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ACI 347 Wall Formwork Rate-of-Placement Pressure Calculator

Calculate the maximum lateral pressure on wall formwork from ordinary (non-SCC) concrete, using the ACI 347R rate-of-placement formula.

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 2026-08-27 · v1.2.0

Market
Imperial · sales tax
9.84 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Maximum lateral formwork pressure

1003.69 psf

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Wall pressure is rate-limited rather than height-limited. Because a wall is filled over a long period, the concrete at the base normally stiffens before the top arrives, and the pressure envelope caps out well below full hydrostatic.

Unit weight coefficient Cw
1.03 (dimensionless)
Full hydrostatic ceiling
1476.38 psf

With the figures above, the maximum lateral formwork pressure comes to 1004 psf. Behind that figure, full hydrostatic ceiling is the biggest single quantity at 1476 psf; start there if the total looks wrong. 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.

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This result is a specification — 1,003.691 psf — 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

  • ACI 347R-14(21) Guide to Formwork for Concrete, Section 2.2.2, Eq. 2.4 (used across its full 0-15 ft/hr rate range as a single conservative envelope formula, since Eq. 2.3 and 2.4 are continuous and equal at R=7 ft/hr and Eq. 2.4 is always ≥ Eq. 2.3 below that): Pmax = Cw×Cc×[150 + 43400/T + 2800R/T] psf, with a floor of 600×Cw psf and a ceiling of full hydrostatic pressure (w×h). Cw (unit weight coefficient, Table 2.1) = 1.0 for 140-150 pcf concrete. Cc (chemistry coefficient, Table 2.2) = 1.0 for ordinary Type I/II/III cement with no retarder, rising to 1.2-1.4 for retarders or high slag/fly-ash content. This formula ONLY applies when slump ≤ 7 in, placement uses normal internal vibration to a depth ≤4ft, and R≤15 ft/hr — this is DISTINCT from this site's existing SCC formwork pressure calculator, which correctly uses full hydrostatic pressure (ACI 347R Eq. 2.1a) for self-consolidating concrete, since SCC and high-slump/retarded mixes fall outside this reduced formula's applicability and ACI 347R itself directs using full hydrostatic pressure for those cases.

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Frequently asked questions

Why is wall pressure lower than the full height of concrete suggests?
Because not all of it is still fluid. By the time the top of a wall is being placed, the concrete at the bottom has begun to set and is carrying its own weight rather than pushing outward. The pressure envelope rises with depth to a point and then stops — that point depends on how fast you are filling and how fast the mix stiffens.
What happens if the pour is faster than planned?
The pressure rises toward hydrostatic, and formwork designed for a slower rate can be overloaded. It is a genuine site risk rather than a theoretical one — a pour that is going well is tempting to accelerate, and the formwork design assumed a rate that nobody on the pour necessarily knows. The design rate belongs on the pour card.
Does temperature really matter that much?
It does. Concrete stiffens far more slowly at 5 °C than at 25 °C, so a winter pour keeps more of its height fluid and generates higher pressure at the same rate. Pressure formulas include temperature explicitly for this reason, and a summer design used unchanged in winter is not conservative.
Do ties and bracing resist the same thing?
No, and conflating them is a common error. Ties resist the concrete's lateral pressure pushing the two faces apart. Bracing resists everything else — wind on the face, the pour crew, placing equipment, and any accidental impact — and it keeps the form plumb and stable before and during the pour. A form can be adequately tied and still be blown over.