From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

Reinforced Concrete Beam Moment Capacity Calculator (ACI 318)

Estimate the nominal moment capacity of a singly-reinforced rectangular concrete beam.

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

Nominal moment capacity

176.65 kN·m

Check your inputs

This is the nominal (unfactored) moment capacity for a singly-reinforced rectangular section only — a real design also applies a strength reduction factor (φ, typically 0.9 for tension-controlled sections), checks minimum/maximum reinforcement ratios, and must be verified by a licensed structural engineer.

Stress block depth (a)
2.32 in

At the values currently entered, the nominal moment capacity works out to 177 kN·m. Note that tension steel area (as) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Confidence is moderate: the method is sound, but real materials and site conditions vary. 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 — 176.647 kN·m — 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 318 rectangular stress block method for a singly-reinforced beam: a = As x fy / (0.85 x f'c x b); Mn = As x fy x (d - a/2)

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.

Frequently asked questions

What is 'nominal' moment capacity?
It's the theoretical maximum moment the section can resist based purely on material properties and geometry — real designs multiply this by a strength reduction factor (φ, typically 0.9) to get the usable design capacity, and factored loads must stay below that reduced value.
Does this check for over-reinforcement?
No — a real design must verify the section is tension-controlled (steel yields before concrete crushes) per ACI 318's strain limits, which this simplified calculator doesn't check.
Does this apply to T-beams or doubly-reinforced sections?
No — this is for a singly-reinforced rectangular section only. T-beams and sections with compression steel need a different, more involved formula.