1Plan a pour
Use mold, casting or coating dimensions—or a measured cavity volume—to calculate how much mixed epoxy the project needs.
Ultimate Epoxy Resin Volume & Mix Calculator
Free maker planning tool
Work out how much epoxy to mix without guessing
Measure the space you want to fill, or enter a total amount you already know. The calculator works out the mixed epoxy needed and splits Part A and Part B using the ratio and measurement basis printed on your epoxy label.
2Split a known total
Already know the amount to mix? Enter the total and the A:B ratio to get exact Part A and Part B shares.
Important: epoxy mix ratios are product-specific. A ratio written by volume is not automatically the same ratio by weight. Always copy the basis from the manufacturer’s current label or technical data sheet.
Molds, castings & coatings
Calculate the resin amount, then split Part A and Part B
Use the project measurements you have, then copy the A:B ratio and whether it is by volume or by weight from your epoxy label.
1
What do you want to calculate?
Start from project measurements, or split a total amount you already know.
2
What space are you filling?
Measure the inside cavity or the actual area you want to coat—not the outside of the mold.
Use 1 for a single mold or pour.
A true hemisphere: height equals half the diameter.
Measure flat side to opposite flat side.
Enter the actual cured layer thickness you intend to pour.
Use a known mold capacity or measure an appropriate empty mold, then dry it fully before epoxy.
2
How much mixed epoxy do you need?
Use this when another plan, mold specification or tested recipe already gives you the total amount.
3
Copy the A:B ratio from your epoxy
The label or technical data sheet should say both the ratio and whether to measure it by volume or by weight.
Optional: enter the mixed density from your product data sheet if you also want an estimated total weight.
4
Optional planning details
Add only the details that apply to your project or epoxy product.
Calculation guide
How to calculate epoxy resin volume and mix ratios
The calculator separates two jobs that are often confused: first find the physical space to fill, then split that mixed amount using the manufacturer’s A:B ratio on the correct measurement basis.
Find the mold, casting or coating volume
Use inside dimensions. In metric, 1 cubic centimeter equals exactly 1 milliliter.
The geometry result is the theoretical space your liquid epoxy must occupy. For multiple identical cavities, multiply one cavity by the quantity. If a known insert displaces resin, subtract its measured volume before adding any mixing allowance.
| Project shape | Measurements | Volume formula |
|---|---|---|
| Box / tray | Inside length, width, fill depth | L × W × D |
| Cylinder | Inside diameter and height | π × (diameter ÷ 2)² × height |
| Sphere | Full diameter | 4/3 × π × radius³ |
| Oval / ellipsoid | Full length, width, height | 4/3 × π × (L/2) × (W/2) × (H/2) |
| Hemisphere / dome | Full diameter | 2/3 × π × radius³ |
| Regular hexagon | Width across flat sides, depth | (√3 ÷ 2) × width² × depth |
| Rectangular pyramid | Base length, base width, full height | L × W × H ÷ 3 |
| Cone | Base diameter and full height | π × radius² × height ÷ 3 |
| Ring / annulus | Outer diameter, inner diameter, height | π/4 × (outer² − inner²) × height |
| Surface coating | Length, width, intended thickness | L × W × thickness |
| Measured cavity | Known or measured capacity | Use the measured volume directly |
Worked example: 4 × 4 × 0.5 in rectangular mold
Geometric volume8 in³
Converted volume131.10 mL
5% planning allowance6.56 mL
Total to prepare137.65 mL
At a true 1:1 ratio by volume, that total splits to about 68.83 mL Part A + 68.83 mL Part B.
Use the A:B ratio on the basis printed on your epoxy
“1:1,” “2:1,” or “100:44” is incomplete unless you also know whether the manufacturer means volume or weight.
Ratio numbers describe shares of a total. If Part A is A parts and Part B is B parts, divide each part count by A + B. Do not convert a volume ratio into a weight ratio just because you own a scale; Part A and Part B can have different densities.
Part A shareTotal amount × A ÷ (A + B)
Part B shareTotal amount × B ÷ (A + B)
2:1 examplePart A = 2/3 of total · Part B = 1/3
100:44 examplePart A = 100/144 · Part B = 44/144
Why the calculator asks for density: geometry produces a volume. If your epoxy must be mixed by weight, the calculator needs the manufacturer’s mixed density/specific gravity to convert the physical cavity volume into grams before it can split that weight correctly.
Calculate coatings from thickness—not a universal “ounces per square foot” shortcut
A coating’s physical volume is area × intended thickness. Product coverage can still differ because real surfaces absorb, drip or vary in level.
Rectangular coatingLength × width × coating thickness
1 ft² at 1/8 in18 in³ = about 294.97 mL = 9.97 US fl oz
This is why the old blanket shortcut of “3 fl oz per square foot for a 1/8-inch coat” was removed: 3 fl oz spread over 1 ft² is only about 0.038 inch thick, not 1/8 inch. Enter the layer thickness you actually intend to pour, then compare the result with the coverage and maximum layer guidance for your exact product.
Round tabletop? Use Cylinder mode with the tabletop diameter and coating thickness as the height. River channel? Use Box/Tray for a regular channel, or break an irregular river into measured sections and add their volumes.
Plan the pour around the epoxy product—not around the mix ratio
A 2:1 ratio does not automatically mean “deep pour,” and a 1:1 ratio does not automatically mean “tabletop resin.”
- 1Copy the exact ratio and basis
Use the current label or technical data sheet for the exact Part A and Part B product.
- 2Check maximum layer depth
If the manufacturer gives a maximum single-pour thickness, enter it under Optional planning details. The calculator can flag when the project is deeper.
- 3Check maximum batch size and pot life
Large mixed masses can heat faster. A product’s allowed batch size and working time come from its manufacturer, not from the A:B ratio alone.
- 4Use a measured cavity when geometry is unreliable
For a suitable irregular empty mold, use a known capacity or measure it with an appropriate liquid, then dry the mold completely before epoxy.
Next step: if the same mold will also be used for candles, compare its capacity with the Water-to-Wax Volume Converter or plan a regular mold with the 3D Candle Mold Wax Calculator. Resin density and wax density are different calculations.
Beginner questions
Epoxy resin calculator FAQs
These answers explain the measurements and limits behind the calculator without replacing the instructions for your exact epoxy product.
How much epoxy resin do I need for a mold?
Use the mold’s inside cavity dimensions, choose the closest shape, and enter the fill depth. The calculator converts the geometric space to milliliters and US fluid ounces, multiplies it by the number of identical pieces, subtracts any known insert displacement, and then adds the mixing allowance you choose.
Should I measure Part A and Part B by weight or by volume?
Use whichever basis the manufacturer specifies for that exact epoxy. A ratio printed by volume should be measured as volume; a ratio printed by weight should be measured on a scale. The two ratios are not automatically interchangeable because Part A and Part B can have different densities.
Can I use a digital scale for a 1:1 epoxy?
Only if the product gives a 1:1 weight ratio. If the label says 1:1 by volume, equal grams may be off-ratio. Check the current label or technical data sheet before switching measurement methods.
How do I calculate a 2:1 or 3:1 resin mix?
For 2:1, there are three total parts: Part A is 2/3 of the total and Part B is 1/3. For 3:1, there are four total parts: Part A is 3/4 and Part B is 1/4. Enter the same ratio basis—volume or weight—that your product specifies.
Can I enter a custom ratio such as 100:44 or 100:30?
Yes. Enter 100 for Part A and 44 for Part B, for example. The calculator normalizes any positive A:B numbers. The important part is copying the exact ratio and its measurement basis from the manufacturer.
Why does Plan a Pour ask for density when my ratio is by weight?
Mold dimensions calculate a volume. A by-weight recipe needs a total mass before it can split grams between Part A and Part B. Mixed epoxy density or specific gravity from the product data sheet provides that conversion. The calculator does not assume a universal epoxy density.
What density should I enter for epoxy resin?
Use the mixed density or specific gravity published for your exact product when available. Do not copy a generic 1.1 g/mL value just because another epoxy uses it. Different formulations and fillers can change density enough to matter when you are converting a cavity volume into a weight-based batch.
How much epoxy do I need for a 1/8-inch tabletop coat?
Enter the surface length, width and 0.125 in coating thickness. Pure geometry says 1 square foot at 1/8 inch thick holds about 294.97 mL or 9.97 US fl oz. Real product usage can be higher on porous or uneven surfaces, around edges, or where resin drips off the workpiece.
Is 3 fluid ounces per square foot really a 1/8-inch epoxy coat?
No. Three US fluid ounces spread evenly over one square foot is only about 0.038 inch thick. The calculator therefore asks for the actual coating thickness instead of using one blanket “ounces per square foot” shortcut.
How do I calculate resin for a round tabletop or coaster?
Use Cylinder mode. Enter the inside or coated diameter and use the pour/coating thickness as the height. The calculator uses π × radius² × height.
How do I calculate resin for an irregular silicone mold?
Use Measured volume when a simple geometry shape does not represent the cavity well. Enter a known capacity, or—only when the empty mold is suitable for it—measure the cavity with water or another appropriate liquid and dry the mold completely before adding epoxy.
Can I use the water method for every resin mold?
No. Use it only when water will not damage, swell, contaminate or become trapped in the empty mold. Silicone molds are commonly suitable, but the mold must be completely dry before epoxy. If water is not appropriate, use a manufacturer capacity or another safe measuring method.
How much extra resin should I mix?
The calculator starts with a 5% planning allowance for resin left on cups and tools, but that is not a universal rule. Set it to 0% for pure geometry or replace it with a percentage measured from your own process. Porous substrates and complex pours may need a different allowance.
Can I calculate several identical molds at once?
Yes. Enter the number under How many identical pieces? The calculator multiplies the net volume of one cavity by that quantity before adding the mixing allowance.
How do I subtract flowers, wood, stones or another insert from the resin volume?
If you know how much liquid volume one insert displaces, enter it under Insert / displacement per piece. The calculator subtracts that volume from each identical cavity. Do not guess a displacement value when the insert volume is unknown.
Does a 2:1 ratio mean the epoxy is safe for a deep pour?
No. Mix ratio and maximum pour depth are separate product specifications. Some deep-casting products may use 2:1, but the ratio itself does not prove a safe layer depth. Follow the maximum single-pour thickness, batch size, ambient-temperature and pot-life guidance for the exact epoxy.
Why can epoxy get very hot, smoke or crack in a large batch?
Epoxy curing releases heat. A large mixed mass or layer that exceeds the product’s limits can build heat quickly. Use the manufacturer’s maximum batch and pour-depth instructions, suitable PPE and workspace guidance. If a mix begins overheating unexpectedly, prioritize personal safety and follow the product’s safety data and emergency instructions.
How does the calculator handle maximum pour depth or maximum batch size?
Open Optional planning details and enter the limits published for your epoxy. If the project is deeper than the layer limit, the calculator estimates the minimum number of staged pours by depth. If the total mix is larger than the batch amount entered, it estimates the minimum number of separate mixes. Curved and tapered shapes may use different resin volumes in equal-depth layers.
Can this calculator tell me the exact number of epoxy layers for a sphere or pyramid?
It can flag the minimum number of layers needed to stay under a depth limit, but equal-depth slices of a sphere, cone or pyramid do not contain equal volumes. Use the result as a pour-planning warning and follow the product’s staged-pour instructions rather than assuming every layer needs the same amount.
Does the calculator work for UV resin, polyester resin or polyurethane?
The geometry formulas can estimate physical volume for many liquids, but the Part A/B workflow is designed for two-part epoxy. UV resin is normally single-part, and other resin chemistries can have different mixing, shrinkage, cure and safety requirements. Use product-specific instructions.
From resin volume to your next mold project
Use the same careful measuring habits when you plan candle wax, mold capacity, fragrance, wicks and production costs.