How epoxy volume is calculated
The math is straightforward geometry plus one unit conversion, following the method used byTotalBoat’s official epoxy calculator:
| Step | Formula |
|---|---|
| Rectangular volume | Length × Width × Thickness (in³) |
| Circular volume | π × (Diameter ÷ 2)² × Thickness (in³) |
| Cubic inches → fluid ounces | in³ ÷ 1.805 = US fl oz |
| Fluid ounces → gallons | fl oz ÷ 128 = US gal |
| Fluid ounces → milliliters | fl oz × 29.5735 = ml |
| Waste margin (optional) | Total × 1.10 |
The result is the volume of mixed epoxy. The calculator then splits that total into resin and hardener according to the volume mix ratio you select. For a 2:1 ratio, resin is 2/3 of the total and hardener is 1/3; for 3:1, resin is 3/4 and hardener is 1/4.
Volume ratio vs weight ratio — read this before using a scale
Epoxy mix ratios printed on the bottle are almost always by volume, and this calculator works in volume too. But resin and hardener do not weigh the same per fluid ounce.West System documents this explicitly for its 105 Resin / 205 Hardener: the ratio is5:1 by volume but 5.19:1 by weight. Pouring a "1:1" product onto a kitchen scale in equal grams can therefore leave you measurably off-ratio, and off-ratio epoxy cures soft, sticky, or brittle — the reaction is stoichiometric, and excess of either part never fully cures. If you prefer weighing (which is more precise for small batches), find the weight ratio in the manufacturer’s technical data sheet and use that number instead.
Coverage reference values
Published coverage figures used and cited on this page:
| Reference value | Figure | Source |
|---|---|---|
| Cubic inches per fluid ounce | 1.805 in³ = 1 fl oz | TotalBoat epoxy calculator |
| Table-top flood coat coverage at 1/8″ | ≈ 12 sq ft per gallon | TotalBoat |
| Thin sealer coat coverage | ≈ 40 sq ft per pound | West System |
| 1/8″ flow coat usage | ≈ 0.75 lb per sq ft | West System |
| Volume vs weight ratio example | 5:1 volume = 5.19:1 weight | West System 105/205 |
Worked example
A 36″ × 18″ table top gets a 1/8″ (0.125″) flood coat: 36 × 18 × 0.125 = 81 in³. Converting, 81 ÷ 1.805 = 44.9 fl oz (about 1,327 ml, or 0.35 gal). With a 10% waste margin that becomes 49.4 fl oz, and at a 1:1 ratio you would measure out roughly 24.7 fl oz of resin and 24.7 fl oz of hardener. Cross-checking against TotalBoat’s coverage figure: 4.5 sq ft at 1/8″ against ~12 sq ft/gal predicts ~0.37 gal — the two methods agree.
Tips for a successful pour
Measure parts separately and accurately — eyeballing is the top cause of cure failures. Mix thoroughly for the full time the manufacturer specifies, scraping the sides and bottom of the cup, and consider transferring to a second cup ("double-cup" method) for critical clear castings. Warm resin (around 75 °F) flows and de-gasses better than cold resin. Level the workpiece before pouring, seal porous surfaces like wood with a thin seal coat first to reduce bubbles, and respect your product’s maximum pour depth to avoid an exothermic runaway. Mixed epoxy left in a bulky cup heats faster than epoxy spread thin, so pour promptly after mixing.
Frequently Asked Questions
How do I convert cubic inches of epoxy to fluid ounces?
Divide cubic inches by 1.805: in³ ÷ 1.805 = US fl oz. This is the conversion used by TotalBoat's official epoxy calculator. From there, fl oz ÷ 128 = US gallons, and fl oz × 29.5735 = milliliters.
Is a 1:1 mix ratio by volume the same as 1:1 by weight?
No. Resin and hardener have different densities, so volume ratios and weight ratios differ. West System, for example, specifies a 5:1 ratio by volume that corresponds to 5.19:1 by weight for its 105/205 system. Always check the manufacturer's technical data sheet for the correct weight ratio if you are measuring on a scale.
How much extra epoxy should I mix?
Mixing about 10% extra is a common rule of thumb to cover cup residue, brush loss, uneven surfaces, and drips over edges. This calculator has a checkbox that adds the 10% margin for you. Running out mid-pour is far worse than a little waste — a seam between batches can show in clear castings.
How thick can I pour epoxy in one layer?
It depends entirely on the product. Table-top / coating epoxies are typically designed for thin pours around 1/8″ per coat, while dedicated deep-pour casting resins allow 1–2″ or more per pour. Exceeding the rated depth traps exothermic heat, which can cause yellowing, cracking, or smoking. Check your product's maximum pour depth.
How much area does a gallon of epoxy cover?
At a 1/8″ flood-coat thickness, one US gallon of table-top epoxy covers roughly 12 square feet (per TotalBoat's coverage guidance). Thinner seal coats stretch much further — West System quotes about 40 sq ft per pound for a thin sealer coat.
Does the calculator account for the volume of objects embedded in the pour?
No — it computes the full volume of the shape you enter. If you are encapsulating objects (wood, flowers, electronics) or filling around a river-table void, subtract the approximate volume of the solid material, or simply treat the result as an upper bound and mix slightly less plus a reserve batch.