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Brick Initial Rate of Absorption (IRA) Calculator

Compute a brick's Initial Rate of Absorption from a 1-minute water absorption test, per ASTM C67.

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

Initial Rate of Absorption

15 g/min/30in²

High confidence

Within the typical range where pre-wetting usually isn't required, though local practice and mortar type can still call for it in some conditions.

Mass absorbed
15 g

At the values currently entered, the initial rate of absorption works out to 15 g/min/30in². Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Add the equipment this sizes

This result is a specification — 15 g/min/30in² — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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

  • ASTM C67 Initial Rate of Absorption test: IRA = (wet mass − dry mass) x (30 / test area), reported in grams per minute per 30 in² of brick surface

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Frequently asked questions

Why does IRA matter for masonry construction?
A brick with a high IRA pulls water out of fresh mortar quickly, which can leave the mortar too dry to properly hydrate and bond — pre-wetting the brick (without saturating it) slows this water loss and improves the mortar bond.
What's considered a 'high' IRA?
A commonly cited threshold is 30 g/min/30in² — bricks above this are typically recommended for pre-wetting; the exact threshold can vary by mortar type and local practice.
Should bricks ever be tested wet already (not pre-dried)?
The standard ASTM C67 procedure starts from an oven-dried condition — testing from an already-wet or ambient-moisture condition would give an inaccurate (understated) IRA reading.