Resin Casting Volume Calculator

How to use

Know how much resin to mix before you pour.

Choose a mold shape and enter its internal dimensions, or choose Custom Volume for a known capacity. Enter the number of identical molds. Open Objects inside mold to subtract a measured displacement per mold, then choose an extra resin allowance and the manufacturer’s Part A : Part B ratio and basis.

The optional Deep Pour Planner uses your entered maximum layer depth. Cost Estimate uses the combined usable kit size and its price. Read the primary resin quantity first, then the A/B split and result details. Copy Resin Plan produces a text reference. Reset returns to a 12 × 8 × 2 inch rectangle, one mold, no displacement, 10% extra and an illustrative 1:1 volume ratio. Entries are local and refresh clears them.

How resin volume is calculated

The calculation follows this order: single-mold geometry → multiply by mold count → subtract total embedded-object displacement → apply extra allowance → split the production quantity into A and B. Equivalently, netBatch = (singleMoldVolume − displacementPerMold) × moldCount; productionVolume = netBatch × (1 + extraPercent / 100).

All dimensions normalize to centimeters and volumes to milliliters before arithmetic. One cubic centimeter is one milliliter. The primary quantity is production volume, while net volume remains visible separately. Extra material does not change the specified mix ratio. The estimate assumes the mold matches its selected ideal geometry and ignores container walls, mold material and objects outside the filled space.

Mold shape formulas

Rectangle

volume = length × width × depth. This is a rectangular prism with straight sides and a uniform base; measure the interior space that will actually be filled.

Round / Cylinder

radius = diameter / 2; volume = π × radius² × depth. Use the full internal diameter, not the radius, in the Diameter field. Tapered vessels require another capacity measurement rather than this constant-cylinder model.

Oval

Oval is modeled as an elliptical cylinder. semiMajor = length / 2; semiMinor = width / 2; volume = π × semiMajor × semiMinor × depth. Length and width are the full axes of the ellipse, not their halves.

Sphere

radius = diameter / 2; volume = 4/3 × π × radius³. This is a full sphere, not a dome or hemisphere. A half-sphere has a different capacity and should use a known Custom Volume rather than silently applying the full-sphere formula.

Custom Volume

Enter the known capacity of one irregular mold in mL, L, US fl oz, US gal, in³ or cm³. Mold count, displacement, extra allowance, A/B splitting and cost still work. A capacity without cross-section geometry cannot produce geometric layer volumes.

Extra resin allowance

productionVolume = netResinVolume × (1 + extraPercent / 100). Presets are 0%, 5%, 10% and 15%, with a custom 0–100% entry. Extra volume = productionVolume − netResinVolume. The allowance can account for material left in measuring and mixing containers or small measurement differences; it is a user-selected allowance, not a guarantee against running short.

The default rectangle needs 106.39 US fl oz net. With 10% extra, mix 117.03 US fl oz, equivalent to 3.461 L. The A/B split and cost use this unrounded production quantity. Layer geometry is labeled separately and does not automatically allocate the extra allowance to each layer.

Object displacement

Embedded objects occupy space that otherwise could contain resin. netSingleMoldVolume = grossSingleMoldVolume − displacementPerMold. For identical molds, both gross capacity and displacement are multiplied by the mold count before allowance is applied.

Enter a measured displacement rather than choosing an invented “small” or “large” object allowance. Displacement must be zero or positive and strictly less than one mold’s gross volume. An equal or larger value removes the resin result. The generic 1,000 mL capacity example with 180 mL displaced needs 820.0 mL net and 902.0 mL with 10% extra. Embedded-object displacement is applied to the total resin estimate, not automatically allocated across individual pour layers.

Part A and Part B mix ratios

For a volume-based A:B ratio a:b and total production volume T, Part A = T × a / (a + b); Part B = T × b / (a + b). The default 1:1 splits T in half. A 2:1 ratio assigns two-thirds to A and one-third to B; 3:1 assigns three-quarters and one-quarter. Custom components are positive numbers and need not sum to 100.

Example default — use your resin manufacturer’s specified ratio. The calculator does not establish a product’s correct formulation. For the default rectangle plus 10% extra at 2:1 by volume, A is 78.02 US fl oz and B is 39.01 US fl oz. The unrounded components sum to the total; separately rounded display values can differ slightly when added.

Volume ratio vs weight ratio

Use the ratio basis specified by your resin manufacturer. A 2:1 volume ratio is not necessarily the same as a 2:1 weight ratio. Fluid ounces measure volume; avoirdupois ounces measure mass. Neither 1 mL = 1 g nor 1 fl oz = 1 oz by weight is assumed for resin.

In this mold-volume workflow, selecting By weight requires a supplied mixed resin density ρ in g/mL or g/cm³. Total target mass M = productionVolume × ρ; Part A mass = M × a / (a + b); Part B mass = M × b / (a + b). Missing density prevents a weight split and copying. The density is blank by default and must describe the relevant mixed material.

This supplies a target total mass and splits that mass at the manufacturer’s weight ratio. It does not convert a volume ratio into a weight ratio. Separate component densities are not inferred, and the calculator does not derive individual component volumes from a weight split. Weight-priced kits require the same explicit mixed density to compare the mold-volume requirement with kit mass.

Deep-pour planning

numberOfPours = ceil(totalDepth / maximumDepthPerLayer). The total-depth field is the same depth used in rectangle, cylinder or oval geometry; editing either depth field updates both. The maximum is entered from your product documentation and is blank until you supply it. The planner is based on the maximum pour depth you entered, not a universal resin depth recommendation.

Layers are maximum-depth chunks plus a final remainder. A 4 in total with a 2 in entered maximum gives 2 + 2 in. A 5 in total gives 2 in, 2 in, 1 in — three pours, without replacing them with equal 1.67-inch layers. Each layer’s gross volume = crossSectionArea × layerDepth, and its gross batch volume multiplies by identical mold count.

Embedded-object displacement is applied to the total resin estimate, not automatically allocated across individual pour layers. Layer volumes use gross geometry before object displacement and extra allowance, so they are not the final net production recipe for each layer. Layer-volume planning for spherical molds is not available in this version. A sphere’s cross-section varies with height, so multiplying its total volume by a depth fraction would be wrong. Custom Volume also lacks the geometry needed for layer volumes.

Use manufacturer instructions for mix ratio, maximum pour depth, working conditions and cure schedule. Actual product constraints can depend on more than depth. No cure timing, working-condition prescription or pour suitability guarantee is produced.

Resin cost estimate

For a kit’s combined usable volume K and price P: costPerVolume = P / K; estimatedResinUsed = productionVolume × costPerVolume; kitsToBuy = ceil(productionVolume / K); leftover = kitsToBuy × K − productionVolume. Purchase cost = kitsToBuy × P. “Estimated resin used” values the consumed material; it is distinct from the cost of buying whole kits.

If a kit is priced by combined usable weight, supplied mixed density converts the production volume to total mass before the same arithmetic is applied in grams. Missing density prevents this comparison. A volume-based mix ratio does not by itself justify comparing a volume requirement with a weight-priced kit.

Kit size must mean usable combined A + B material at the product’s specified ratio. Enter your currency label without fetching exchange rates. The estimate excludes tax, shipping and losses beyond the selected allowance. Zero price is accepted for a no-charge material estimate; kit size must remain positive.

For product pricing, compare selling price with entered unit costs after reconciling resin consumed, whole-kit purchasing and other per-unit expenses. Resin volume or material cost alone is not complete production cost or final profit.

Units

Dimensions support inches, centimeters and millimeters: exactly 1 in = 2.54 cm and 1 mm = 0.1 cm. Canonical volume is mL, with 1 cm³ = 1 mL. One cubic inch is 2.54³ = 16.387064 mL. Custom capacity, displacement and kit volume each have their own volume unit selector and retain canonical values when units switch.

Useful output equivalents always include US fl oz, mL, L and US gal. Exact constants are 1 US fl oz = 29.5735295625 mL and 1 US gal = 3785.411784 mL = 3.785411784 L. US liquid units are explicitly labeled; imperial gallons and fluid ounces are not modeled. NIST’s tables may print rounded factors, while the implementation retains the full conversion constants specified here.

Mass units for weight-priced kits are g, kg, oz by weight and lb. They are never treated as fluid units. Density units g/mL and g/cm³ are numerically equivalent. Calculations retain full floating precision; volumes normally display two decimals, mL one, liters three, and costs two. Tiny positive values are labeled below display precision rather than rounded to a misleading zero.

Worked examples

A 12 × 8 × 2 inch rectangle

The engine gives 192 in³ = 3146.316288 mL, approximately 3,146.32 mL, 3.146 L and 106.39 US fl oz. It is 0.83 US gal.

The same mold with 10% extra

106.39 US fl oz net × 1.10 gives 117.03 US fl oz, or 3,460.9 mL production volume. The extra is applied after any displacement.

A 2:1 volume mix

Using that unrounded production quantity, Part A is 78.02 US fl oz and Part B is 39.01 US fl oz. These are volume amounts, not weight ounces.

A 5 inch deep rectangle with an entered 2 inch maximum

The 12 × 8 inch cross-section gives 3 layers: 2 in → 3,146.3 mL gross per mold; 2 in → 3,146.3 mL gross per mold; 1 in → 1,573.2 mL gross per mold. The last layer is the actual remainder.

Measured displacement in a known capacity

A 1,000 mL custom mold minus 180 mL displacement gives 820.0 mL net. Adding 10% yields 902.0 mL. All five examples are generated from the same engine as the interactive calculator.

Assumptions and limitations

The model assumes ideal straight-sided rectangle, circular cylinder or elliptical cylinder geometry, or a full sphere. It does not infer taper, irregular cross-sections, wall thickness, resin shrinkage, cure behavior, evaporation or an object’s displacement from its appearance. Use a measured Custom Volume when the selected ideal shape is unsuitable.

Dimensions are bounded to 0.000001–100,000 cm equivalent; calculated single-mold volume to 0.000001–1,000,000,000,000 mL; production batch to 10,000,000,000,000,000 mL. Count is an integer 1–10,000, allowance 0–100%, custom ratio components 0.000001–1,000,000 and supplied density 0.000001–1,000 g/mL. These are finite arithmetic bounds, not recommended project sizes or product properties. Layer planning is bounded to 1,000 layers.

Kit price is 0–1,000,000,000 in the entered currency. Numeric drafts are limited to 32 characters and currency labels to 12 plain characters. Invalid active geometry, displacement, ratio, density or enabled optional fields removes the production plan and disables copying. Inactive drafts are retained without being substituted into an active calculation.

Use manufacturer instructions for mix ratio, maximum pour depth, working conditions and cure schedule. There is no resin-brand database, universal ratio, universal maximum depth, cure-time schedule or assurance that a particular pour is suitable. Sources provide terminology and context and do not endorse BuzCalculator.

FAQ

How do I calculate how much resin I need?

Calculate or enter one mold’s capacity, subtract displacement per mold, multiply by identical mold count and add the selected extra allowance. The result is mixed resin volume.

How do I calculate resin for a rectangular mold?

Multiply internal length × width × filled depth in consistent units. The calculator converts inches, centimeters or millimeters to canonical centimeters before calculating volume.

How much extra resin should I mix?

Choose an allowance appropriate to your measured project and product instructions. The presets are arithmetic options, not universal recommendations or a guarantee against running short.

How do I subtract objects embedded in the mold?

Open Objects inside mold and enter measured displacement per mold. It must be below that mold’s capacity. The calculator multiplies it by mold count before applying extra resin.

How do I calculate Part A and Part B?

For ratio a:b, split the total into a/(a+b) and b/(a+b). Confirm whether the manufacturer specifies volume or weight, and use that same basis.

Is a 2:1 resin ratio by volume or by weight?

That depends on the product’s documentation. The selector makes the basis explicit; equal numeric ratios with different bases are not automatically equivalent.

Can I convert resin volume directly to weight?

Only with supplied density information. This version requires a documented mixed resin density for a weight-based split or weight-priced kit and does not assume water-like density.

How does the deep-pour planner work?

It rounds total depth divided by your entered maximum layer depth up, then uses maximum-depth chunks plus a remainder. Gross layer volumes are available only for constant cross-section shapes.

Why does maximum pour depth depend on the resin product?

Product formulation and documented application conditions vary. Enter the limit that applies to your product and project; the calculator does not choose a universal depth or predict curing.

How do I estimate resin cost for a project?

Enter combined usable kit size and price. The estimate values production material used, rounds kit purchases up and shows leftover. Weight-priced kits additionally require mixed density.

Sources

Reviewed October 3, 2026. NIST supplies conversion and density-unit terminology. WEST SYSTEM illustrates manufacturer-specified ratio bases; TotalBoat illustrates product-specific pour-depth context. Product values are not imported as presets, and no source endorses this calculator.

• NIST — volume, length and density unit conversions (opens in a new tab)
• WEST SYSTEM — manufacturer mix-ratio bases (opens in a new tab)
• TotalBoat — product-specific pour-depth context (opens in a new tab)