Epoxy Resin Calculator
Mixing too little epoxy halfway through a pour leaves ridges and dry patches, while mixing far too much wastes an expensive material. This calculator works out the volume needed for a flat rectangular surface from its length, width, and the thickness of the coat you want, then adds a waste allowance for what stays in the cup and on your tools. It reports the result in cubic inches and in U.S. fluid ounces, the units most epoxy products are sold and measured in, so you can buy and mix with confidence.
Epoxy resin formula
area = length * width (square inches)
volume = area * thickness (cubic inches)
fluid ounces = cubic inches / 1.804688
with waste = fluid ounces * (1 + waste% / 100)
One U.S. fluid ounce equals 1.804688 cubic inches, a fixed unit definition. Keeping every length in inches means the area and volume come out in square and cubic inches directly.
Epoxy pour facts
- A flood or seal coat is commonly about one-eighth inch thick; deep pours are built in layers to manage curing heat.
- Two-part epoxy must be mixed in the exact resin-to-hardener ratio the manufacturer specifies.
- Some resin always remains in the mixing cup and on tools, which the waste allowance covers.
- Mixing too thick a layer at once can cause overheating, yellowing, or cracking.
- One U.S. gallon of epoxy is 128 fluid ounces; divide ounces by 128 to estimate gallons.
Epoxy resin: frequently asked questions
How do I work out how much epoxy resin I need?
Multiply the surface length by the width to get the area, then multiply by the desired coat thickness to get the volume. Keeping all measurements in inches gives cubic inches, which convert to fluid ounces by dividing by 1.804688. A waste allowance covers what clings to the cup and brush.
How thick should an epoxy coat be?
A thin seal or flood coat is often around one-eighth of an inch (0.125 in). Deep pours for river tables can be much thicker but usually must be built up in layers because thick epoxy generates heat as it cures. Always follow your specific resin manufacturer's maximum pour depth.
Why does the calculator add a waste allowance?
Some resin always stays behind in the mixing cup, on the stir stick, and on application tools, and a thin pour can need topping up at the edges. A 10 percent allowance is a common starting point, but you can change it. Running out mid-pour risks an uneven, ridged surface.
How do I mix two-part epoxy correctly?
Two-part epoxy has a resin and a hardener that must be combined in the exact ratio printed on the product, by volume or by weight as specified. This calculator gives the total mixed volume you need; split it according to your product's ratio, for example a 1 to 1 ratio means equal parts of each.
Does this work for round or irregular surfaces?
This calculator assumes a flat rectangle. For a circle, compute the area separately (pi times radius squared) and multiply by thickness. For irregular shapes, break the surface into rectangles and add the volumes. The thickness-to-volume conversion is the same in every case.
Official sources
- National Institute of Standards and Technology (NIST): Unit conversion reference.
- NIST Handbook 44: Specifications for weighing and measuring devices (volume units).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.