Epoxy is bought in two containers and used as one material, which makes estimating it slightly odd. You need a total volume set by geometry — area times depth — and then a split into resin and hardener set by chemistry. The epoxy resin calculator above does both: it converts your pour into gallons or litres of mixed material, applies a waste factor, and divides the result at the exact ratio your product specifies, in whichever basis that ratio is quoted.
Arb Digital publishes it as part of a free construction and finishing library. It shares its geometry with our square footage calculator and its coverage logic with the paint calculator, but epoxy differs from paint in a way that matters: paint is applied at a rate, epoxy is poured to a depth, and a small error in depth changes the order by a lot more than most people expect.
What This Epoxy Resin Calculator Does
It computes the volume of the space you are filling, converts it into the units epoxy is actually sold in, and splits it. The split respects whether your product's ratio is quoted by volume or by weight, which are not interchangeable, and it uses the densities you supply to convert between the two so the weight figures are right either way.
It also multiplies by a number of coats, because most surface work is done in more than one pour — a thin seal coat that wets the substrate and blocks outgassing, then one or more flood coats to build depth. Each of those is a separate mix with its own pot life, and estimating them as a single deep pour is both a quantity error and, on many products, a safety one.
How to Use It
- Describe the pour. A rectangle from length and width, a circle from a diameter, or a straight area figure if you already have one.
- Enter the depth of one pour, and how many pours. Not the total depth in one go — your product's data sheet sets the maximum depth of a single lift.
- Enter your product's mix ratio and say which basis it is quoted in. This is the field people get wrong, and it is the one the cure depends on.
- Enter both densities from the data sheet if you want reliable weight figures. Resin and hardener are rarely the same density.
- Set a waste factor. Ten percent is a sane default: epoxy clings to mixing vessels and stir sticks, and a batch you cannot pour is a batch you paid for.
The Formula / How It's Calculated
Volume = area × depth × coats, then ordered volume = volume × (1 + waste). In imperial the tool works in cubic inches and divides by 231 to get US gallons; in metric it works in cubic millimetres and divides by one million to get litres. The split is resin = total × A ÷ (A + B) and hardener = total × B ÷ (A + B), applied to volume if the ratio is quoted by volume and to weight if it is quoted by weight.
Take the default: a table top 60 in by 36 in, poured 0.25 in deep in one go. The area is 2,160 square inches and the volume is 540 cubic inches, which is 540 ÷ 231 = 2.34 US gallons. Add 10 percent waste and you are buying 2.57 gallons of mixed epoxy. At 2:1 by volume that is 1.71 gallons of resin and 0.86 gallons of hardener. Using the placeholder densities of 9.7 and 8.4 pounds per gallon, the mixed weight comes to about 23.8 pounds.
A useful sanity check to carry in your head: one US gallon spread at one eighth of an inch covers 12.8 square feet, and at a quarter inch it covers 6.4 square feet. In metric, one litre at 3 mm covers about a third of a square metre. If a supplier's coverage claim is far from those figures, they are quoting a different film thickness than you are assuming.
Ratio by Volume and Ratio by Weight Are Different Numbers
This is the single most consequential detail on the page. A system quoted as 2:1 by volume is not 2:1 by weight, because resin is typically denser than hardener. Using the placeholder densities above, 2 volumes of resin at 9.7 lb per gallon weigh 19.4 units while 1 volume of hardener at 8.4 weighs 8.4, so the same mix is about 2.31:1 by weight. Measure that system 2:1 on a scale and you have added roughly 14 percent too much hardener.
Epoxy is not a catalysed system where more hardener means a faster cure. The two components react in a fixed stoichiometric proportion, and the excess of whichever one you over-added simply does not react. That leaves unreacted material in the cured film, which shows up as permanent tackiness, soft patches, a cloudy finish, or a surface that never reaches full hardness no matter how long you wait. There is no fix once it has cured; the piece gets stripped and redone. The rule is straightforward: read whether the ratio is by volume or by weight, then measure in that basis.
Exotherm: Why Depth Is Limited and Volume Is Not
The epoxy reaction gives off heat, and heat accelerates the reaction, which gives off more heat. In a thin film that heat escapes into the air and the substrate and nothing happens. In a deep pour, or in a full mixing cup left standing, it cannot escape — the temperature climbs, the pot life collapses, and a batch that should have stayed workable for twenty minutes can smoke, yellow, crack or set solid in the bucket in a fraction of that time.
Three practical consequences follow. First, maximum single-pour depth is a hard product property; deeper work is done in lifts, waiting between them. Second, a large batch cures faster than a small one at the same temperature, so scaling up a mix you have used before shortens your working time. Third, pouring the mix out of the cup into a wide shallow tray immediately after mixing buys you working time, because the same volume spread thin sheds heat far better. Deep-pour products exist specifically for casting work and are formulated with slower chemistry, which is why they are not interchangeable with coating grades.
Substrates, Seal Coats and Where the Extra Volume Goes
Porous substrates absorb epoxy and out-gas air into it. A raw timber slab, an unsealed concrete floor and an open end-grain surface all draw material into their pores, and the air trapped in those pores expands as the surface warms, pushing bubbles up through a curing film. That is why a thin seal coat goes on first: it fills and blocks the pores, and it cures enough to stop the flood coat lifting bubbles.
For estimating, this means a first pour over an absorbent substrate covers less than the geometry suggests. On rough or open material, add the absorbed volume through the waste factor rather than assuming the seal coat is free. Edges are the other quiet consumer: epoxy runs off a table top and forms a curtain down the sides, all of which is material you bought and most of which ends up on the plastic sheeting underneath. Taping a dam around the perimeter converts most of that loss back into pour.
Handling the Material Safely
Uncured epoxy components are not benign. Occupational health authorities associate epoxy and resin systems with skin sensitisation, dermatitis, occupational asthma and hypersensitivity pneumonitis, and the US National Institute for Occupational Safety and Health also flags reproductive health concerns for some constituents — its guidance on epoxies and resins is the reference worth reading before a first project. The point most often missed is glove selection: thick nitrile or butyl rubber is appropriate, while latex and cotton absorb and hold these chemicals against the skin, making them worse than no glove at all.
Sensitisation is the risk that changes behaviour. It is cumulative and it is permanent — once someone reacts to an epoxy component, they generally react to it for life, and casual contact that caused no trouble for years is what produced it. Ventilate, keep the material off skin, and follow the safety data sheet for the specific product. Cured epoxy is a different proposition from uncured, though sanding it produces dust that should not be inhaled. Test methods and material specifications for these systems are published by bodies such as ASTM International, and unit and quantity conventions follow the NIST guide to the SI.
Arb Digital builds free, fast, search-friendly tools that bring makers, fabricators and suppliers steady organic traffic. Browse the library or tell us what your customers keep asking you to work out.
Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Measuring a volume ratio on a scale — different densities mean the two bases give different numbers, and the excess component never reacts.
- Pouring the full depth in one lift — trapped reaction heat can crack, yellow or flash-cure a deep pour, and the safe depth is a product property.
- Leaving the mixed batch in the cup — a tall mass of epoxy heats itself and loses most of its working time. Pour it out immediately.
- Ignoring run-off at the edges — an unbounded top loses real volume down its sides, and a taped dam recovers most of it.
- Skipping the seal coat on porous work — absorbed epoxy and out-gassed air both come out of the flood coat as bubbles.
Related Free Tools From Arb Digital
Measure the surface with the square footage calculator or the circle calculator for round tops, convert quantities with the volume converter, price the result with the cost per square foot calculator, estimate the timber with the board foot calculator, and handle coatings that go on by rate rather than depth with the paint calculator. Everything else is on the free online tools hub.
Frequently Asked Questions
Multiply the area by the pour depth. A 60 by 36 inch top at a quarter inch deep is 2,160 square inches times 0.25, or 540 cubic inches, which is 2.34 US gallons. Add a waste factor of around ten percent for material left in cups and lost over the edges.
One US gallon spread at one eighth of an inch covers 12.8 square feet, and at a quarter inch it covers 6.4 square feet. Coverage claims that differ sharply from those figures are quoting a different film thickness, so always check what depth a supplier is assuming.
It depends entirely on the product, and the two are not the same number. Because resin is usually denser than hardener, a system that is 2:1 by volume can be around 2.3:1 by weight. Read the data sheet, then measure in whichever basis it states.
Epoxy is not catalysed, so extra hardener does not speed the cure. The components react in a fixed proportion and the excess simply stays unreacted in the film, which shows up as permanent tackiness, soft spots or a surface that never fully hardens. Cured mis-ratioed epoxy cannot be rescued.
The reaction releases heat, and in a deep pour that heat cannot escape, so it accelerates the reaction further. The result can be cracking, yellowing or a batch that sets in minutes. Maximum single-lift depth is specific to the product, and deep-pour formulations use slower chemistry for exactly this reason.
On porous substrates such as raw timber or open concrete, yes. The substrate absorbs material and releases trapped air into the curing film as bubbles. A thin seal coat fills the pores first, and its volume should be included in your estimate rather than assumed away.
Uncured components are skin sensitisers and respiratory irritants, and sensitisation is cumulative and generally permanent. Occupational health guidance points to thick nitrile or butyl rubber gloves, because latex and cotton absorb these chemicals and hold them against the skin. Follow the safety data sheet for your specific product.
This tool estimates material quantities only. Mix ratios, maximum pour depths, pot life, cure schedules and handling precautions are properties of the specific product you have bought and must be taken from its technical data sheet and safety data sheet. Uncured epoxy components carry real health risks, and this page is not a substitute for the manufacturer's instructions or for occupational health guidance.
