How many bags of self-leveling underlayment do I need?

Multiply the room length by width to get the area, add 10% for waste and divide by the coverage of one bag at your pour depth. A 50 lb bag of LevelQuik RS covers about 46 sq ft at 1/8 in, 23 sq ft at 1/4 in and 11.5 sq ft at 1/2 in. A 12 × 15 ft floor (180 sq ft, 198 with waste) takes 5 bags at 1/8 in, 9 at 1/4 in and 18 at 1/2 in. Round up: a pour that runs out part way leaves a cold joint.

How much does a 50 lb bag of self-leveler cover?

About 46 to 48 sq ft at 1/8 in, per Custom Building Products for LevelQuik RS, and Mapei lists up to 48 sq ft for a 50 lb bag of Ultraplan 1 Plus. At 1/4 in that halves to about 23 to 24 sq ft, and at 1/2 in to about 12. One bag makes roughly 0.48 to 0.5 cu ft of mix, whatever the depth. Bags of other sizes or brands differ, so use the coverage on your bag.

What thickness should I pour self-leveling underlayment?

Use the depth your flooring maker and the compound’s data sheet call for. Most are poured from a featheredge up to 1/2 in or 1 in in one pour (Ultraplan 1 Plus is rated featheredge to 1 in), and some take 1-1/2 in neat or more with aggregate. For a floor that is only out of flat, the average depth is what sets the bag count: a 1/8 in coat over most of it plus a deep low corner averages out to well under the depth of the corner. Pouring thicker than needed wastes bags and can crack or delay drying, and thinner than the minimum can fail to flow or bond.

How do I work out the average depth?

Lay a long straightedge or level across the floor in several places and measure the gaps. The pour surface sits at or above the highest spot, so the depth at each point is its gap to that level plus the minimum coat. Average those depths over the whole floor: if most of the floor needs the minimum 1/8 in and a tenth of it dips another 3/8 in, the average is about 1/8 + 3/80 in, a little under 3/16 in. Pick the closest depth in the list, and round up if you are unsure.

Why does the calculator give a volume as well as bags?

The volume is the cubic feet of mixed underlayment to pour: area with waste × depth. The 4.1 cu ft in the lead example is 117 litres. It lets you check a quote or compare a bagged product that has a different yield: divide it by the cu ft one bag makes. It is also what you would compare with a pump-truck or bulk quote. Wet and dry volumes are not the same, so the bag count is the number to buy.

How much waste should I allow?

About 10% for a sound, primed, flat-ish floor: it covers mix left in the bucket and mixer, spills and a slightly low spot. About 20% for a rough, porous or very uneven floor, or a pour with many walls and doorways to dam. These are planning estimates, not manufacturer figures. You can also add a bag when the count is close to a whole number, since a short pour is worse than a spare bag.

Do I need primer, and does it change the bag count?

Yes for most porous slabs and wood subfloors: the data sheets call for the maker’s primer so the slab does not draw water out of the mix and so the bond is good. Primer is not part of the bag count, but a slab that is not primed can lose enough water to shorten the flow time and cut real coverage. Follow your product’s data sheet for the primer, the water ratio per bag and the pour time.

Can I put tile or vinyl plank over self-leveling underlayment?

Yes. Once it has cured to the data sheet’s time (often a few hours for rapid-setting products, longer for thick pours) it is a flat base for tile, vinyl plank, laminate and hardwood. Use the thinset and tile calculators for the next layer, and the underlayment calculator if the floor also needs a foam or cork underlayment. Check the flooring maker’s limit on moisture in the underlayment before laying.

Self-Leveling Underlayment Calculator: How Many Bags Do I Need?

Bags of self-leveling underlayment = floor area × 1.10 ÷ what one bag covers at your pour depth. A 12 × 15 ft floor is 180 sq ft, or 198 sq ft with 10% waste. A 50 lb bag of Custom LevelQuik RS covers about 46 sq ft at 1/8 in, so about 23 sq ft at 1/4 in: that is 9 bags, about 4.1 cu ft of mix. At 1/8 in it is 5 bags and at 1/2 in 18. Coverage is inversely proportional to depth: double the thickness and you need twice the bags.

Figures based on the sources listed belowUpdated 2026-10-07How we calculate

Room length

Room width

Waste allowance

Standard (+10%)Rough, porous or very uneven floor (+20%)Custom

Product and bag sizeSets how far a bag goes at 1/8 in. Products differ by a few sq ft per bag: use the figure on your bag.

Average pour thicknessThe average depth over the whole floor, not the shallowest spot. Check the low and high spots first: a floor that dips 1/2 in in one corner takes far more than its flat part. Stay within the maker’s minimum and maximum for the product.

Price per bag (optional)

Buy 9 bags

180 sq ft + 10% waste = 198.00 sq ft

Mix to pour (with waste): 4.13 cu ft
One 50 lb bag covers: 23 sq ft (2.14 m²) at this depth, 0.48 cu ft of mix

Low

$252.00

Expected

$360.00

High

$540.00

Includes 18.00 sq ft waste

How this number is calculated

180 sq ft + 10% waste = 198.00 sq ft ÷ 23 sq ft per bag = 9 bags

Next step in your project

Thinset Mortar Calculator
Thinset to set tile over the leveled floor. Opens with your 12 × 15 ft filled in.
Vinyl Plank Flooring Calculator
Vinyl plank for the same floor. Opens with your 12 × 15 ft filled in.

Shopping list

Self-leveling underlayment (50 lb bag)
Primer for self-leveling underlayment
Gauge rake for self-leveler
Spiked shoes for walking on wet leveler
Mixing paddle (drill attachment)
Foam sill seal tape (perimeter dam)
5-gallon bucket

Show diagram

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Coverage per bag by pour depth

Sq ft one bag covers, and bags per 100 sq ft before waste, at each depth. Worked from each product’s coverage at 1/8 in (46 sq ft for LevelQuik RS 50 lb, 48 for Ultraplan 1 Plus 50 lb, 43 for Henry 555 40 lb) with coverage inversely proportional to depth. Check the data sheet for your product’s minimum and maximum depth.
Average depth	LevelQuik RS (sq ft)	Ultraplan 1 Plus (sq ft)	Henry 555 (sq ft)	LevelQuik RS (bags per 100 sq ft)	Ultraplan 1 Plus (bags per 100 sq ft)	Henry 555 (bags per 100 sq ft)
1/8 in	46	48	43	2.2	2.1	2.3
3/16 in	30.7	32	28.7	3.3	3.1	3.5
1/4 in	23	24	21.5	4.3	4.2	4.7
3/8 in	15.3	16	14.3	6.5	6.3	7
1/2 in	11.5	12	10.8	8.7	8.3	9.3
3/4 in	7.7	8	7.2	13	12.5	14
1 in	5.8	6	5.4	17.4	16.7	18.6

How many bags for a room

Worked by this calculator: Custom LevelQuik RS 50 lb bags (46 sq ft at 1/8 in), 10% waste, rounded up to whole bags.
Room	Floor area (sq ft)	Bags at 1/8 in	Bags at 1/4 in	Bags at 1/2 in
8 × 10 ft	80	2	4	8
10 × 12 ft	120	3	6	12
12 × 15 ft	180	5	9	18
14 × 16 ft	224	6	11	22
20 × 20 ft	400	10	20	39

Methodology & assumptions

Floor area is length × width in feet, less any area you will not pour, with the waste allowance added (10%, or 20% for a rough, porous or very uneven floor, which are estimates, not published figures). A bag’s coverage is its published coverage at 1/8 in scaled by thickness: coverage at depth = coverage at 1/8 in × (1/8 ÷ depth). That matches the manufacturers’ own charts, where coverage halves each time the depth doubles (Custom Building Products lists 46 to 48 sq ft per 50 lb bag at 1/8 in, 23 to 24 at 1/4 in and 11.5 to 12 at 1/2 in). The calculator uses the low end of a published range, and bags are rounded up. The volume of mix is area with waste × depth, shown in cubic feet (and m³ under the metric toggle); one bag makes about 0.48 cu ft at 46 sq ft per 1/8 in, which is the same at every depth. The depth is the average over the floor: measure the high and low spots with a straightedge and level, and use the mean, not the shallowest point. The products offered are examples, not a recommendation: the 46 sq ft figure is the low end of a published range, and the 48 sq ft (Mapei, 50 lb) and 43 sq ft (Henry, 40 lb) figures are the coverage on manufacturer product pages as listed by retailers, which we could not check against a data sheet, so use the coverage printed on your bag. Real coverage also falls with a thin or over-watered mix, porous slabs that soak up the primer coat, and mix left in the bucket.

Custom Building Products, LevelQuik RS (Rapid Setting) Self-Leveling Underlayment, technical data sheet TDS-108: coverage of a 50 lb bag by thickness (46 to 48 sq ft at 1/8 in)
Mapei, Ultraplan 1 Plus product page and technical data sheet: 50 lb bag, up to 48 sq ft at 1/8 in, featheredge to 1 in in one pour (coverage as listed by retailers; check the data sheet)
W. W. Henry, Henry 555 LevelPro Self-Leveling Underlayment product information sheet: 40 lb bag, 43 sq ft at 1/8 in (as listed by retailers; check the data sheet)
Typical US retail prices for a 40 to 50 lb bag of self-leveling underlayment, 2026 (estimate)
Waste allowances of 10% and 20% are planning estimates, not manufacturer figures

How to calculate how many bags of self-leveling underlayment you need

Measure the floor. Measure the length and width in feet. Add a second area if the floor is not a rectangle, and subtract any areas you will not pour.
Find the average pour depth. Check the floor with a long straightedge, find the highest spot and the low spots, and work out the average depth over the whole floor. Pick the closest depth from 1/8 to 1 in.
Pick a product and a waste allowance. Choose a product (or use the coverage on your bag) and a waste allowance: 10% for a sound floor, 20% for a rough or very uneven one.
Read the bags and the coverage. The calculator divides the area with waste by the coverage of one bag at your depth (the 1/8 in coverage × 1/8 ÷ depth) and rounds up. It also shows the volume of mix to pour.
Plan the pour. Prime the floor, dam the doorways, mix and pour in one go, and have enough bags and mixers on hand to keep the pour wet from edge to edge.

Worked examples

Project	Result
12 × 15 ft floor, 1/4 in average, LevelQuik RS	180 sq ft + 10% waste ≈ 198 sq ft → 9 bags
10 × 12 ft bathroom, 1/8 in skim coat, LevelQuik RS	120 sq ft + 10% waste ≈ 132 sq ft → 3 bags
20 × 20 ft room, 1/2 in average, rough floor (20% waste), Ultraplan 1 Plus	400 sq ft + 20% waste ≈ 480 sq ft → 40 bags
8 × 10 ft room, 3/8 in average, Henry 555 40 lb bags	80 sq ft + 10% waste ≈ 88 sq ft → 7 bags

Frequently asked questions

How many bags of self-leveling underlayment do I need?: Multiply the room length by width to get the area, add 10% for waste and divide by the coverage of one bag at your pour depth. A 50 lb bag of LevelQuik RS covers about 46 sq ft at 1/8 in, 23 sq ft at 1/4 in and 11.5 sq ft at 1/2 in. A 12 × 15 ft floor (180 sq ft, 198 with waste) takes 5 bags at 1/8 in, 9 at 1/4 in and 18 at 1/2 in. Round up: a pour that runs out part way leaves a cold joint.
How much does a 50 lb bag of self-leveler cover?: About 46 to 48 sq ft at 1/8 in, per Custom Building Products for LevelQuik RS, and Mapei lists up to 48 sq ft for a 50 lb bag of Ultraplan 1 Plus. At 1/4 in that halves to about 23 to 24 sq ft, and at 1/2 in to about 12. One bag makes roughly 0.48 to 0.5 cu ft of mix, whatever the depth. Bags of other sizes or brands differ, so use the coverage on your bag.
What thickness should I pour self-leveling underlayment?: Use the depth your flooring maker and the compound’s data sheet call for. Most are poured from a featheredge up to 1/2 in or 1 in in one pour (Ultraplan 1 Plus is rated featheredge to 1 in), and some take 1-1/2 in neat or more with aggregate. For a floor that is only out of flat, the average depth is what sets the bag count: a 1/8 in coat over most of it plus a deep low corner averages out to well under the depth of the corner. Pouring thicker than needed wastes bags and can crack or delay drying, and thinner than the minimum can fail to flow or bond.
How do I work out the average depth?: Lay a long straightedge or level across the floor in several places and measure the gaps. The pour surface sits at or above the highest spot, so the depth at each point is its gap to that level plus the minimum coat. Average those depths over the whole floor: if most of the floor needs the minimum 1/8 in and a tenth of it dips another 3/8 in, the average is about 1/8 + 3/80 in, a little under 3/16 in. Pick the closest depth in the list, and round up if you are unsure.
Why does the calculator give a volume as well as bags?: The volume is the cubic feet of mixed underlayment to pour: area with waste × depth. The 4.1 cu ft in the lead example is 117 litres. It lets you check a quote or compare a bagged product that has a different yield: divide it by the cu ft one bag makes. It is also what you would compare with a pump-truck or bulk quote. Wet and dry volumes are not the same, so the bag count is the number to buy.
How much waste should I allow?: About 10% for a sound, primed, flat-ish floor: it covers mix left in the bucket and mixer, spills and a slightly low spot. About 20% for a rough, porous or very uneven floor, or a pour with many walls and doorways to dam. These are planning estimates, not manufacturer figures. You can also add a bag when the count is close to a whole number, since a short pour is worse than a spare bag.
Do I need primer, and does it change the bag count?: Yes for most porous slabs and wood subfloors: the data sheets call for the maker’s primer so the slab does not draw water out of the mix and so the bond is good. Primer is not part of the bag count, but a slab that is not primed can lose enough water to shorten the flow time and cut real coverage. Follow your product’s data sheet for the primer, the water ratio per bag and the pour time.
Can I put tile or vinyl plank over self-leveling underlayment?: Yes. Once it has cured to the data sheet’s time (often a few hours for rapid-setting products, longer for thick pours) it is a flat base for tile, vinyl plank, laminate and hardwood. Use the thinset and tile calculators for the next layer, and the underlayment calculator if the floor also needs a foam or cork underlayment. Check the flooring maker’s limit on moisture in the underlayment before laying.

Handy tools

Decimal to Fraction Converter: Turn a depth measured as a decimal, such as 0.4375 in, into the nearest 1/16 and pick the closest depth above.
Feet and Inches Calculator: Add up room lengths measured in feet, inches and fractions, and get decimal feet for the fields above.