Self-Leveling Screed for 20 m2 - How Many Bags Do You Need?

How many bags does a 15 m2 bathroom floor actually need?

That depends on three numbers: the floor area, the layer thickness and the product consumption rate printed on the bag. A 15 m2 floor at 5 mm with a standard 1.6 kg/m2/mm compound needs 120 kg net - which rounds up to 6 bags of 25 kg with a 10% reserve. The calculator handles all of this in one step, including cost per square meter and a quick-reference table for common room sizes.

How to use the screed calculator - step by step

Choose input method - enter the area directly in m2, or calculate it from room length and width.
Layer thickness - desired screed thickness in mm. Typical range: 3-10 mm for self-leveling compounds. Check the product data sheet for min/max pour thickness.
Consumption rate - kg per m2 per mm of thickness. Most products are between 1.5 and 1.8. Default: 1.6. Always check the bag.
Bag size - 25 kg (55 lb) is standard in Europe, 50 lb (22.7 kg) is common in the US.
Reserve - 10% covers minor substrate irregularities. Use 15-20% for old or patched concrete with visible dips.
Read the results - bag count, total weight, net vs. reserve breakdown, surplus from rounding, and cost per m2.

Self-leveling compound types - an atlas

Not all floor levelers are the same. The product type determines the consumption rate, maximum thickness and drying time.

Cement-based (standard)

Consumption: 1.5-1.8 kg/m2/mm. Max thickness: 10-30 mm. Drying: 24-48 hours. The most common type for bathrooms, kitchens and living rooms under tile or laminate.

Gypsum-based (anhydrite)

Consumption: 1.8-2.2 kg/m2/mm. Max thickness: 50-80 mm. Drying: 3-7 days. Lower shrinkage, good for underfloor heating. Not suitable for wet areas without waterproofing.

Rapid-set / fast-drying

Consumption: 1.5-1.7 kg/m2/mm. Max thickness: 5-15 mm. Drying: 2-4 hours. Walkable the same day. Costs 30-50% more than standard cement-based.

Fiber-reinforced

Consumption: 1.6-1.9 kg/m2/mm. Max thickness: 10-40 mm. Contains synthetic or glass fibers for crack resistance. Used over weak substrates or for thicker pours.

Bags needed by room size and thickness

Reference table at 1.6 kg/m2/mm consumption, 25 kg bags, 10% reserve. Your product may differ - always check the data sheet.

Room	Area (m2)	At 3 mm	At 5 mm	At 10 mm
Small bathroom	6	2 bags	3 bags	5 bags
Kitchen	14	4 bags	6 bags	10 bags
Bedroom	18	4 bags	7 bags	13 bags
Living room	25	6 bags	9 bags	18 bags
Entire apartment	65	14 bags	23 bags	46 bags

Practical examples

Example 1: Bathroom 15 m2, 5 mm layer, 1.6 kg/m2/mm, 10% reserve, 25 kg bags
Result: 6 bags (120 kg net, 132 kg with reserve, 150 kg ordered)

Example 2: Living room 30 m2, 8 mm layer, 1.6 kg/m2/mm, 10% reserve
Result: 17 bags (384 kg net, 422.4 kg with reserve)

Example 3: Hallway 4 x 1.5 m = 6 m2, 3 mm layer, 1.5 kg/m2/mm, no reserve
Result: 2 bags (27 kg net, 50 kg ordered - 23 kg surplus from rounding)

Example 4: Entire apartment 65 m2, 5 mm layer, 1.6 kg/m2/mm, 15% reserve, $18/bag
Result: 24 bags, cost $432 ($6.65/m2)

Example 5: Garage 40 m2, 10 mm layer, 1.8 kg/m2/mm (fiber-reinforced), 20% reserve
Result: 35 bags (720 kg net, 864 kg with reserve)

FAQ - Frequently asked questions

What consumption rate should I use?

Check the product data sheet printed on the bag or the manufacturer website. Most standard cement-based self-leveling compounds fall between 1.5 and 1.8 kg/m2/mm. If no data is available, use 1.6 as a safe default.

How thick should my screed layer be?

For minor leveling (small dips, smoothing rough concrete): 3-5 mm. For moderate unevenness: 5-10 mm. For significant corrections or over underfloor heating pipes: 10-30 mm (use a thick-pour product). Most self-leveling compounds have a minimum pour thickness of 2-3 mm.

Do I need a primer before self-leveling?

Almost always yes. A primer seals the substrate and prevents it from absorbing water from the compound too fast (which causes cracking). Porous substrates (old concrete, plywood) need 1-2 coats. Non-porous substrates (tiles, epoxy) need a bonding primer. Check the product instructions.

Can I use self-leveling compound over underfloor heating?

Yes, but use a product rated for underfloor heating (check the data sheet). Pour thickness must cover the pipes by at least 5 mm above the top of the tube. Some products require the heating to be off for 48 hours after pouring.

Why do I need a reserve?

Self-leveling compound flows to the lowest point. If your substrate has dips, hollows or slopes that are not visible to the eye, the compound fills them and you run short on the opposite side. A 10% reserve handles typical minor irregularities. For old buildings or patched floors, use 15-20%.

How long does self-leveling screed take to dry?

Standard cement-based: 24-48 hours before walking, 3-7 days before tiling. Rapid-set products: 2-4 hours before walking, 24 hours before tiling. Gypsum-based: 24-48 hours before walking, 5-14 days before covering (moisture-sensitive). Always follow the product instructions.

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Self-leveling compound for 20 m2 - bags, weight and cost

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