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Self-Leveling Underlayment (SLU) Volume Calculator

Calculate the self-leveling underlayment volume needed to correct subfloor roughness before flooring installation.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
The total subfloor area to be leveled.

Measure the room's length x width, or add up multiple sections for an irregular floor plan.

The average thickness of the self-leveling compound pour across the floor.

Self-leveling underlayment naturally flows thicker in low spots and thinner over high spots — estimate the average depth across the whole floor, not just the deepest point.

SLU volume needed

42.1 gal

Medium confidence

Actual SLU consumption depends on subfloor roughness/low spots — an uneven subfloor will consume more material than this average-depth estimate suggests. Order 10-15% extra for irregular subfloors.

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • SLU volume = floor area × average pour depth, the standard method for a self-leveling compound poured at a roughly uniform average thickness

Inputs used

Floor Area
270 sq ft
Average Pour Depth
0.25 in
Final result42.08 gal

Confidence note: Actual SLU consumption depends on subfloor roughness/low spots — an uneven subfloor will consume more material than this average-depth estimate suggests. Order 10-15% extra for irregular subfloors.

What this calculation does not cover

  • Litres do not buy anything. SLU is sold by the bag, and turning this volume into a bag count needs the product's own yield — the litres one bag makes at its specified water ratio — which runs roughly 12 to 16 litres (3.2 to 4.2 gal) from a 25 kg (55 lb) bag and varies enough between products to shift the bag count by 10% or more on the same floor. Take the yield off the data sheet rather than assuming a density.
  • The high spot sets the datum for the whole floor, and this takes an average instead. Every SLU has a minimum thickness it will flow and cure at, and you cannot pour thinner than that over the highest point — so nothing on the floor ends up thinner than that minimum and the low corner takes the minimum plus the whole deviation. There is also a maximum lift, above which the pour must be split or extended with aggregate, and adding aggregate changes the yield again.
  • Primer is a separate material with its own coverage rate, and skipping it is how a pour fails rather than how it saves money. A porous slab pulls water out of the compound and pinholes; a sealed or non-porous substrate gives it nothing to grip. Porous slabs often take two coats, and the primer rate per square metre has no relationship to the pour depth calculated above.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

self-levelling underlayment 0.25 inself-levelling underlayment 6.35 mmfloor slab

Part of bigger jobs

This trade is one line of several job takeoffs. Run the whole job and every other trade comes back with it, off the same measurements.

Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1
  1. SLU volume = floor area × average pour depth, the standard method for a self-leveling compound poured at a roughly uniform average thickness
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To lay a floor screed. Generic types, no brands, no prices.

Protection this work requires

  • Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
  • Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
  • Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
Show the 6 tools this job needs

Essential

  • Mixing bucket or tub

  • Screed bar or rail

  • Shovel and spade

  • Spirit level

Recommended

  • Moisture meter

  • Paddle mixer

what each flooring tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Called something else where you work? Screed · Self-levelling compound · Subfloor · Tolerance and permitted deviation · Impact sound insulation — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Screed vs Self-Levelling Compound — the factors that actually differ, with no invented prices.

Worked example: Vinyl plank floor — step 2 of 7

Already gone wrong? My screed has cracked · A white powder or bloom keeps appearing on my concrete floor · My laminate or engineered floor is lifting, peaking or gapping

How to calculate self-leveling underlayment (SLU) volume in 3 steps

  1. Floor AreaThe total subfloor area to be leveled.
  2. Average Pour DepthThe average thickness of the self-leveling compound pour across the floor.
  3. SLU volume neededThe tool computes the SLU volume needed from those figures and shows the formula, its sources, and a confidence rating alongside it.

SLU volume needed by floor area

Page defaults, not your figures above.

Floor AreaSLU volume needed (gal)
200 sq ft29.5
300 sq ft44.2
400 sq ft58.9
500 sq ft73.6

Frequently asked questions

Why use an average depth instead of a fixed pour thickness?
Self-leveling underlayment is designed to flow and self-level, so it naturally sits thicker over low spots and thinner over high spots. An average depth across the whole floor gives a more realistic total volume than assuming a single uniform thickness.
Should I order extra material beyond this estimate?
Yes — an uneven subfloor with significant low spots will consume more material than an average-depth estimate suggests. Ordering 10-15% extra is a reasonable allowance for irregular subfloors.
How do I estimate my subfloor's average pour depth?
Check several points across the floor with a straightedge and measure the gap to identify high and low spots, then estimate a reasonable average depth that accounts for the low spots needing more material.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.