Epoxy Resin Volume & Mix Ratio Calculator

What is The Chemistry & Geometry of Epoxy Casting?

Epoxy resin is an expensive, thermochemical polymer. Calculating the exact volume of resin needed for a river table, mold, or floor coating is critical not just for budget, but to prevent exothermic thermal runaways caused by pouring too much chemical mass at once.

Mathematical Foundation

Volume Geometry (Imperial)

V\ (in^3) = L \times W \times D

D

= Pour depth in inches — measured at the deepest point of the cavity. For river tables, take the average width of the live edge gap.

Fluid Ounces Conversion

Fl\ Oz = V\ (in^3) \times 0.5541

0.5541

= The mathematical constant to shift from cubic solid inches into liquid fluid ounces.

Ratio Distribution (Part A / Part B)

\text{Part B Volume} = \text{Total} \times \left(\frac{\text{Ratio B}}{\text{Ratio A} + \text{Ratio B}}\right)

\text{Ratio B}

= Usually the hardener. In a 2:1 mix, B represents 1 part of the 3 total parts (33.3%).

Laws & Principles

Exothermic Mass Limit: Epoxy creates violent heat when curing. Standard 'Bar-top' epoxies are designed to cure fast and must NEVER be poured thicker than 1/4-inch. Pounding 2 inches of bar-top resin into a mold will cause it to literally boil, yellow, and crack.
The Deep Pour Chemistry: 'Deep Pour' or casting epoxies use a completely different chemical hardener. They cure very slowly over 72 hours, generating minimal heat. This allows them to be poured 2 to 4 inches thick safely.
The 15% Waste Law: Always calculate your perfect mathematical volume, and then strictly add 15%. Mold leaks, surface tension meniscus climbing, and vacuum-chamber degassing will consume more liquid than pure geometry predicts.
Volume vs Weight Ratios: A 2:1 mix ratio 'by volume' is completely different than a 2:1 mix ratio 'by weight'. The hardener (Part B) has a different chemical density than the resin (Part A). Using a kitchen scale for a 'by volume' resin will ruin the chemical setup.

Step-by-Step Example Walkthrough

" Pouring a Walnut River Table that is 72 inches long, has an average river gap of 14 inches, and is 2 inches thick. We are using a Deep Pour 2:1 epoxy. "

1. Find Total Volume: 72 × 14 × 2 = 2,016 cubic inches.
2. Convert to Liquid: 2,016 × 0.5541 = 1,117 fluid ounces of raw epoxy needed.
3. Apply Safety Buffer: 1,117 × 1.15 (15% waste for leaks and edges) = 1,284 fluid ounces.
4. Convert to Gallons: 1,284 ÷ 128 = 10.03 Gallons total required.
5. Split the Mix (2:1): Part A is 2/3rds (6.68 Gallons). Part B is 1/3rd (3.34 Gallons).

Final Result: To execute this pour, the fabricator must purchase exactly four standard 3-Gallon Deep Pour kits (giving them 12 gallons total on hand) to safely handle the 10-gallon volumetric demand.

Quick Answer: How much epoxy resin do I need?

To determine how much epoxy resin you need, measure the exact Length, Width, and Depth of your mold in inches, multiply them together to get Cubic Inches, and multiply by 0.5541 to convert into fluid ounces. For metric, measure in centimeters, multiply L × W × D, and divide by 1,000 to get Liters. Always add a 10% to 15% safety buffer to account for minor mold leaks, surface absorption into dry wood edges, and mixing cup loss.

The Resin Volume Math

Total US Gallons = ((Length × Width × Depth) × 0.5541) / 128

Scaling Variables:

Mold Seal Loss: Even heavily taped forms will seep some liquid during the hours-long thin phase before gelling.
Average Width: For live-edge wood tables, the 'river' constantly changes width. Measure the gap at 10 different points and average them for your 'Width' variable.

Application Type	Standard Ratio	Max Pour Depth
Bar Top / Table Coating	1:1 Volume	1/4 Inch (1/8" ideal)
Casting Molds (Soft)	1:1 Volume	1 to 2 Inches
Deep Pour River Tables	2:1 Volume	2 to 4 Inches
Industrial Floor Coatings	Varies (100% Solids)	Mil thickness

Application Type

Standard Ratio

Max Pour Depth

Bar Top / Table Coating

1:1 Volume

1/4 Inch (1/8" ideal)

Casting Molds (Soft)

1:1 Volume

1 to 2 Inches

Deep Pour River Tables

2:1 Volume

2 to 4 Inches

Industrial Floor Coatings

Varies (100% Solids)

Mil thickness

Chemical Failures & Financial Mistakes

Exothermic Boiling

A hobbyist buys a cheap gallon of 1:1 "Table Top" epoxy because it was half the price of actual Deep Pour resin. They mix it and pour a 2-inch thick river table. Because Table Top resin is engineered to cure instantly in exactly 1/8-inch thickness, the massive 2-inch chemical block traps its own heat. Within 20 minutes, the resin reaches 350°F, boils, cracks the wood, and hardens into a yellowed, smoking mess. The $400 wood slab is permanently ruined.

The 'By Weight' Mixing Disaster

A fabricator is mixing a huge batch of 2:1 Deep Pour resin. Instead of using measuring buckets, they put the bucket on a digital scale and pour 20 lbs of Part A, and 10 lbs of Part B. But this particular brand was specified to be mixed "2:1 By Volume." Part B (Hardener) is significantly lighter chemically than Part A. Because they mixed by weight, they severely over-hardened the mixture. The epoxy kicks instantly in the bucket, turning solid before they can even pour it.

Field Design Best Practices & Pro Tips

Do This

✓Seal Coat the Live Edge. Before doing a massive deep pour computation, physically brush a thin coat of fast-cure epoxy over the rough live edges of the wood and let it dry. Wood is porous; it will "breathe" out trapped air into your deep pour, creating millions of micro-bubbles that get locked in the plastic. Sealing the wood stops this entirely.

Avoid This

✗Never scrape the sides of the mixing cup during a final pour. When mixing Part A and B, you must scrape the walls of the bucket to agitate it. However, when pouring into the final mold, NEVER scrape the bucket out to get the last drops. The resin clinging to the inner plastic walls is often unmixed film. If it lands in your mold, you will have permanent sticky "soft spots" that never cure.

Frequently Asked Questions

How much epoxy for a river table?

It depends entirely on your live edge geometry. Measure in multiple locations to find the average width. A typical dining table with a 2-inch depth and 10-inch average river width running 72 inches will require roughly 7.5 to 8 gallons of resin. Always mix a 10-15% buffer above the math.

What is the difference between 1:1 and 2:1 Epoxy?

1:1 Epoxies are highly reactive, curing very quickly. They are cheap, hard, and exclusively meant for thin coatings (1/8-inch thickness). 2:1 or 3:1 Epoxies use a completely different chemical structure to cure very slowly over several days. This slow cure prevents heat buildup, allowing you to pour massive "Deep Pours" of 3 to 4 inches thick at one time.

Why did my epoxy boil and crack my wood table?

This is exothermic thermal runaway. You poured a fast-curing (1:1 style) tabletop resin too thick. Epoxy does not "dry", it goes through a chemical reaction that generates extreme heat. If poured thick, the resin acts as an insulator, trapping its own heat, causing the temperature to spike abruptly out of control until the chemicals physically boil.

Can I just add more hardener to make the epoxy cure faster?

No. This is not polyester resin or fiberglass bondo. Epoxy requires an exact mathematical molecular match. If you add more hardener into the bucket, it will not find any resin molecules to bond with. The extra hardener will simply stay liquid forever, resulting in a rubbery, sticky casting that completely destroys your project.

Resin Geometry Engine