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Floor Drain Slope Screed Volume Calculator

Calculate the screed/mortar volume needed to slope a floor toward a central drain.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Screed volume needed

10.57 gal

Check your inputs

Assumes a simple linear slope from the perimeter down to a single central drain — a floor with multiple drains or a non-uniform slope will need a more detailed volume takeoff.

With the figures above, the screed volume needed comes to 40. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

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.

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 — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • For a floor sloping linearly from a maximum depth at the perimeter down to zero at a central drain, the average depth across the area is half the maximum depth, so screed volume = area × (maximum depth ÷ 2)

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Frequently asked questions

Why is the average depth half the maximum depth?
The screed tapers linearly from its maximum thickness at the perimeter down to zero right at the drain, so across the whole sloped area the average thickness works out to exactly half of the maximum thickness.
How is the maximum depth determined?
It depends on your required slope (commonly about 2%, or 1:50) and the distance from the drain to the farthest point on the perimeter — a longer run to the drain at the same slope needs a greater maximum depth.
Does this work for a floor with more than one drain?
No — this assumes a single central drain with a uniform linear slope from the perimeter. A floor with multiple drains or an irregular slope pattern needs a more detailed, section-by-section volume takeoff.