Self-leveling concrete calculator

How many bags of self-leveling underlayment a floor takes comes down to area and the average fill depth — not the 1/8 inch on the bag. Enter both and get bags to order, with the depth check most calculators leave out.

01 How the math works

Bag count for self-leveling underlayment is a volume problem with one twist. Work out the volume of leveler the floor needs, then divide by what a bag yields. The twist is the depth: the figure on the bag is a coverage at a reference thickness, almost always 1/8 in (3 mm), and coverage scales inversely with how deep you actually pour.

The coverage-to-yield step is a straight identity: a bag rated 47 ft² at 1/8 in lays 47 × (0.125 ÷ 12) = 0.49 ft³ (0.0139 m³) of material. Pour that same bag at 1/4 in and it covers 23.5 ft² (2.18 m²) — half the floor, because you put down twice the thickness. That is the whole reason average depth, not the reference thickness, drives the order.

Coverage figures are bag-specific. A 50 lb bag of LevelQuik RS is rated 46–48 ft² at 1/8 in; Mapei Self-Leveler Plus runs about 48 ft²; Henry 555 LevelPro is a 40 lb bag at about 43 ft². Read the figure off the bag you are buying — the field defaults to the LevelQuik RS midpoint of 47 ft².

02 Worked example

Take a 10 ft × 12 ft room (3.05 m × 3.66 m), 120 ft² (11.15 m²), with a subfloor that dips enough to need an average fill of 1/4 in (6.35 mm) — not a nominal 1/8 in skim.

Fill volume is 120 × (0.25 ÷ 12) = 2.5 ft³ (0.0708 m³). At the LevelQuik RS yield of 0.49 ft³ per 50 lb bag, add a 10% waste factor and round up: 2.5 × 1.10 ÷ 0.49 = 5.6 → 6 bags.

Size the same floor at a nominal 1/8 in instead and you get 120 ÷ 47 = 3 bags — exactly half the order, because the depth doubled. A floor flat enough to need only 1/8 in rarely needs leveling in the first place, which is why the nominal figure under-orders almost every real pour.

03 When this calculator is wrong

The number this calculator leans on hardest is the average fill depth, and that is the number easiest to get wrong. Self-leveling underlayment is poured to correct a floor that is out of flat, so the depth is not uniform — it runs from featheredge at the high spots to the deepest low. Guess a single thickness and the bag count is a guess too.

• Average depth, measured, not nominal. Snap a grid across the room, pull a stringline or laser to the finish plane, and measure the gap at each point. The average of those gaps is the depth to enter — not 1/8 in because that is what the bag quotes. On a floor that averages 1/4 in, sizing at 1/8 in orders half the bags you need.
• Check the depth against the single-pour maximum. Neat (un-aggregated) self-leveler has a ceiling per pour: 1.5 in (3.8 cm) for LevelQuik RS, 1 in (25 mm) for Mapei Self-Leveler Plus. A bag count at a greater average depth is a number you can't place in one lift — the pour has to be built in lifts or, where the data sheet allows it, extended with pea gravel. LevelQuik RS is not rated for aggregate. The calculator flags the entered depth against the 1.5 in LevelQuik RS limit.
• It levels, it doesn't fall to a nominal thickness. Self-leveler seeks a flat horizontal plane, so over a sloped or dished subfloor the depth varies across the room by design. The volume you need is set by the fill you are adding to reach that plane, which is why the grid average — not the thinnest or the thickest spot — is the honest input.
• It's leveler only. The bag count here is underlayment, nothing else. Primer is sold and ordered separately, and most cement-based self-levelers require it over a porous or non-porous subfloor to stop pinholing and bond failure. The calculator doesn't size primer, perimeter foam, or the flooring that goes on top.

04 What to do with the result

Order the rounded-up bag count in one trip, and lean toward the high side of your depth estimate rather than the low. The cost of a spare bag on the shelf is small. The cost of running short is not: rapid-set self-leveler has a working time measured in minutes, and a second batch mixed after the first has started to set lands as a visible cold joint or a ridge where the two pours met. Running out mid-floor is the one failure the material won't forgive.

If your bag quotes a coverage figure at a thickness other than 1/8 in, or quotes a cubic-foot yield directly, you can still use this calculator: convert the figure to coverage at 1/8 in first (double the ft² for a 1/4 in rating, quadruple it for 1/2 in), or divide the stated yield in cubic feet by 0.0104 to get the equivalent 1/8 in coverage. The bag count the calculator returns is only as good as the coverage figure you feed it, so take that number off the data sheet, not the front of the bag.

05 Common questions

How much self-leveling concrete do I need for a room?

A 10 × 12 ft (120 ft² / 11.15 m²) room filled to a 1/4 in (6.35 mm) average takes 2.5 ft³ (0.0708 m³) of leveler, or 6 50 lb bags at the LevelQuik RS yield with 10% waste. Change the average depth and the bag count moves with it, one-for-one.

How many square feet does a bag of self-leveler cover?

Only at a stated thickness. A 50 lb bag rated 47 ft² at 1/8 in covers 23.5 ft² at 1/4 in and 11.75 ft² at 1/2 in — coverage halves each time the depth doubles. A coverage number with no thickness attached tells you nothing.

How thick can you pour self-leveling concrete in one pour?

It depends on the product. Neat LevelQuik RS goes featheredge to 1.5 in (3.8 cm) in a single pour; Mapei Self-Leveler Plus caps at 1 in (25 mm). Deeper than the maximum means building in lifts or extending with aggregate where the data sheet permits — LevelQuik RS does not permit it.

How many 50 lb bags of self-leveler are in a cubic foot?

A 50 lb bag rated 47 ft² at 1/8 in yields about 0.49 ft³ (0.0139 m³), so a cubic foot takes roughly 2 bags. Self-leveler is lighter per cubic foot than standard premix concrete — about 0.0098 ft³ per pound against 0.0075 — so don't borrow a concrete bag figure for it.

Why does the calculator ask for average depth instead of thickness?

Because a self-leveling pour almost never has one thickness. It fills a floor that is out of flat, so the depth runs from nothing at the high spots to the deepest low. The volume — and the bag count — follows the average fill across the room, which is the number a single "thickness" field quietly gets wrong.