How to use this calculator
- 1Measure the floor, or enter the area directly.
- 2Find the average depth you need to fill: check the floor with a long straight edge or a laser level in several places.
- 3Choose the type of product. Its typical consumption fills in; replace it with the figure on your bag if it differs.
- 4Enter the bag weight to see how many bags to buy — or, if you mix sand and cement yourself, choose the mix and your cement bag size to get cement bags and sand.
The formula
- 01Material (kg) = area (m²) × average depth (mm) × consumption (kg per m² per mm) × (1 + extra %)
- 02Bags = material ÷ bag weight, rounded up
- 03Volume = area × depth × (1 + extra %)
- 04Area per bag = bag weight ÷ (consumption × depth)
- 05Mixed on site: dry volume = area × depth × (1 + extra %) × 1.33; cement = dry volume × 1 ÷ (1 + sand parts)
- 06Cement bags = cement volume × 1,440 kg/m³ ÷ bag weight, rounded up; sand = dry volume × sand parts ÷ all parts
Levelling products are sold by weight, but you fill a volume. Manufacturers therefore give a consumption figure: how many kilograms you need for one square metre at one millimetre thick. Self-levelling compounds use about 1.4–1.7 kg per m² per mm, while sand and cement screeds and flowing screeds use about 1.8–2.0 kg. We use the higher figure of each range so you do not run short.
The figure in kg per m² per mm is the same number as the density of the set material in kg per litre or tonnes per m³ — one litre spread over one square metre is exactly one millimetre deep.
Floors are rarely flat, so the average depth matters more than the deepest point. The extra allowance covers low spots, compound that flows into gaps and what is left in the bucket.
When you mix sand and cement yourself, the parts are measured by volume. For 1 m³ of 1 : 4 screed that is about 383 kg of cement (7.7 bags of 50 kg) and 1.06 m³ of sand. A 50 mm screed on 12 m² with 10 % extra needs 253 kg of cement — buy 6 bags of 50 kg — and 0.7 m³ (25 ft³) of sand.
Worked example
A 4 m × 3 m floor levelled to an average of 5 mm with self-levelling compound at 1.7 kg/m² per mm needs 102 kg of powder.
With 10% extra that is 112.2 kg, or 5 bags of 25 kg. Each bag covers about 2.94 m² at this depth.
Tips before you buy
- Mix whole bags with the exact amount of water on the bag — extra water weakens the compound and makes it crack.
- Self-levelling compound sets fast. Have everything ready, work in bays with a helper mixing, and pour each batch against the edge of the last.
- Seal gaps at the walls, pipes and floorboards with sealant or foam strip first, or the compound will run away underneath.
- Check drying times before planning the floor covering: a thin compound may take tiles within hours, but a sand and cement screed needs weeks to dry.
Frequently asked questions
How much self-levelling compound do I need per m²?
About 1.5–1.7 kg for every square metre at 1 mm deep. At 3 mm that is roughly 5 kg per m², so a 25 kg bag covers about 5 m². Always check the figure on your product.
How many square feet does a 50 lb bag of floor leveler cover?
It depends on the depth. One manufacturer's chart, for example, gives 46–48 ft² per 50 lb bag at 1/8 in and 23–24 ft² at 1/4 in. Twice the depth covers half the area, so check the chart on your bag.
How thick can self-levelling compound be?
It depends on the product. Many standard compounds are made for about 1–10 mm in one layer; others go to 30 mm (over 1 in) or more. Thicker layers usually need a deep-fill compound or a screed.
What is the difference between screed and self-levelling compound?
A screed is a thicker layer (usually 25 mm or more) of sand and cement or a flowing calcium sulfate mix that forms the floor base. Self-levelling compound is a thin, fluid layer that smooths and levels a floor just before the floor covering goes down.
Do I need to prime the floor first?
Almost always. Primer controls how fast the floor absorbs water from the compound and improves the bond. Use the primer the compound's maker recommends for your type of floor.
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Sources
- Mapei Ultraplan: 1.6 kg/m² per mm, 1–10 mm
- CUSTOM LevelQuik RS data sheet (TDS-108): 46–48 ft² per 50 lb bag at 1/8 in
- Mapei Topcem Pronto screed: 18–20 kg/m² per cm
- Screed thickness guidance (BS 8204-1) — The Concrete Society
- Sand and cement per m³ of screed (1:3, 1:4, 1:5; dry volume factor 1.33; cement 1,440 kg/m³) — Civil Sir
Formulas last reviewed: September 30, 2026 ·How we check our formulas