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ARDEX K 15 Coverage Calculator: How Many Bags of Self-Leveler?

Enter your floor area and the average pour thickness to see how many 55 lb (25 kg) bags of ARDEX K 15 to buy. ARDEX rates one bag at 30 sq ft at 1/4 inch; the calculator scales that to your thickness. The figures come from the ARDEX Americas technical data sheet updated 2026-04-02.

ARDEX K 15 coverage

Source: ARDEX Americas Technical Data Sheet: ARDEX K 15 Premium Self Leveling Underlayment, content updated 2026-04-02, read 2026-10-16.

How the calculation works

bags = area × (1 + waste ÷ 100) × thickness ÷ (coverage at reference thickness × reference thickness), rounded up

Self-leveler volume scales with thickness: twice as thick needs twice as many bags. Low spots in the floor add to the real average thickness, so measure the deepest point and the average before you pour.

Worked example

A 200 sq ft floor poured 0.25 in thick with 10% extra: 220 sq ft to cover. One bag covers 30 sq ft at 0.25 in, so at 0.25 in it covers 30 × 0.25 ÷ 0.25 = 30 sq ft. 220 ÷ 30 = 7.33 bags, so buy 8 (440 lb).

ARDEX K 15 key specs

What ARDEX K 15 is for

ARDEX K 15 is a cement-based, polymer-modified self-leveling underlayment made in the USA by ARDEX Americas. You mix it with water only, pour it, and it flows out into a flat, smooth surface that can take tile, stone, carpet, vinyl and most other floor coverings. ARDEX describes it as the original and most specified self-leveler in North America, and it is aimed at professional installers: the data sheet notes that ARDEX does not sell it through home improvement centers. It is an underlayment, not a finished floor, so it always needs a floor covering on top.

The data sheet lists these substrates: structurally sound concrete, absorbent terrazzo on concrete, non-aluminum metal (after talking to ARDEX technical service), ARDEX MC RAPID and ARDEX VB 100 moisture control systems, and several non-porous surfaces on concrete, including ceramic, quarry and porcelain tile, epoxy flooring and epoxy terrazzo, and well-bonded, non-water-soluble adhesive residue. It is for interior, dry areas only, on, above or below grade.

Why thickness matters more than area

With thinset, the trowel notch decides how much mortar goes on the floor. With a self-leveler, the depth of the pour decides everything. One 55 lb bag of K 15 makes roughly the same volume of material every time, about 30 sq ft × 1/4 inch, or 0.625 cubic feet. Pour it twice as thick and it covers half the area. That is why this calculator asks for thickness and why getting that number right matters more than measuring the room to the last inch.

The problem is that floors are rarely flat to start with. If you need 1/8 inch over the high spots but the floor has a dip of 1/2 inch in one corner, the average thickness can be well above what you planned. ARDEX gives an average minimum of 1/4 inch and says that 1/8 inch over the highest point typically produces at least that average. A practical way to estimate the average:

• Stretch a straightedge or a string line across the floor and measure the gap at regular intervals, for example every 2 feet.
• Add the depth you want over the highest point to each reading, then average all the numbers.
• If one area is much deeper than the rest, run the calculator separately for that zone and add the results.

The waste allowance in the calculator covers material left in the mixing bucket, the pump hose and spills. Ten percent is a reasonable starting point for hand mixing two bags at a time; a pumped job with long hose runs may need more.

Thickness limits

K 15 can be poured up to 1 1/2 inches (4 cm) thick neat in most applications. For deeper fills, up to 5 inches (12.7 cm), ARDEX allows you to extend it with washed, well-graded pea gravel no larger than one third of the pour depth and no smaller than 1/8 inch, added at 1 part gravel by volume after the powder and water are mixed. Sand must not be used. Aggregate makes the mix stiffer, so ARDEX notes you may need a neat top coat, poured after the first layer dries and is primed with ARDEX P 51. When you extend with gravel, the gravel takes up part of the volume, so you need fewer bags than the calculator shows for that depth; this calculator assumes a neat pour.

There is one important exception: over substrates primed with ARDEX P 82 Ultra Prime, ARDEX P 4 or the ARDEX VB 100 moisture control system, the maximum thickness is only 1/4 inch (6 mm). If your floor needs more than that over one of those primers, check the data sheet and ARDEX technical service before planning the pour. The calculator warns you when you enter a thickness outside the 1/4 to 1 1/2 inch range for a neat pour.

Priming and preparation in brief

The data sheet ties the primer to the substrate. Standard absorbent concrete gets ARDEX P 51 diluted 1:1 with water, applied with a soft push broom; very absorbent concrete gets a "double prime" with a 1:3 first coat. Non-absorbent concrete and other non-porous surfaces get ARDEX P 82, and ARDEX P 4 is a pre-mixed option for many substrates. The primer has to be dry before you pour: for P 51, ARDEX describes a simple test of rubbing water on the primed surface and checking that it stays clear.

Concrete should be mechanically cleaned where needed. ARDEX says not to use acid etching, adhesive removers, solvents or sweeping compounds, which act as bond breakers. Moving joints and moving cracks must be carried up through the underlayment and the floor covering, not poured over. ARDEX also asks you to test concrete relative humidity to ASTM F2170 and to use a moisture control system if the reading exceeds the limits of the floor covering or adhesive, or 99%.

Mixing and timing

Each bag takes 7 quarts (6.6 L) of clean water. ARDEX recommends mixing two bags at a time with a 1/2 inch heavy-duty drill and paddle, then spreading with a gauge spreader and smoothing or spike-rolling straight away. The material flows for about 10 minutes at 70°F (21°C), so have the next batch ready. Substrate and air must stay at 50°F (10°C) or above during installation and cure, and radiant floor heat should be off from 48 hours before until 48 hours after the pour. Moisture-insensitive tile can follow after about 6 hours; other floor coverings after 16 hours.

FAQ

How much does a bag of ARDEX K 15 cover?

ARDEX's data sheet gives 30 sq ft (2.8 m²) per 55 lb (25 kg) bag at 1/4 inch (6 mm). Coverage scales with thickness, so the same bag covers about 15 sq ft at 1/2 inch, 7.5 sq ft at 1 inch and 5 sq ft at 1 1/2 inches. ARDEX notes that real coverage depends on the surface profile, density and porosity of the floor.

What thickness should I enter?

Enter the average thickness over the whole area, not the thickness at the highest point. ARDEX lists an average minimum thickness of 1/4 inch and says that 1/8 inch over the highest point of the floor typically gives at least that average. If you have deep low spots, measure them and work out an average, or split the floor into zones and run the calculator for each.

How much water goes in a bag of K 15?

7 US quarts (6.6 L) of clean water per 55 lb bag. ARDEX says to mix two bags at a time, pour the water in first, then add powder while mixing with a heavy-duty 1/2 inch drill at 650 rpm or more for about 2 to 3 minutes. Extra water weakens the compound; yellowish foam or sand settling out are signs of overwatering.

How thick can ARDEX K 15 be poured?

Up to 1 1/2 inches (4 cm) neat in most cases, and up to 5 inches (12.7 cm) when extended with washed pea gravel. Over substrates primed with ARDEX P 82, ARDEX P 4 or ARDEX VB 100, the maximum is 1/4 inch (6 mm). It can be tapered to meet existing elevations; for a true featheredge ARDEX points to ARDEX FEATHER FINISH instead.

When can I tile over ARDEX K 15?

At 70°F (21°C), it is walkable after 2 to 3 hours, moisture-insensitive tile such as ceramic, quarry and porcelain can go down after 6 hours, and all other floor coverings after 16 hours. Low temperatures and high humidity extend those times.

ARDEX and ARDEX K 15 are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.