Self-Leveling Underlayment Calculator
How many bags of self-leveling underlayment a floor takes at an even depth or across a sloping floor, from the yield printed on the bag.
Result
Enter floor and area one bag covers to see the result.
https://calcgallery.com/flooring-tile/self-leveling-underlayment-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Self-Leveling Underlayment Calculator
- Enter the floor as one or more rectangles.
- Choose an even depth, or a sloping floor with its shallow and deep sides.
- Copy the yield from the bag, either the area it covers at a stated depth or the volume it makes.
- Read the bags to buy, and add an allowance under More options if the floor is porous or uneven.
How it is calculated
average depth = depth (even) = (shallow side + deep side) ÷ 2 (sloping)volume = floor area × average depthone bag makes = area covered × depth it is quoted at, or the volume on the bagbags = ⌈volume × (1 + allowance) ÷ one bag⌉A bag’s yield is a volume. “42 sq ft at 1/8 in” means the mixed bag fills 42 square feet to a depth of an eighth of an inch, which is 0.4375 cubic feet. Converting it to a volume lets the page work at any depth, instead of only the depths a chart lists.
Measuring the floor
Measure the room wall to wall, including under anything that will be removed. For the depth, set a laser or long straightedge at the finished height and measure down to the floor at its highest and lowest points. The highest point sets the shallow side, often close to nothing.
Limits
This is a quantity estimate. It does not judge whether a floor needs leveling, which primer a slab or subfloor needs, or whether the finished floor meets a flooring maker’s flatness requirement. Follow the underlayment maker’s instructions for preparation, depth limits and curing.
With your numbers
- Volume = 200 ft² × 0.25 in = 4.167 ft³
- One bag makes 0.4375 ft³
- Bags = ⌈4.167 ft³ ÷ 0.4375 ft³⌉ = 10
Quick reference
No allowance by default; bags round up. Floors that dip or a porous slab can take more than the average depth suggests.
| Job | Bags to buy |
|---|---|
| 200 sq ft at 1/4 in, bag covers 42 sq ft at 1/8 in | 10 |
| 150 sq ft at 1/8 in, bag covers 46 sq ft at 1/8 in | 4 |
| 100 sq ft at 1/2 in, bag covers 42 sq ft at 1/8 in | 10 |
| Sloping floor, 0 to 1 in, 0.45 cu ft bags | 12 |
| Bathroom 8 × 5 ft at 3/8 in, bag covers 42 sq ft at 1/8 in | 3 |
| 12 m² at 5 mm, bag covers 4.2 m² at 3 mm | 5 |
| 20 m² at 10 mm, 12.5 L per bag | 16 |
Common questions about the Self-Leveling Underlayment Calculator
- How many bags of self-leveler do I need?
- Multiply the floor area by the average depth to get the volume, then divide by what one bag makes. Makers print the yield as an area at a depth: SikaLevel’s page gives 42 sq ft at 1/8 in per 50 lb bag, and Custom’s LevelQuik RS data sheet gives 46 to 48 sq ft at 1/8 in. Doubling the depth halves the area a bag covers.
- How do I work out the depth for a floor that is out of level?
- Find the high and low points with a long level or a laser. If the floor falls fairly evenly from one side to the other, the average depth is halfway between the shallowest and deepest pour, which is what the sloping option uses. A floor with a single hollow in the middle is closer to its shallow depth over most of the room, so measure the hollow separately.
- Why did I run out of self-leveler?
- Usually because the floor was lower in places than measured, the slab soaked some up, or material was left in the bucket and on the tools. Coverage figures leave these out: SikaLevel says its figures do not include an allowance for surface profile, porosity or waste. Choose Custom under More options to add a margin.
- How thin or thick can I pour it?
- That depends on the product. Each data sheet states its own range in one pour, and some allow thicker pours with added aggregate. Check the product you buy; this page only does the quantity.