 40 mm interior is 2,400 cm³ before anything sits in it.

Master displacement. The pattern occupies volume the rubber will not. CAD is the honest number. A water-displacement check on a sealed master is the shop backup when the STL is hollow or scaled in inches. Cores, pour plugs, and registration bosses that stay in the box during the pour subtract too. A hollow print that floods internally *adds* rubber unless you seal the print first.

Waste. Typical shop practice is a 10–20% extra on small pours and 5–10% on large block pours, plus a cup heel so the vacuum chamber does not run dry. Foam that climbs the bucket during degas is rubber you already mixed; it is not free. Keys, a brushed detail coat, and a second mix if the first pot-life dies all add grams. We would not mix "exactly the calculator number" on a food logo skin.

Density converts volume to grams. Platinum RTV is often around 1.1 g/cm³; use the TDS for the named grade, not a blog average, when the PO is tight. Mix 1:1 or 10:1 *by weight*, never by the volume marks on a cup.

What web calculators forget

Keys and a keyed jacket interface are extra rubber sitting outside the cavity. An open-back glove uses less rubber than a block pour of the same part — that is a structure decision, not a calculator trick. A mother mold jacket is a different material; do not add plaster kilograms into the RTV line.

Vacuum degas makes the mix look taller before the foam collapses. If you fill the cup to the brim "to match the calc," you will overflow the chamber and starve the box. Leave headspace.

Loaded-tray sag of about 0.5–1.5 mm is a jacket problem, not a "pour more silicone" problem. Extra wall thickness is usually the expensive way to fake stiffness. See mother-mold jacket.

Typical shop values

Caption: Typical shop values. Not a named PO.

Copy-ready volume sheet (method, not a result)

Fill the blanks before anyone opens a drum.

flowchart TD
  A[Need RTV grams] --> B[Measure box interior after dam]
  B --> C[Subtract master + cores]
  C --> D[cm3 x TDS density]
  D --> E[Add waste: cup heel + foam + keys]
  E --> F{Open-back glove or block?}
  F -->|Glove| G[Less rubber; still jacket if wet/tall]
  F -->|Block| H[More rubber; check pot life vs volume]
  G --> I[Weigh A/B 1:1 or 10:1]
  H --> I

Common mix-up: millilitres on the cup equal grams on the PO

Buyers send "800 ml of silicone" from a kitchen jug. A/B is weighed. A 10:1 grade grabbed off volume marks is how you get a sticky face and a hard back. Another mix-up: quoting one rubber weight for twenty production skins from a prototype that used a smaller box. MOQ 20 is twenty of the *locked* design, each needing its own grams plus a shared master. Recast grams can be lower if the jacket already exists and you only pour the skin.

Worked example (anonymized)

A resin figurine, block mold. Box interior 180 × 120 × 70 mm → 1,512 cm³. Master displacement from STEP 420 cm³. Net 1,092 cm³. Density 1.10 → about 1,201 g net. Waste 15% because it is a first vacuum pour with keys → about 1,380 g to weigh, split 1:1. Jacket was plaster, quoted as a separate line. CAD was USD $50 because we only had photos; lock, then 3–7 business days for the prototype skin. Production was MOQ 20 of that keyed block, not "20 kg of leftover rubber." Food was never on this PO — jewelry-adjacent resin is not a 177.2600 article.

We would not recommend

We would not recommend mixing to the exact net grams with no heel.

We would not recommend thickening the RTV wall to replace a jacket on a wet dump.

We would not recommend volume-marking a 10:1 platinum on a food cavity.

We would not recommend guessing box height from a lifestyle photo of the finished soap.

What to ask when you're buying

• Will you quote rubber grams from CAD, or from a box you have not designed yet?
• Is the jacket in the same line as the RTV, or separate?
• What waste factor do you mix on a first pour versus a recast?
• Is this an open-back glove or a block — because the grams are not the same?
• After CAD lock, is the prototype still 3–7 business days, then MOQ 20?

RFQ copy-pack (volume inputs)

Email [email protected]:

Part envelope L x W x H and cavity count Box plan or "you design the box" Master: STEP / sealed print / physical Structure: open-back / block / split / plug Jacket: yes/no and material Pour: food / resin / wax / plaster / concrete (concrete and jewelry are not food) Mix: platinum 1:1 or 10:1 CAD: lock in hand / USD $50 if you model Prototype 3–7 business days after CAD lock, then MOQ 20 / design

Send the envelope and the structure. We will size rubber from box − master + waste, not from a viral calculator. Phone +86 135 3006 2969. Checklist: RFQ checklist.

FAQ

Can I use an online silicone calculator and just send you the grams? Send box interior, master volume, and structure. Calculators that skip waste, keys, and open-back vs block will short a pour. We re-run the stack.

Is 1 ml of RTV equal to 1 gram? Usually not. Use the named-grade density, often around 1.1 g/cm³, and weigh A/B. Volume marks on a cup are how 10:1 mixes go wrong.

Does platinum shrink change how much I mix? Typical platinum shrink is about 0.1–0.3% linear. You still mix the grams to fill the box. Compensation lives on the master, not in a smaller cup.

If I order MOQ 20, is that 20 times the prototype grams? Twenty skins of the locked design, each needing its pour, unless we are recasting into an existing jacket with a defined skin volume. Ask us to split prototype grams vs production grams.

Do I pay USD $50 to get a volume number? The $50 is for simple 3D when that CAD scope applies. Volume is a quote input we can run from a STEP. Photos-only still needs a model before the grams are honest.