Epoxy Resin Calculator — Volume, Mix Ratio and Cost

Work out how much epoxy a mould, river table or surface coat needs, split into resin and hardener at your kit’s own ratio, in litres, gallons, fluid ounces and grams — with the pour depth checked against what a single layer can safely take.

Created by Ashar PervaizLast updated 3 November 2026

How Much Epoxy You Actually Need

Every epoxy calculation is the same calculation: work out the volume of the space you are filling, then split that volume into resin and hardener in whatever proportion your kit specifies. Everything else — gallons, litres, fluid ounces, grams, cost — is unit conversion applied afterwards.

Volume = length × width × depth          (rectangular)
Volume = π × (diameter ÷ 2)² × depth     (round)
Volume = area × coat thickness           (surface coat)

The arithmetic is not where projects go wrong. People get the multiplication right and still order the wrong amount, because they measured the wrong space, read the label in the wrong units, or applied a mix ratio that was never meant to be measured the way they measured it. The rest of this page is about those four failures, in roughly the order they cost people money.

A River Table Is the Channel, Not the Table

This is the most expensive measuring mistake in the whole craft, and it is made by people who know perfectly well how to multiply three numbers together. A river table’s resin fills the gap between two live-edge slabs. It does not cover the slabs. So the volume you need is the volume of that channel, and the tabletop’s overall dimensions have almost nothing to do with it.

A channel 60 inches long, averaging 6 inches across and 1.5 inches deep comes to 540 cubic inches, which is 2.34 US gallons or 8.85 litres. The table that channel sits in might be 60 by 36 inches. Work from the table and you would calculate 3,240 cubic inches for the same 1.5-inch depth — six times too much, and several hundred pounds or dollars of resin you will never use.

The word that does the work above is averaging. Live edges are not parallel; that is the entire point of them. Measure the gap at several points along the channel and take the mean, and if the edges are dramatically irregular, measure in sections and add the sections together. A channel that is 4 inches at one end and 10 at the other is not the same as one that is 7 inches throughout, but for volume purposes it is close enough, and the waste allowance covers the difference.

If the table also gets a flood coat across the finished surface, that is a second, separate calculation — switch the tool above to surface coat, run it, and add the two totals.

Coverage, and Why “Twenty Square Feet a Gallon” Is Wrong

For a coating rather than a casting, the question is how far a given volume spreads at a given thickness. This has an exact answer, because the US gallon is defined as 231 cubic inches. Divide that by the thickness and you have the area:

231 ÷ 0.125 in  = 1,848 in²  = 12.83 sq ft per gallon at 1/8"
231 ÷ 0.0625 in = 3,696 in²  = 25.67 sq ft per gallon at 1/16"
231 ÷ 0.25 in   =   924 in²  =  6.42 sq ft per gallon at 1/4"

1 litre ÷ 3 mm = 3,333 cm² = 0.33 m² per litre at 3 mm

Manufacturers quote figures a little below these — 12 square feet per gallon is common against the 12.83 the geometry gives — and they are right to, because the arithmetic assumes every drop lands on the surface and none runs off the edge. What you should be wary of is the opposite direction. Several calculators currently ranking for epoxy coverage quote around 20 square feet per gallon for a 1/8-inch flood coat. That figure corresponds to about a twelfth of an inch. Follow it and you will mix a third less than the job needs, which you discover when the pour stops short of the far edge and the first batch has already started to gel.

Seal coats are genuinely different and genuinely do go much further — they are a thin wetting layer meant to seal porous timber so the flood coat does not bubble, and a gallon can cover three or four times the area. If your project needs both, calculate them separately.

By Weight and By Volume Are Two Different Numbers

Here is the one that ruins batches. A kit might say 2:1 and another might say 100:45, and a reasonable person could assume the second is a strange way of writing the first. It is not. The first is a ratio by volume and the second is a ratio by weight, and they describe the same mix only because resin and hardener have different densities.

Hardener is typically lighter than resin, so two volumes of resin to one of hardener works out at roughly 100 parts resin to 41–45 parts hardener on the scale, varying by brand. A 1:1 system by volume can be near 100:83 by weight. The gap between what you think you are measuring and what you actually are is far larger than the tolerance of the chemistry.

That tolerance is the reason it matters. Most systems will take a deviation of about five per cent before the cure is affected. Measure a 2:1 volume ratio on a scale and you are not five per cent out, you are closer to twenty — and what you get is a casting that stays soft, stays tacky, or hardens unevenly, days after it should have been finished. There is no fixing it afterwards. The piece is scrap.

So: read which basis your kit states, set the tool above to match, and measure on that basis. If the data sheet gives both, use weight, since a scale is unaffected by bubbles, by temperature, or by reading a meniscus from slightly the wrong angle. The one thing never to do is read one and measure the other.

Depth Is the Thing That Burns You

Epoxy cures by an exothermic reaction: it makes heat as it hardens, and heat makes it harden faster, which makes more heat. Whether that runs away depends on how easily the heat escapes, and that is governed by the shape of the pour rather than its size.

A litre of resin spread a millimetre thick over a tabletop has an enormous surface area relative to its volume. The heat leaves as fast as it is made and the cure is gentle. The same litre in a narrow, deep mould has very little surface for its volume, so the heat stays in. That is why maximum pour depths are quoted in inches and not in litres, and why the calculator above asks for your product’s limit rather than assuming one.

As a rough guide, most deep-pour casting resins permit around 2 inches in a single layer and a few permit 4, while standard tabletop and bar top epoxies are formulated for an eighth of an inch at a time. Take the number from the data sheet — this is exactly the figure brands differ on, because it falls out of their specific formulation. Exceed it and the results range from cloudiness, yellowing and trapped bubbles through to cracking, and at the far end a mass hot enough to deform a silicone mould.

When the tool tells you a pour needs several layers, let each one cure to the point the manufacturer specifies before the next goes on, typically while it is still slightly tacky so the layers bond chemically rather than merely sitting on each other.

What the Waste Allowance Is Actually For

Five to ten per cent is the usual range, and it is worth understanding that this is not a safety margin against your own arithmetic. It is an accounting of resin that physically cannot reach the mould: the film clinging to the mixing cup, what stays on the stir stick, what is left in the measuring jug, and on a flood coat, everything that runs over the edge and onto the drip sheet.

That makes the right figure a function of your process rather than your project. Deep moulds with awkward internal shapes hold more back. Pouring in several layers means paying the cup-residue cost on every batch rather than once, so a four-layer pour justifies the top of the range where a single pour does not. Very small batches lose a much larger proportion to the container than big ones — on a 30 ml mix for jewellery, ten per cent may well be optimistic.

Pigment, Mica and the Point of Diminishing Returns

Pigment is measured as a percentage of the mixed resin weight, and the published guidance is genuinely inconsistent. Pigment manufacturers often suggest half a per cent to three per cent of mixed weight for a translucent tint. Calculators aimed at tumbler and coaster makers routinely quote six to ten per cent for full opacity. Both can be right for their own products and purposes.

The principle underneath is more useful than any single number. Pigment takes no part in the curing reaction. Every gram you add is a gram of inert material suspended in a chemistry that has to set around it, so past a certain loading you are diluting the cure rather than colouring it. The symptom is the same one a bad mix ratio produces: a surface that stays soft or tacky.

A workable rule is to treat anything over about six per cent as a figure to check against your resin’s data sheet before committing a whole batch to it, and to stay under ten in any case. If you need more opacity than that allows, two thinner coloured layers will get you there where one overloaded pour will not.

A Project Worked Through

A walnut river table. The channel runs 60 inches, the gap between the live edges averages 6 inches, and the pour is 1.5 inches deep. The resin is a deep-pour system, 2:1 by volume, rated to 2 inches a layer.

Channel volume  = 60 × 6 × 1.5      = 540 cubic inches
                = 540 ÷ 231         = 2.34 US gallons
Waste at 10%    = 2.34 × 1.10       = 2.57 gallons mixed

Split 2:1       resin    = 2.57 × 2/3 = 1.71 gallons
                hardener = 2.57 × 1/3 = 0.86 gallons

Depth check     1.5 in ≤ 2 in limit  → one pour

So: buy a three-gallon kit, mix it 2:1 by volume because that is the basis this kit states, and pour it in one go. Had the channel been 3 inches deep instead, the same tool would have called for two layers, and the sensible order would have been the same three gallons — the resin quantity does not change with layering, only the schedule does.

If that table then takes a 1/8-inch flood coat across its full 60 by 36 inch surface, that is 15 square feet, which at 12.83 square feet per gallon is another 1.17 gallons before waste. Two calculations, two orders, added together — not one calculation covering both.

Related Tools

For the volume of bulk material by the cubic yard rather than the litre, the gravel calculator and mulch calculator work the same geometry in the units landscaping suppliers sell in. For converting between litres, gallons and fluid ounces on their own, the unit conversion calculator handles it, and the percentage calculator is useful for working a pigment loading or a waste allowance back from a figure you already have.

Epoxy Questions People Ask