Self-Levelling Compound Calculator
Estimate self-levelling compound volume, total weight, bags, mixing water and material cost for one or more floor areas.
- Calculation method: coverage per bag
- Extra allowance: 10%
- Bag weight: 20 kg
- Product rate: 4 m² per bag at 5 mm
- Mixing water: not entered
- Product thickness limits: not entered
Use this self-levelling compound calculator to estimate how much floor levelling compound you need for one or more rooms or floor areas. Enter the floor dimensions or total area, subtract any sections that will not be covered, choose the required thickness, then estimate compound volume, dry weight, whole bags, mixing water and optional material cost.
It is useful for DIY and trade flooring jobs such as smoothing uneven subfloors before laying tiles, vinyl, laminate, engineered wood or other floor finishes. For structural movement, serious cracking, damp substrates or floors outside the product specification, get advice from the manufacturer or a suitably experienced flooring professional.
PRO TIP: Measure the floor at several points before choosing a thickness. For an uneven floor, Advanced mode can divide the area into separate depth zones, which is usually more accurate than applying the deepest measurement across the whole room.
How to Use this Self-Levelling Compound Calculator
Choose Metric or Imperial units. Metric uses metres, square metres, millimetres, kilograms and litres. Imperial uses feet, square feet, inches, pounds and imperial gallons.
Select Standard or Advanced mode. Standard mode uses one average thickness for each floor area. Advanced mode can use separate depth zones and optional minimum and maximum product thickness limits.
Enter the floor area. Use Length × Width for a rectangular room, or select the direct area option if you already know the total floor area.
Enter any excluded area. Use this for a section that will not receive a compound. The excluded area must be smaller than the gross floor area.
Add more floor areas where required. The calculator can combine several rooms or floor sections in one estimate.
Enter the compound thickness. In Standard mode, use the average depth for each floor area. In Advanced mode, you can divide the net floor area into zones with different depths.
Choose how the product is specified. Select Coverage per bag or Consumption rate to match the figures printed on the packaging or technical data sheet.
Enter the bag weight and product figures. The default coverage method uses a 20 kg bag covering 4 m² at a 5 mm reference thickness. The default consumption method uses 1.6 kg/m²/mm.
Choose an extra allowance. The default is 10%, with options for none, 5%, 10% or 15%.
Add optional pricing and mixing water. Enter the cost per bag and water per bag to calculate an estimated total cost and water requirement.
Select Calculate Compound to view the combined results and floor-by-floor breakdown.
Results Explanation
The calculator shows the whole bags to buy, the exact bag requirement before rounding, total floor area, compound volume, dry material weight, allowance, final material weight and optional mixing water and cost.
Gross Area is the total measured area before exclusions. The excluded area is the part that will not receive the compound. Net Area is the area used in the material calculation.
Compound Volume is the space filled by the levelling compound. In metric mode, it is shown in cubic metres and litres. In imperial mode, it is shown in cubic feet and imperial gallons.
Net Material Weight is the estimated dry compound before the extra allowance. Allowance Weight is the additional material created by the selected percentage. Final Material Weight is the total after allowance.
Exact Bags is the mathematical bag requirement after allowance. Whole bags are rounded up, because self-levelling compound is normally purchased in complete bags.
The estimated cost is based on whole bags multiplied by the cost per bag. Mixing Water is based on whole bags multiplied by the water entered per bag.
In Advanced mode, the results can also show depth-zone breakdowns and warnings where an entered thickness is below the product minimum or above its maximum.
How the Maths Works
For a rectangular floor, the calculator uses:
length × width
For a directly entered floor area, it uses the area provided.
It then subtracts any excluded area:
gross area − excluded area = net area
For one average thickness, volume is calculated from:
net area × thickness
In metric units:
area in m² × thickness in mm ÷ 1,000 = volume in m³
For depth zones, it calculates each zone separately, then adds the results:
(zone area 1 × zone depth 1) + (zone area 2 × zone depth 2) + …
When the product uses a consumption rate, the material weight is:
area in m² × depth in mm × consumption rate in kg/m²/mm
When the product uses coverage per bag, the stated coverage is adjusted for the required thickness:
exact bags before allowance = area × required thickness ÷ (coverage per bag × reference thickness)
Material weight is then:
exact bags before allowance × bag weight
The calculator adds the selected allowance:
net material weight × (1 + allowance % ÷ 100)
Bags required are calculated by dividing the final weight by the bag weight, then rounding up:
final material weight ÷ bag weight
Cost and water are calculated from:
whole bags × cost per bag
and:
whole bags × water per bag
Common Mistakes to Avoid
Do not use the deepest point as the average thickness across the whole room. Take several measurements or use depth zones.
Do not forget to subtract areas that genuinely will not receive compound, but avoid subtracting movable furniture or sections that still need a continuous floor finish.
Do not confuse coverage per bag with a consumption rate. Use the method and units stated on the same product packaging or technical sheet.
Do not use a coverage figure without its reference thickness. A bag covering 4 m² at 5 mm will cover less area at a greater depth.
Do not assume every self-levelling compound has the same bag weight, coverage, water requirement or depth limits.
Do not add extra water to improve flow beyond the manufacturer’s permitted amount. Too much water can reduce performance and affect drying.
Do not ignore primer, substrate preparation, movement, moisture or product compatibility.
Do not buy only the exact decimal bag result. Bags are sold whole, so use the rounded-up whole-bag figure.
Do not start a large pour without enough material, mixing capacity and labour to maintain the product’s working time and a continuous wet edge.
faqs
How thick should self-levelling compound be?
Use the thickness needed to correct the floor while staying within the product’s stated minimum and maximum application depths. Some compounds are intended for thin smoothing layers, while others can be applied more deeply.
How much extra self-levelling compound should I allow?
The calculator offers no allowance, 5%, 10% or 15%, with 10% selected by default. A higher allowance may be sensible for rough, porous or very uneven floors, but accurate measurements remain important.
Do I need to prime before using self-levelling compound?
Many products require a compatible primer, particularly on absorbent or difficult substrates. Follow the manufacturer’s instructions for preparation, priming, drying times and substrate suitability.
Can I use self-levelling compound over timber?
Only use a product approved for the specific timber or boarded substrate. Movement and deflection must be controlled, and the system may require reinforcement, primer or a particular minimum thickness.
How do depth zones work?
Advanced mode lets you divide one floor area into zones with different depths. The zone areas must add up to the net floor area. The calculator works out each zone separately and combines the material requirements.
What is the difference between coverage per bag and consumption rate?
Coverage per bag states how much area one bag covers at a specified thickness. A consumption rate states the dry material needed per square metre for each millimetre of depth. Choose the option that matches the product data.
Does the calculator include mixing water?
Yes. Enter the manufacturer’s water quantity per bag and the calculator multiplies it by the whole-bag count. Mix each batch within the permitted water range rather than treating the total as one batch.
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Disclaimer
This calculator is for estimating self-levelling compound volume, dry material weight, bag quantities, mixing water and material cost only. It does not confirm that a product or floor build-up is suitable for a particular project.
Always check the current product packaging and technical data sheet for coverage, consumption, water dosage, primer requirements, substrate suitability, working time, curing time, minimum thickness and maximum thickness.
Check the floor for moisture, cracking, contamination, movement and weak or loose material before starting. Seal gaps where fluid compound could escape and protect adjoining surfaces.
For structural movement, serious substrate defects, damp floors, underfloor heating concerns or work outside the product specification, get advice from the manufacturer or a suitably qualified flooring professional.