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Concrete Anchor Bolt Breakout Capacity Calculator (ACI 318)

Estimate a single cast-in anchor's basic concrete breakout tension capacity, per ACI 318 Chapter 17.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Basic breakout capacity

54 kN

Low confidence

This is the BASIC single-anchor breakout strength only (ANc/ANco = 1, no edge-distance, spacing, or eccentricity reduction factors applied) — it assumes the anchor is far enough from any edge or other anchor to develop a full breakout cone. Real anchor design requires the complete ACI 318 Chapter 17 procedure, verified by a licensed engineer.

Equivalent in lbs
12143.15 lb

Running these inputs gives 54 kN as the basic breakout capacity. Low confidence on these inputs, so use the number to plan rather than to order. Currently reading for United States — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 54 kN — 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 — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

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.

Regulatory standards & verification citations

  • ACI 318 Chapter 17 basic concrete breakout strength for a single cast-in headed anchor: Nb = kc x sqrt(f'c) x hef^1.5 (lb, psi, in), with kc = 24 for uncracked concrete or 17 for cracked concrete

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Frequently asked questions

What does 'breakout capacity' mean?
It's the load at which a cone-shaped section of concrete breaks free around the anchor, rather than the anchor's steel yielding — for shallow embedment or weak concrete, breakout often governs over steel strength.
Why is the confidence rated 'low' even with a correct formula?
Because this calculator deliberately omits the edge-distance, anchor-spacing, and eccentricity reduction factors that real ACI 318 anchor design requires — those factors can reduce capacity substantially below this idealized 'anchor far from any edge' basic value.
Does this apply to post-installed (adhesive or expansion) anchors too?
The basic breakout formula's concept is similar, but post-installed anchors have their own manufacturer-specific ICC-ES evaluation report values that should be used instead of the generic cast-in anchor coefficients here.