Epoxy Calculator: How Much Resin Do You Need?
Enter your surface dimensions, desired coating thickness, and mix ratio to instantly find out how many fluid ounces, gallons, or liters of epoxy you need, split into Part A and Part B. Toggle between a single flood coat and a seal coat plus flood coat combo. Supports 1:1 and 2:1 mix ratios, rectangular and circular surfaces, and both metric and imperial units.
How to calculate how much epoxy you need
The core formula is straightforward: multiply your surface area (in square inches) by the desired coating thickness (in inches) to get the volume in cubic inches, then divide by 1.805 to convert to fluid ounces. One gallon of mixed epoxy equals 128 fluid ounces, so divide again by 128 to get gallons. For a 36 in by 24 in countertop (864 in^2) at 1/8 in (0.125 in) thick, the calculation is 864 in^2 x 0.125 in = 108 in^3, then 108 / 1.805 = about 59.8 fl oz, or just under half a gallon. Always add 10% for waste, giving about 65.8 fl oz before rounding up to the next available kit size.
Seal coat vs. flood coat: which do you need?
A seal coat (also called a prime coat or saturation coat) is a thin first layer, typically 6-10 mils (0.006-0.010 in), applied to porous surfaces like raw wood, concrete, or MDF. Its job is to fill the pores and prevent air from escaping during the thicker flood coat, which would create bubbles. You brush or roll it on, let it become tacky (usually 3-5 hours), and then pour the flood coat while it is still in the gel window so the two layers chemically bond. Sealing is essential on unfinished wood and optional on already-sealed or non-porous surfaces. The flood coat is the main, self-leveling layer that creates the smooth, glassy final surface, typically poured at 1/8 in for a bar or countertop. If you skip the seal coat on bare wood, trapped air will create bubbles you cannot remove once the epoxy cures.
Mix ratio: why it matters and how to get it right
Epoxy is a two-part system: Part A (resin) and Part B (hardener, also called catalyst or activator). The ratio by volume on the label, such as 2:1 or 1:1, is not a suggestion. If you add too little hardener, the epoxy will remain soft, tacky, or never fully cure. Too much hardener and the excess cannot react, leaving the surface similarly compromised. Always measure by volume using graduated mixing cups or, for more accuracy, by weight using a digital scale and the manufacturer weight ratio, which differs from the volume ratio. Mix thoroughly for 3-5 minutes, scraping the sides and bottom of the container. Then transfer to a clean cup and mix for another 1-2 minutes to avoid any unmixed material from the container walls. Pour immediately once mixing is complete.
Deep pour vs. coating epoxy: choosing the right product
Standard coating epoxy is designed to be poured at 1/8 in to 1/4 in per coat. If you try to pour it thicker than that, the exothermic chemical reaction generates so much heat that the epoxy can crack, yellow, or even smoke. Deep-pour casting epoxy (also called river-table epoxy) uses a slower-curing formula that releases heat more gradually, allowing pours of 1 to 2 inches or more in a single layer. If your target thickness is above 1/4 in in one pour, you must use a product rated for that depth. For thicknesses between 1/4 in and 1 in, you can also do multiple thin coats of standard coating epoxy, each poured while the previous coat is still in its gel window for a chemical bond. Always check the pour-depth specification for your specific product before starting.
Epoxy coverage and application guide
| Thickness | Coverage per gallon | Typical application | Coat type |
|---|---|---|---|
| 1/16 in (1.6 mm) | ~25 ft² | Thin seal prime, fiberglass laminating | Seal / prime |
| 1/8 in (3.2 mm) | ~12-16 ft² | Bar tops, countertops, table surfaces | Flood coat |
| 3/16 in (4.8 mm) | ~8 ft² | Thicker countertop or decorative layer | Flood coat |
| 1/4 in (6.4 mm) | ~6 ft² | Extra thick flood coat, river table edge | Flood coat |
| 1/2 in (12.7 mm) | ~3 ft² | Shallow river table, thick decorative pour | Deep pour |
| 1 in (25.4 mm) | ~1.5 ft² | Standard river table pour depth | Deep pour |
| 2 in (50.8 mm) | ~0.75 ft² | Maximum typical deep-pour thickness | Deep pour |
Approximate coverage rates for standard 1-gallon mixed epoxy at common thicknesses. Actual coverage varies by product, surface porosity, and temperature.
Frequently asked questions
How much epoxy do I need for a countertop?
Measure the length and width in inches and multiply to get square inches. Multiply by 0.125 (for 1/8 in standard thickness) and divide by 1.805 to get fluid ounces. Add 10% for waste. A 96 in x 26 in countertop is 2,496 in^2, giving about 172 fl oz or 1.35 gallons of mixed epoxy before the waste factor, about 1.5 gallons total. If the surface is bare wood, add a seal coat first.
What is the difference between 1:1 and 2:1 mix ratio?
A 1:1 ratio means equal volumes of resin and hardener. A 2:1 ratio means two parts resin to one part hardener by volume. These are different chemical formulations and cannot be swapped. Always follow the manufacturer's label. If you mix the wrong ratio, the epoxy will not cure properly and you will have to remove it and start over.
Why should I add a waste allowance?
When you mix and pour epoxy, some sticks to the mixing container and stir stick, some drips over edges, and porous or uneven surfaces absorb more than flat ones. A 10% allowance is the industry standard for typical projects. Increase to 15-20% for highly porous wood, rough concrete, complex shapes, or if you are mixing multiple small batches (each batch leaves residue in its cup).
How many coats of epoxy does a bar top need?
Most bar tops use a seal coat followed by one or two flood coats, each at 1/8 in. The seal coat stops air bubbles from bare wood. The first flood coat creates the base layer. A second flood coat adds depth and clarity, and can cover any minor imperfections like dust nibs in the first coat. Three total applications (1 seal + 2 flood) is common for a professional finish.
How do I calculate epoxy for a circular table?
Use the circle area formula: Area = pi x radius^2. A 30 in diameter table has a radius of 15 in, so Area = 3.14159 x 15^2 = 706.9 in^2. Multiply by thickness (0.125 in for 1/8 in) to get 88.4 in^3, then divide by 1.805 for about 49 fl oz, or roughly 0.38 gallons. Add 10% waste for about 54 fl oz. This calculator does the full conversion for you.
Can I do one thick pour instead of multiple coats?
It depends on the product. Standard coating epoxies are typically limited to 1/8 in to 1/4 in per pour to avoid overheating. If you need more thickness, either use a deep-pour (casting) epoxy rated for that depth, or apply multiple thin coats while each previous coat is still in its gel window, allowing chemical bonding between layers. Pouring a standard coating epoxy too thick can cause yellowing, cracking, or a runaway exothermic reaction.
How does temperature affect my epoxy calculation?
Temperature affects working time and cure rate, not the volume calculation directly. However, cold surfaces and cold epoxy are more viscous, so they flow less and may cover slightly less area or trap more air. Working below 65 F can prevent curing entirely. Some manufacturers recommend increasing quantity by 5-10% in cold conditions because the epoxy is less fluid and harder to spread evenly. Always work in a 70-80 F environment for best results.