SettingsSettings for this calculationUS
The column's total cross-sectional area.
For a 400 x 400 mm square column, Ag = 160,000 mm² — about 248 in².
The total cross-sectional area of longitudinal rebar.
Sum the area of every longitudinal bar in the column.
The concrete's specified compressive strength.
The SPECIFIED strength the concrete was designed to, not a cube or cylinder result from the pour — design uses the specified value and a test result is a check on whether it was met. Where an existing structure is being assessed and the specification is unknown, that is a testing problem rather than a number to estimate: column capacity scales with this directly, and a guess propagates straight into the answer.
The rebar's yield strength.
420 MPa (Grade 60) is standard US construction rebar.
Maximum nominal axial capacity
970 kips
This is the maximum NOMINAL capacity (already including the 0.80 tied-column reduction for accidental eccentricity) — a design must still apply the strength reduction factor (φ, typically 0.65 for tied columns) and verify slenderness effects, both outside this calculator's scope.
- Reinforcement ratio
- 2.5 %
They open the calculator with your figures already in it
Reinforced Concrete Tied Column Axial Capacity Calculator (ACI 318): 970 kips — 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)
- ACI 318 maximum nominal axial capacity for tied columns: Pn(max) = 0.80 x [0.85 x f'c x (Ag - Ast) + fy x Ast]
Inputs used
- Gross Column Area (Ag)
- 248 in²
- Longitudinal Steel Area (Ast)
- 6.2 in²
- Concrete Strength (f'c)
- 4061.06 psi
- Steel Yield Strength (fy)
- 60915.85 psi
Intermediate steps
- Reinforcement ratio
- 2.5 %
Confidence note: This is the maximum NOMINAL capacity (already including the 0.80 tied-column reduction for accidental eccentricity) — a design must still apply the strength reduction factor (φ, typically 0.65 for tied columns) and verify slenderness effects, both outside this calculator's scope.
What this calculation does not cover
- Nominal, not factored. Nothing here has been through the strength reduction factor (the confidence note names it: φ, typically 0.65 for a tied column), and nothing has been compared against a factored load. This is a capacity figure, not a check that the column is adequate, and it is not a design.
- Axial load only. This is one point on the top of the P-M interaction diagram, not the curve. Real columns also carry moment — frame action, an eccentric beam reaction, wind or seismic drift — and any bending pulls usable axial capacity below this number, often steeply.
- Short-column value. Slenderness is not considered at all: unbraced length, end restraint and sway frames sit outside it, and a slender column needs a separate moment magnification check that can cut capacity well below what is shown here.
- No detailing is checked. Tie size and spacing, minimum bar count, clear cover, bar spacing, lap-splice congestion, and whether the steel area you entered physically fits in the section all go unverified — the calculation sees two areas and two strengths and nothing about how the bars are arranged. Seismic confinement requirements are outside it entirely.
- It assumes the column is built as entered and the concrete reaches its specified strength. Fire resistance, exposure and durability, creep and shrinkage under sustained load, loading applied to young concrete during construction, and the footing under the column are all outside the calculation.
Add the equipment this sizes
This result is a specification — 970 kips — 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 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- ACI 318 maximum nominal axial capacity for tied columns: Pn(max) = 0.80 x [0.85 x f'c x (Ag - Ast) + fy x Ast]
Which documents these citations point at
Standards referenced: ACI 318 (American Concrete Institute, United States).
Cite this page
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