How this calculator works
Self-leveling underlayment is sold by weight but used by volume. A 50 lb bag makes about 0.48–0.5 cubic feet of mortar, which is about 23–24 sq ft at 1/4 in, or 46–48 sq ft at 1/8 in (Custom Building Products’ LevelQuik coverage). The calculator multiplies area by depth, adds waste and divides by the bag yield.
For a floor that slopes, use the thinnest and thickest points — the average depth sets the volume.
Volume (cu ft) = area × (depth ÷ 12) × (1 + waste)
Sloped floor: depth = (thinnest + thickest) ÷ 2
Bags = volume ÷ yield per bag (≈ 0.48 cu ft)
Assumptions and tips
- Assumes a flat-bottomed pour of uniform average depth; dips and low spots add volume.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Floor area | 120 sq ft |
| Depth | Average depth |
| Average depth | 0.25 in |
| Yield per 50 lb bag | 0.48 cu ft |
| Waste allowance | 10 % |
| Result | Value |
|---|---|
| 50 lb bags | 6 bags |
| Volume | 2.75 cu ft |
| Coverage per bag at this depth | 23 sq ft |
| Average depth used | 0.25 in |
| Total weight | 300 lb |
Step by step:
- Depth = 0.25 in
- Volume = 120 × (0.25 ÷ 12) × 1.1 = 2.75 cu ft
- Bags = 2.75 ÷ 0.48 = 5.73 → 6
Bags of self-leveler for 100 sq ft (10% waste)
Calculated with this tool at 0.48 cu ft per 50 lb bag.
| Average depth | 50 lb bags | Coverage per bag at this depth |
|---|---|---|
| 0.125 in | 3 bags | 46.1 sq ft |
| 0.25 in | 5 bags | 23 sq ft |
| 0.375 in | 8 bags | 15.4 sq ft |
| 0.5 in | 10 bags | 11.5 sq ft |
| 0.75 in | 15 bags | 7.7 sq ft |
| 1 in | 20 bags | 5.8 sq ft |
Common mistakes to avoid
- Skipping the primer — the leveler loses water into the subfloor and cracks or doesn’t bond.
- Mixing too few bags and running out halfway; pour the whole area in one go.
Frequently asked questions
How much does a 50 lb bag of self-leveler cover?
About 23–24 sq ft at 1/4 in, 46–48 sq ft at 1/8 in, and 11.5–12 sq ft at 1/2 in.
How many bags for 120 sq ft at 1/4 inch?
About 6 bags with 10% waste.
Can I pour self-leveler over plywood?
Many products allow it with primer and metal lath; check the product’s data sheet for minimum depth over wood.
Sources
Built and reviewed by Anirban Kundu, Creator & Editor · M.Sc Physics, 20 years teaching science