Epoxy Resin Calculator UK · metric

Litres of resin for garage floor coatings and deep pours. Metric units and £ costs, updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

A thin-film garage coating uses about 0.35 litres per m² over two coats. A self-levelling pour is area × thickness (1 m² at 1 mm = 1 litre), plus 10% waste. Costs use a UK per-litre kit price.

The waste allowance

The calculator adds 10 per cent for mixing losses and edge run-off, which is a modest allowance and deliberately so. Two-part epoxy is not like emulsion: once resin and hardener are combined the clock starts, the pot life is fixed, and whatever is left in the bucket when it gels is refuse. You cannot decant half a kit and keep the rest for next weekend, so the practical unit of purchase is the pack rather than the litre. The larger risk on a floor is not running 10 per cent short on material. It is preparing the slab badly or coating it while it is still damp, in which case the coating fails whatever quantity you bought. Budget the contingency in time and preparation, not only in resin.

Why a litre of floor coating covers so much less than a litre of emulsion

This surprises people, and it should not, because it is arithmetic rather than mystery. Watco quote their Epoxy Resin Floor Paint at 30 square metres per 5 litre pack per coat, which is 6 square metres per litre, at a dry film thickness of 100 microns, applied in two coats. Compare that with a trade vinyl matt emulsion at up to 17 square metres per litre. The floor coating covers roughly a third as much ground from the same volume.

Coverage is the relationship between a volume of material and the thickness of the film that volume is spread into. A wall emulsion is built to leave a thin dry film and to stretch, because nothing walks on it. A floor coating is built to leave 100 microns per coat, twice over, and to survive tyres, dropped spanners and grit. Multiply the film thickness and the area a fixed volume covers falls by the same factor.

Note that British data sheets state film thickness in microns, not in mils. A hundred microns is a tenth of a millimetre. If you are reading American guidance that talks about mils and square feet per gallon, do not convert it — find the figure for the product you are actually buying, because solids content and recommended build vary between products far more than the unit conversion suggests. Two coats of the Watco product at 6 square metres per litre per coat works out at roughly a third of a litre per square metre for the finished floor, which is where this calculator's thin-film figure comes from.

The slab has to be ready, and in Britain that means two months rather than four weeks

New concrete needs to be old enough before it is coated, and the British figure is longer than the one usually quoted in American guidance. Watco specify that new concrete should be at least two months old before their epoxy floor paint goes on, and eight weeks before Resiflow, their self-levelling epoxy, with a dedicated new concrete primer offered if you cannot wait. The familiar 28 day figure is a strength milestone, not a dryness one, and a slab that has reached its design strength is still giving off a great deal of water.

The surface then has to be given a key. A smooth power-floated or trowel-finished slab is the classic failure case, because it looks like the ideal surface to coat, which is exactly the problem: a burnished surface is closed and offers almost nothing for the coating to grip. Adhesion here is mechanical. Watco specify degreasing with a proprietary cleaner and abrading any smooth glossy areas to provide a key, and their self-levelling system specifies an etch and clean stage before anything is poured.

Mechanical profiling with a diamond grinder or a shot blaster is more reliable than acid etching, mostly because it is harder to do inadequately. Acid etching works when it is done thoroughly and rinsed properly, and it fails quietly when it is not. Either way the test is the same: a properly profiled slab feels like medium grit abrasive paper and takes a drop of water into itself rather than beading it.

Moisture, and what the British test actually is

The most common cause of resin floor failure is moisture vapour moving up through the slab, and it is also the step most routinely skipped. Concrete on the ground sits above damp earth, and water vapour travels up through it continuously. While the floor is uncoated that vapour simply leaves. Put a largely impermeable film over the top and it arrives at a barrier instead, builds pressure under the coating and lifts it. The result is blistering and delamination, sometimes months after the job looked finished.

The British test is the insulated hygrometer test, which the Concrete Society describe as the preferred method, following the procedure in BS 8203. The limit generally quoted is a surface relative humidity of 75 per cent or less. There is an in-situ probe variant, on which Contract Flooring Association guidance gives 24 hours as sufficient to reach equilibrium and an upper limit of 85 per cent, the difference being that the probe measures conditions inside the slab while the hygrometer box measures what is leaving the surface. Resistance-type moisture meters are explicitly not recommended.

Two honest caveats. First, BS 8203:2017 is the code of practice for installing resilient floor coverings and BS 5325:2021 is the equivalent for textile floor coverings — they are floorcovering codes, and the hygrometer procedure in them is what British flooring and resin contractors have adopted for coatings, but neither is a standard written for epoxy floor paint. Second, drying takes far longer than people expect. The Concrete Society note that around a quarter to a third of the original water in a slab has to evaporate, perhaps 6 to 9 litres per square metre for a 150 millimetre slab, and that it takes many months to reach 75 per cent at the surface. If the slab fails the test, the answer is a liquid damp proof membrane or a moisture vapour suppressant, not a thicker coat of epoxy.

Thin film against a self-levelling pour, and conditions on the day

These are two different products doing two different jobs and the arithmetic is not the same. A thin-film garage coating is bought by coverage: 6 square metres per litre per coat, two coats, so about a third of a litre per square metre. A self-levelling pour is bought by volume, because you are specifying a thickness in millimetres rather than a film in microns. One square metre at one millimetre is one litre, so a 3 millimetre pour over 18 square metres is 54 litres before waste.

The complication is that self-levelling resins are usually sold by weight rather than by volume, so the identity needs a density conversion before it becomes a shopping list. Watco Resiflow comes in 20 kilogram packs quoted at 5 to 10 square metres per pack, applied at around 1.5 millimetres. That range spans a factor of two on the same pack, entirely because of applied thickness, which is a fair warning against planning a resin screed from a headline coverage figure. Work from the pack's own stated coverage at your intended thickness.

Conditions on the day catch people out in British garages more than anywhere else. Watco specify a minimum floor temperature of 10 degrees Celsius for both products and a minimum application temperature of 15 degrees for the floor paint, and UK trade guidance is firm that the temperature that matters is the floor's rather than the air's, measured with an infrared thermometer at the cold spots near doorways and vents. Humidity above about 85 per cent rules out application as well. A widely used dew point margin is 3 degrees Celsius between substrate and dew point, but it comes from ISO 12944-7, which is written for protecting steel structures rather than concrete floors, so treat it as a working margin rather than a figure specific to your slab. An unheated slab holds overnight cold well into a mild afternoon, which is exactly when condensation forms on it.

Floor coating figures and prerequisites

Coverage and conditions below are as published by Watco for two specific British products, one thin-film and one self-levelling. The preparation and moisture items are conditions the coating depends on rather than optional refinements.

Coverage, film thickness, pack sizes, minimum temperatures and concrete age from the Watco UK product data for Epoxy Resin Floor Paint (30 m² per 5 L per coat, 100 microns dry film, two coats, 2.5 L and 5 L packs, new concrete at least two months old, cure 24 hours at 20°C) and Watco Resiflow (5 to 10 m² per 20 kg, about 1.5 mm, eight weeks concrete cure, 10°C minimum). Moisture testing from the Concrete Society's guidance on moisture in new concrete floors, which names the insulated hygrometer test procedure in BS 8203 as the preferred test, gives 75 per cent surface RH as the limit flooring suppliers state, notes that 6 to 9 litres per m² must evaporate from a 150 mm slab and that resistance meters are not recommended; and from the Contract Flooring Association guidance note on in-situ probe measurement (24 hours to equilibrium, 85 per cent upper limit within the slab). BS 8203:2017 is the code of practice for installation of resilient floor coverings and BS 5325:2021 the equivalent for textile floor coverings; neither is written for resin coatings. The 3°C dew point margin is from ISO 12944-7, a standard for the protection of steel structures. The 1 litre per m² per mm figure for self-levelling pours is arithmetic, not a manufacturer's published rate.

What goes wrong on garage floor coatings

Coating a slab that is too young. Watco specify at least two months for their epoxy floor paint and eight weeks before Resiflow. The 28 day figure people remember is when concrete reaches its design strength, which has nothing to do with whether it has finished releasing water.

Skipping the moisture test. Vapour rising through a slab is the most common cause of resin floor failure and the test that catches it is the one most often left out. The British method is the insulated hygrometer test to BS 8203, with a limit of 75 per cent surface relative humidity. Resistance-type meters are not recommended for this.

Converting American figures. Mils and square feet per gallon belong to different products with different solids contents. A UK data sheet gives square metres per litre and microns, and those are the figures to buy from. Watco's 6 m² per litre at 100 microns is not the same product as anything quoted in gallons.

Coating a power-floated slab as it is. A burnished surface gives the coating nothing mechanical to grip. Degreasing, etching or grinding is what creates adhesion, and without it the film delaminates, usually after it has been in service long enough to feel like a success.

Going by the air temperature. Watco specify a floor minimum of 10°C and application at 15°C or above for the floor paint. Concrete holds overnight cold well into a mild afternoon, and the cold spots by doorways and vents are where condensation forms first. Measure the slab with an infrared thermometer.

Frequently asked questions