Epoxy Resin Calculator

How Much Epoxy Do You Actually Need?

Running short mid-pour is the most expensive mistake in resin work. A second batch mixed to top up a curing pour almost never matches — different mix, different temperature, a visible seam, wasted material. The fix is thirty seconds of math before you touch a cup. Every epoxy calculation follows the same chain: volume → mixed resin → resin/hardener split → buffer. Get the volume right and everything downstream is arithmetic.

The core formulas depend on shape:

• Rectangular mold or coating: length × width × depth. A 60 × 45 cm tabletop with a 0.3 cm flood coat needs 60 × 45 × 0.3 = 810 ml of mixed resin.
• Round mold or tray: π × radius² × depth. A 30 cm diameter tray poured 0.6 cm deep: 3.14 × 15² × 0.6 = 424 ml.
• Any irregular mold — the water trick: fill the mold with water, weigh the water in grams, and multiply by 1.1. Resin is denser than water, so 196 g of water ≈ 216 g of mixed epoxy. Fast, and it automatically accounts for every curve of the mold.

Remember that 1 cm³ = 1 ml, so working in centimeters gives milliliters directly — the unit most resin kits are measured in.

Memorize These Coating Numbers

If you coat tabletops regularly, two numbers save constant recalculation. A standard 1/8-inch (0.3 cm) flood coat needs about 12 fluid ounces per square foot (≈ 355 ml). A thin 1/16-inch seal coat needs about 6 oz per square foot. A seal coat first is not optional on porous wood — it locks down air that would otherwise rise as bubbles into your flood coat.

Mix Ratios: Volume vs Weight

Epoxy is a two-part system: resin (Part A) plus hardener (Part B), and the ratio is chemistry, not suggestion. Common systems are 1:1 (often tabletop/coating resins), 2:1 (many art and casting resins), and 3:1 (some deep-pour systems). The critical question: ratio by volume or by weight? They differ because resin and hardener have different densities. A "2:1 by volume" system is not 2:1 by weight.

Always follow your product's data sheet. If it says by volume, measure in graduated cups; if by weight, use a scale (more accurate). This calculator splits by volume parts: for a 2:1 system, resin = total × 2/3, hardener = total × 1/3. For 810 ml at 2:1: 540 ml resin + 270 ml hardener. Being off-ratio is the #1 cause of sticky, never-curing pours — measure like a pharmacist, not a cook.

The 10–15% Buffer Rule

Calculated volume is theoretical volume. Reality adds: resin clinging to mixing cups and sticks, slight mold flex, and the fact that a short pour can't be fixed. Professionals add a 10–15% buffer to every calculation. On a 1-liter pour that's 100–150 ml of insurance — far cheaper than a ruined project. This calculator applies your chosen buffer before splitting the ratio, so the A/B numbers already include it.

Deep Pour vs Coating: Different Resins, Different Rules

Epoxy curing is exothermic — it generates heat. Thin coatings shed heat easily; thick pours trap it, and trapped heat accelerates the cure, which generates more heat — a runaway that cracks, yellows, or even smokes. That's why there are two resin families:

Coating resins cure fast and hard but must stay under ~6 mm per pour. Deep-pour resins cure slowly (24–72 hours vs 12–24) and can go 2–5 cm per pour depending on the product. Never use a coating resin for a deep pour — the data sheet's maximum pour depth is a hard limit, not a suggestion. The layer planner in this calculator divides your total depth by the max depth to tell you how many pours the project needs; let each layer reach a firm gel before the next.

Mixing: The Three-Minute Rule

Bad mixing causes more failures than bad measuring. Scrape the sides and bottom of the cup continuously — unmixed resin hiding in the corners is what leaves soft spots. Mix for a full 3 minutes (longer for large volumes), then consider the two-cup method: pour the mixed batch into a second clean cup and stir another minute, leaving any unmixed residue behind in cup one. The mixture should go completely clear and streak-free; any cloudy ribbons mean keep stirring.

Bubbles: Prevention Beats Removal

Bubbles come from three sources: air folded in during mixing, air released from porous substrates, and outgassing as the resin warms. Prevention: warm the resin bottles in warm (not hot) water before mixing to lower viscosity, stir slowly without whipping, seal porous wood first, and pour in a warm room — cold resin is thick resin, and thick resin traps bubbles. After pouring, a quick pass with a heat gun or torch held 15–20 cm away pops surface bubbles; keep it moving to avoid scorching. Deep bubbles in thick pours may need a second pass 10 minutes later.

Cure Times and When It's Really Done

"Dry to the touch" is not "cured." Typical timelines at ~22°C: tabletop resins — tack-free in 6–12 hours, light use in 24–72 hours, full cure in 7 days. Deep-pour resins — 24–72 hours to demold, full cure in 7–14 days. Cold rooms slow everything dramatically; below ~18°C some systems barely cure at all. Don't rush demolding — a piece demolded soft can warp as it finishes curing. And keep fresh pours dust-free: a cardboard box over the project is the classic studio solution.

Safety: Non-Negotiable Gear

Uncured epoxy is a sensitizer — repeated skin contact can develop into a permanent allergy that ends your resin hobby. Nitrile gloves always (latex dissolves), respirator with organic-vapor cartridges when mixing large volumes or sanding, eye protection, and ventilation. Sand cured resin wet or with extraction — the dust is the hazard. Keep isopropyl alcohol nearby for cleaning tools and drips, and never pour excess resin down drains; let it cure in the cup and bin it.

Troubleshooting Common Failures

Sticky or soft spots after full cure time

Off-ratio mix or incomplete mixing — the two classic causes. There's no fix except removing the soft area and re-pouring; prevention (scale, 3-minute mix, two-cup method) is everything.

Amine blush (waxy film on surface)

Some hardeners form a blush in humid conditions. Wash it off with warm soapy water before sanding or re-coating, or it will cause adhesion failures.

Fish eyes / craters

Surface contamination — silicone, oils, or dust. Wipe substrates with isopropyl alcohol before pouring and keep silicone tools away from pre-pour surfaces.

Yellowing

All epoxy yellows eventually with UV exposure; quality resins include UV stabilizers that delay it for years. For pieces in direct sun, a UV-stable topcoat helps. Excessive heat during cure (too-deep pour) yellows fast — another reason to respect max pour depth.

Cracking

Almost always exothermic runaway from too-deep a pour with the wrong resin, or demolding stress on an under-cured piece. Match resin to depth, pour in layers, control room temperature.

Buying the Right Amount

Resin is sold by kit size (1L, 4L, 20L…), and kits are cheaper per liter — but resin has a shelf life of roughly 12 months unopened, less once opened. Size your purchase to the project plus buffer, not the bargain: a 20L kit that half-cures in the bottle is no deal. Calculate the project (this page), add the buffer, check your ratio split, and buy the smallest kit that covers it with a little headroom. Your future self, mid-pour with exactly enough resin, will thank you.