Self-Leveling Compound Calculator — Bags for Concrete or Plywood
Get the number of 50-lb bags for a uniform pour, a floor that slopes to one side, or a single low spot. Over plywood the calculator applies the minimum thickness the subfloor requires, which is usually what decides the bag count, and adds the metal lath you will need.
Why Plywood Changes the Bag Count
On concrete you pour only as deep as the floor needs, down to about 1/8 inch. A wood subfloor moves under load, so the leveler has to be thick enough to bridge that movement without cracking. Manufacturers set a minimum thickness for wood, and it applies over the whole floor, including the high spots. If your floor only needs a skim of 1/8 inch, you still pour the minimum.
| Subfloor | Minimum thickness | Bags per 100 sq ft |
|---|---|---|
| Concrete | 1/8 in | 3 |
| 3/4 in plywood or OSB + lath, joists 16 in apart | 3/8 in | 7 |
| Same, joists 20 in apart | 1/2 in | 10 |
| Same, joists 24 in apart | 5/8 in | 12 |
| Two layers of plywood, no lath | 3/8 in | 7 |
Minimums from TEC EZ Level's data sheet; USG Durock self-leveler asks for 1/2 in with lath or 3/4 in without. Check the bag of the product you buy. Bag counts at about 0.5 cu ft per 50-lb bag with 10% extra.
That is why the same low spot costs so much more on a wood floor. A dish-shaped dip 3/4 inch deep across 30 sq ft of a 150 sq ft concrete floor takes about 3 bags. On plywood with joists at 16 inches, the same floor takes about 13, because the whole room gets the 3/8-inch minimum first.
Pouring a Slope or a Single Low Spot
Few floors need an even layer. For a floor that slopes, measure the gap under a straightedge at the deep side; the leveler forms a wedge from that depth down to nothing, so its volume is half of a full-depth pour. For one low spot, measure its size and its deepest point; a dish-shaped hollow also holds about half the volume of a flat-bottomed one of the same depth. Both are estimates, so measure the deepest point carefully and round up rather than down.
If the high side of the floor is higher than you want the finished level to be, leveler cannot help: grind the high spot on concrete, or plane or sand it on wood, before pouring.
Before You Pour Over Wood
- The floor has to be stiff. At least 3/4 inch tongue-and-groove plywood or rated OSB on joists no more than 24 inches apart, with deflection no more than L/360. A bouncy floor cracks any leveler.
- Not over these. Particleboard, lauan plywood, hardboard, and old strip wood flooring are excluded on every data sheet we checked.
- Fasten and seal. Screw down loose panels, fill gaps and holes with patch so the liquid cannot run through, and fit foam or wood dams at doorways and stairs.
- Prime, then lath. Prime and let it dry to a clear film, then staple galvanized diamond lath with 2-inch overlaps, about every 6 inches at edges and 8 inches in the field. A 27 x 96 in sheet covers roughly 16 sq ft once overlaps are taken out.
- Leave a gap at the walls. 1/8 to 1/4 inch of foam around the perimeter lets the wood move.
Mixing and Working Time
Mix full bags with exactly the water the bag specifies (TEC EZ Level calls for 5.25 quarts per 50 lb) and never add more to make it flow: extra water weakens the surface and causes cracking and dusting. Working time is short, about 15 to 20 minutes at 70°F, so line up the bags, buckets and water before the first one is opened, and have a helper mix while you pour. Keep the room between 50 and 90°F, and on a radiant floor turn the heat off a couple of days before and keep it off for about a week after.
For the bigger decision of whether leveler or a new layer of plywood is the right fix for your floor, see self-leveling compound vs. plywood underlayment.
Frequently Asked Questions
Can you pour self-leveling compound on plywood?
Yes, on a stiff subfloor of at least 3/4 inch plywood or rated OSB, once it is primed and covered with metal lath, or over two layers of plywood without lath. The catch is the minimum thickness, typically 3/8 inch on joists 16 inches apart and more on wider spacing, which applies over the whole floor.
How many bags of self-leveler do I need for 100 sq ft?
About 3 bags for 1/8 inch on concrete, 5 for 1/4 inch, and 7 for the 3/8-inch minimum over plywood with lath, using roughly half a cubic foot per 50-lb bag and 10% extra.
Do I need metal lath for self-leveling compound over plywood?
On a single layer of plywood or OSB, yes for most products. Some allow you to skip lath on two layers of plywood, or at a thicker pour of about 3/4 inch, so read the data sheet for the product you are using.
How thin can self-leveling compound be over wood?
Usually 3/8 inch with lath on joists 16 inches apart, 1/2 inch at 20 inches and 5/8 inch at 24 inches, though some products ask for 1/2 inch regardless. On concrete most products go down to about 1/8 inch.