Self Leveling Underlayment Calculator

Turn area, average depth and your bag yield into bags to order and primer volume, and see how far the order moves if the average depth is out.

How Many Bags Does This Floor Take?

Enter the area, the average depth across the pour, and the bag yield off your product's data sheet. The calculator returns bags to order with waste included, what one bag covers at your depth, primer volume, and what the order becomes if your average depth is out by a sixteenth of an inch. It seeds no product data: bag yields differ by more than 20% between products, so yours has to come off the bag.

Take the bag yield off the bag. Yields differ by more than 20% between products that look identical on the shelf, so this tool ships no default and asks you for yours. It also will not guess your product’s minimum or maximum pour depth, and both are limits worth reading before you mix.

The Slab

Area, and the average depth across it. Average, not the deepest point.

Units
Only the part getting underlayment. Not sure? Work it out with the Area Calculator.
The mean across the whole pour, not the low spot. Take readings on a grid and average them: this one number sets the order, and it is where short orders come from.

The Product

Data sheets state the yield two ways. Use whichever one yours prints.

Printed on the bag and the data sheet. Read it for the bag size you are actually buying.
What stays in the barrel and the bag, and what runs into a joint. 10% is a common starting point rather than a measured figure.
From the primer’s own data sheet, at its dilution. Add it to size the primer in the same pass. Underlayment over bare concrete is not a one product job.

Enter the area, the average depth, and your product’s bag yield to see the order.

How the Self Leveling Underlayment Calculator Works

  1. Choose imperial or metric
  2. Enter the area you are pouring, and the AVERAGE depth across it rather than the depth of the low spot
  3. Pick the form your data sheet uses: a volume per bag, or a coverage figure at a stated depth
  4. Enter that yield. If your sheet gives coverage, enter the depth it is quoted at as well
  5. Adjust the waste allowance, and add a primer coverage rate to size the primer in the same pass
  6. Read the bags to order, and check the depth sensitivity panel before you place it

Examples

Scenario800 ft² garage, 1/4 in average depthInputSheet says 0.45 ft³ per bag · 10% waste · primer 300 ft²/galResult41 bags · 2.67 gal primer
Scenario75 m² floor, 6 mm average depthInputSheet says 12.7 L per bag · 10% wasteResult39 bags · 495.00 L
Scenario500 ft² at 1/8 in, sheet quotes coverage not volumeInputSheet says 24 ft² at 1/4 in · 10% wasteResult12 bags · one bag covers 48.0 ft²
ScenarioThat same 800 ft² garage, average depth out by 1/16 inInput3/16 in against 5/16 inResult31 bags against 51 bags

Frequently Asked Questions

How many bags of self leveling underlayment do I need?

Bags come from three numbers: the area, the average depth, and how much volume one bag yields. The first two are yours and the third is on the bag. Multiply area by average depth to get a volume, add a waste allowance, divide by the bag yield, and round up. An 800 ft² garage at a quarter inch average is 16.67 ft³ of underlayment before waste, which is 41 bags of a product yielding 0.45 ft³. Enter your own figures above rather than borrowing that yield: it is a round number chosen to show the arithmetic, not a product spec.

What does average depth mean, and how do I measure it?

It is the mean depth across the whole pour, not the depth of the worst dip. Set a straightedge or a laser across the slab, take readings on a grid rather than at a few spots that caught your eye, and average them. This is the number that decides the order and it is the one people guess. On a quarter inch pour, being out by a sixteenth of an inch moves an 800 ft² job from 41 bags to 51, or down to 31 the other way. The calculator shows both so the size of that risk is in front of you before you order.

Why does one bag cover twice the area at half the depth?

Because coverage is volume divided by depth, and nothing else. A bag holding half a cubic foot covers 24 ft² at a quarter inch and 48 ft² at an eighth. That is why a coverage figure with no depth attached to it is not a specification, and why this calculator asks for the depth your sheet quotes its coverage at. Reading a coverage figure quoted at an eighth and pouring a quarter is how an order comes out at half what the job needs.

Do I have to prime before self leveling underlayment?

Over bare concrete, effectively always. An unprimed slab pulls water out of the mix as it flows, which kills the flow before it has levelled and leaves pinholes where escaping air had nowhere to go. Primer also stops the underlayment from bonding to dust rather than to concrete. The rate and dilution are on the primer's own data sheet, and they change with how porous the slab is, so enter yours in the optional field and the calculator sizes it over the same area.

How thick can self leveling underlayment be poured?

That is a product limit, not a general one, and both ends of it matter. Every product has a minimum below which it will not flow out and cure properly, and a maximum per lift above which it can crack or fail to cure through. Some are rated to feather to nothing at the edge and some are not. Those numbers are on the data sheet for the product you bought and this site will not guess them for you, because a thickness limit invented for a third party's product is exactly the kind of claim our methodology forbids.

Is this the same as a self leveling epoxy?

No, and they solve different problems. This calculator is for a cementitious underlayment: a bagged powder mixed with water and poured to level an uneven slab before anything else happens to it. A self leveling epoxy is a resin coating that goes on afterwards, is sold in kits rather than bags, and is sized by coverage rate. For that one, use the Epoxy Coverage Calculator.

Why does the calculator not have a product list?

Because bag yields vary by more than 20% between products that look identical on a shelf, and a default nobody can cite would quietly decide your order. The yield is printed on the bag and on the data sheet, it takes a moment to read, and it is the difference between the right number of pallets and a job that stops halfway.

Important Notes

  • Average depth is the single largest source of a short order on this job, because bags scale with it exactly
  • Bag yield is a volume, so it does not change with depth: what changes is the area that volume covers
  • The waste allowance covers what stays in the barrel and the bag, and what runs into joints and cracks
  • Fill large voids and cracks separately before the pour rather than letting the underlayment find them
  • Underlayment is sold in whole bags, so the answer is always rounded up
  • Minimum and maximum pour depths are product limits and live on your data sheet, not here
Square Meter & Square Foot CalculatorWork out the area of the pour before you size the bags.Crack Repair CalculatorSize the filler for cracks and voids that should be dealt with before the pour.Epoxy Coverage CalculatorSize the coating that goes on once the slab is level.Concrete Moisture CalculatorCheck the slab is dry enough before you pour anything onto it.Grinding Time CalculatorEstimate the prep pass that opens the slab for the primer.
How Much Self Leveling Underlayment Do You NeedBags come from area, average depth and bag yield. Only one of those is printed on anything, and the other two decide the order.

Where the Number Actually Comes From

A bag of self leveling underlayment is sold by the volume it yields, not by the area it covers, and that is the whole reason this calculation trips people up. Coverage is yield divided by depth, so the same bag that covers 24 ft² at a quarter inch covers 48 ft² at an eighth and 12 ft² at a half. A coverage figure printed without the depth it was measured at tells you nothing, and taking one at face value is how an order ends up at half or double what the floor needs. The other half of the problem is that the depth is not a specification at all. It is a property of the slab you are standing on, nobody publishes it, and it has to be measured. Take readings across a grid and average them, because an average pulled from the few dips that caught your eye is biased deep, and one taken from the flat parts is biased shallow. Bags scale with that average exactly, so on a quarter inch pour a sixteenth of an inch of error is a quarter of the order.