Work out how much self-leveling compound you need for a floor. Enter the area, average layer thickness and your product's consumption or coverage to estimate whole bags and purchase cost.
How much self-leveling compound do I need?
You need the floor area, the average thickness of the new layer and the coverage of the product you plan to buy. Bag weight alone is not enough. Two products in equally heavy bags can have different coverage.
This self-leveling compound calculator, also called a floor levelling compound calculator, estimates material for one or more floor zones. It adds their requirements, includes your chosen reserve and rounds up once to whole bags or complete kits. The cost uses the number you still need to buy after usable stock.
Measure area and layer thickness
For a rectangle, multiply length by width. Split an L-shaped floor into rectangles that do not overlap, or enter a known measured area. Deduct fixed areas only when you will not apply compound there. Keep doorways, recesses and other areas that will receive the same layer in the measurement.
Thickness means the depth of material needed above the existing surface to reach the planned finished level of the compound. It is not the thickness of the final floor covering. Measure the floor against that target level at enough points to understand the high and low areas. A laser level or another suitable surveying method can help establish those differences.
Use an average that represents the area of each zone. Do not simply average the highest and lowest readings across an irregular floor. A deep hollow covering a small corner should not be treated as though it covers the whole room. More, smaller measured zones give a better estimate when depth varies.
The formulas behind the result
One square metre covered to a depth of one millimetre has a geometric layer volume of one litre. For each zone:
Layer volume in litres = net area in m² × average thickness in mm.
Add all zone volumes, then multiply by 1 + reserve percentage ÷ 100. If the technical sheet gives dry powder consumption:
Dry powder in kg = layer volume in litres × consumption in kg/m²/mm.
Whole bags = powder needed with reserve ÷ dry powder weight per bag, rounded up.
If the sheet gives coverage per bag or kit instead:
Layer volume per bag = stated coverage in m² × stated reference thickness in mm.
Whole bags or kits = total layer volume with reserve ÷ layer volume per bag, rounded up.
The calculator converts feet, inches and square feet before applying these formulas. Litres describe the space occupied by the layer. They are not litres of mixing water, loose powder or a mixing-bucket instruction. The powder consumption figure is not a general wet density.
Example: a 20 m² floor with uneven depth
Suppose one 12 m² zone needs an average 3 mm layer and another 8 m² zone needs 8 mm. Their volumes are 36 L and 64 L, giving 100 L in total. The area-weighted average thickness is 100 ÷ 20 = 5 mm.
For an illustrative product that uses 1.6 kg/m²/mm, the floor needs 160 kg of dry powder before reserve. Adding 10% gives 176 kg. With 25 kg bags, divide 176 by 25 to get 7.04 bags, then round up to 8 bags. Those bags contain 200 kg, leaving a 24 kg allowance above the estimate including reserve.
If you already have 2 usable bags, buy 6 more. At an entered price of €22 per bag, the additional purchase cost is €132. These are example values for learning the calculation. Replace the consumption, pack weight and price with the data for your selected product. The Try an example button loads this calculation.
Read bag coverage together with its thickness
A label saying a bag covers 7 m² does not mean it will cover 7 m² at every depth. For example, ARDEX K 11 lists approximate coverage of 7 m² at 2 mm for a 22 kg bag. That is about 14 L of layer volume per bag. A 100 L floor plus 10% reserve would therefore require 110 ÷ 14, rounded up to 8 bags, using that published coverage.
That example explains coverage, not product selection. Check the current technical sheet for your market and pack. The manufacturer's technical sheet also sets product-specific layer, substrate, priming and mixing requirements. If a system uses a separate liquid component, calculate and price the complete matching kit.
Choose reserve and check the product limits
A reserve can allow for measured uncertainty, surface texture and handling losses. The calculator starts at 10% so you can see and change it. There is no single reserve that suits every floor. Improve uncertain measurements first, then choose an allowance that fits the project and the product guidance.
Check actual minimum and maximum depths separately from the average. A zone averaging 5 mm may still have places thinner or deeper than your chosen product allows. This calculator does not approve those depths or decide whether the substrate is suitable.
Product guidance also controls surface preparation, primer, moisture conditions, mixing liquid, working time and when the floor covering can be installed. Do not add extra water to stretch coverage. Where a product permits aggregate extension or another special build-up, use the manufacturer's stated yield for that exact system rather than guessing an adjusted rate.
Common questions
Can I use this for screed or a structural concrete slab?
Use it for estimating a chosen floor levelling compound from its published consumption or coverage. It does not design a structural slab, a screed system, reinforcement or an underfloor-heating build-up. Those require the appropriate system specification.
Why not round up the bags for every room?
Rounding each room first can increase the total unnecessarily. This calculator adds material requirements for the same product and pack size, then rounds once. If work is split into separate days or packs cannot be shared, plan those stages separately and follow storage and mixing instructions.
Can I count an opened bag as stock?
The stock field accepts complete usable bags or kits only. Check condition, storage and shelf life. Do not count a partly used kit as complete or assume that an opened product remains usable. To avoid underbuying, leave uncertain stock out of this estimate.
Does the price include primer and the final floor covering?
No. It calculates the additional bags or complete kits at the price you enter. Add primer, repairs, tools, labour, delivery and other costs separately. Plan the finish with our flooring calculator or tile calculator, and use the baseboard calculator for the edges.
