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The brick's weight before the absorption test.
Oven-dried to constant weight, which is what "dry" means here — not simply taken off a dry-looking pallet. A brick that has already absorbed moisture from a damp stack has taken up part of what the test is trying to measure, so the result comes out LOW: it reads as a brick that does not need wetting before laying, which is the more damaging direction to be wrong in.
The brick's weight after 1 minute of partial water immersion (per ASTM C67 procedure).
The minute is the test, not a guideline. Absorption is fastest at the very start and then slows, so a brick left in for two minutes produces a number that describes a different experiment and cannot be compared with anyone else's. Wipe the surface water off before weighing — a film of water on the face is not absorption, and on a large brick it is enough to move the answer.
The actual bed surface area of the brick tested.
Standard modular brick is close to the 30 in² reference area; measure your specific brick's actual bed area for accuracy.
Initial Rate of Absorption
15 g/min/30in²
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
They open the calculator with your figures already in it
Brick Initial Rate of Absorption (IRA) Calculator: 15 g/min/30in² — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- 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
Inputs used
- Dry Brick Weight (g)
- 500
- Weight After 1 Minute Partial Immersion (g)
- 515
- Test Surface Area (in²)
- 30
Intermediate steps
- Mass absorbed
- 15 g
Confidence note: 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.
What this calculation does not cover
- One specimen, one number. ASTM C67 works from a set of units and an average, and suction varies from brick to brick within a pallet and considerably more between deliveries — this result does not describe the rest of the load.
- The calculator sees two masses and an area and nothing else. It cannot tell whether the specimen was genuinely oven-dry and cooled, whether the water was held at the standard depth for the full minute, or whether the wet face was blotted before weighing, and each of those moves the mass gain.
- The test area is used exactly as typed. Nothing checks that it is the bed face you actually stood in the water, or that cores and frogs are treated the way your specification treats them — and leaving the field on the 30 in² (194 cm²) reference for a brick whose bed face is smaller than that understates the result.
- Only high suction is flagged. A very low IRA — dense engineering or glazed units that take up almost nothing — is its own problem: mortar that stays wet, stiffens slowly and lets the units float and bleed down the face. The calculator also does not say how long to dock a thirsty brick, and an over-wetted, streaming brick is worse on the bed than a dry one.
- IRA is a wetting-policy number, not a performance rating. It does not predict bond strength, and it says nothing about rain resistance, freeze-thaw durability, efflorescence or compressive strength — those are separate tests. The 30 g/min/30in² line is common practice rather than a code requirement, so where a project specification sets the threshold, that governs; a European specification written to BS EN 772-11 asks for a water absorption coefficient measured and reported differently, and this figure is not that value.
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.
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 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- 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
Which documents these citations point at
Standards referenced: ASTM C67 (ASTM International, United States).
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 brick and mix mortar. 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.
- Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
- Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
- 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 9 tools this job needsHide tools
Essential
Brick trowel and jointer
Mixing bucket or tub
Shovel and spade
Spirit level
String line and pins
Tape measure
Wheelbarrow
Recommended
Angle grinder
Cement mixer
Also needed as materials: cutting and diamond discs.
what each masonry tool is for, and the spec that decides which to buy where one does.