Epoxy Resin Calculator
Work out exactly how much mixed epoxy a pour needs, split into part A and part B for your ratio — for river tables, molds, coasters, tumblers, and flood coats. Running short mid-pour leaves a visible line, so measure once and mix right.
Average the wavy gap width. For a full slab subtraction, use the dedicated River Table calculator.
Advanced: waste & pricing
Formula & how it works
Volume in cubic inches is length × width × depth (a cylinder uses π × r² × height). One US gallon of mixed epoxy fills 231 cubic inches; one fluid ounce fills 1.805 cubic inches.
The calculator adds your waste margin, then divides the total by the mix ratio so you can measure part A and part B directly: part B = total ÷ (ratio + 1), part A = part B × ratio.
Worked example
A rectangular fill 24 × 12 × 0.5 in is 144 in³. With a 10% margin that's 158.4 in³ ≈ 87.8 fl oz. At 2:1, that splits to about 58.5 fl oz resin and 29.3 fl oz hardener.
Getting the pour right
Measure by volume or by weight?
Follow the label. Most hobby epoxies specify ratios by volume, but part A and part B have different densities, so a 1:1 by-volume product is not 1:1 on a scale. Mixing at the wrong ratio is the most common cause of soft, sticky cures — and it cannot be fixed by adding more hardener afterward.
Why did my deep pour crack or yellow?
Epoxy cures exothermically, and thick pours trap that heat. Past the rated depth the center can exceed safe temperature, causing yellowing, cracks, or a violent flash cure. Deep-pour formulas cure slowly and cooler; table-top formulas do not.
Does temperature matter?
Yes. Most resins want the workspace, the resin, and the mold at roughly 72–77°F. Cold resin is thick, holds bubbles, and may never fully cure; a warm water bath for the sealed bottles before mixing helps in winter.