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?

Yes — that is what the anchor type selector is for. ACI 318 Chapter 17 gives kc = 17 for post-installed anchors against 24 for cast-in, and this calculator uses whichever you pick. Where a specific product has an ICC-ES evaluation report, use the kc that report qualifies: testing to ACI 355.2 or 355.4 can justify a value above 17, and the report's figure governs over the generic one.

Why is there no cracked or uncracked option?

Because cracking is not part of kc, which is the coefficient this calculator applies. ACI 318 handles it with a separate modification factor, Psi-c,N, further along the procedure — the basic strength shown here is already on a cracked-concrete basis, and an anchor verified to stay in uncracked concrete earns an increase this figure does not include. Treat what you see as the conservative starting point it is.

Materials & Quantities

Concrete Anchor Bolt Breakout Capacity Calculator (ACI 318)

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

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Anchor Embedment Depth (hef)

The effective embedment depth of the anchor into the concrete.

Measured from the concrete surface to the anchor's bearing surface (e.g. the underside of a headed bolt's head).

Concrete Compressive Strength (f'c)

The concrete's specified compressive strength.

Standard residential/commercial concrete is commonly 3,000-4,000 psi.

Anchor Type

Whether the anchor was cast into the wet concrete or drilled and fixed afterwards.

This is what kc distinguishes in ACI 318 Chapter 17 — 24 for cast-in, 17 for post-installed. It is NOT the cracked/uncracked question: cracking is handled separately by the modification factor Psi-c,N, which this basic figure does not include. Post-installed is the default because it is the lower coefficient, and because a qualified post-installed anchor's own ICC-ES evaluation report may permit a higher value than 17 — use that report's figure when you have it.

Basic breakout capacity

8.6 kips

Low confidence

This is the BASIC single-anchor breakout strength only (ANc/ANco = 1, no edge-distance, spacing or eccentricity reduction, and no Psi-c,N cracking modifier — ACI 318's basic equation is on a cracked-concrete basis, and an anchor verified to sit in uncracked concrete earns a further increase this figure does not take) — 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: 8,601.4 lb

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

ACI 318 Chapter 17 basic concrete breakout strength for a single anchor: Nb = kc x sqrt(f'c) x hef^1.5 (lb, psi, in), with kc = 24 for cast-in anchors and 17 for post-installed anchors
ACI 318 Chapter 17 treats concrete cracking separately, through the modification factor Psi-c,N applied to the basic strength — it is not part of kc

Inputs used

Anchor Embedment Depth (hef): 4 in
Concrete Compressive Strength (f'c): 4000 psi
Anchor Type: Post-installed anchor (kc = 17)

Intermediate steps

Equivalent in lbs: 8,601.4 lb

Final result8.6 kips

Confidence note: This is the BASIC single-anchor breakout strength only (ANc/ANco = 1, no edge-distance, spacing or eccentricity reduction, and no Psi-c,N cracking modifier — ACI 318's basic equation is on a cracked-concrete basis, and an anchor verified to sit in uncracked concrete earns a further increase this figure does not take) — 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.

What this calculation does not cover

This is a nominal strength, not a design capacity. No strength-reduction factor is applied and no factored load is checked against it, so the figure cannot stand as a code compliance check on its own.
Only concrete breakout in tension is modelled. Anchor steel fracture, pullout at the head, side-face blowout near a free edge, shear breakout and combined tension-plus-shear interaction are not calculated, and any one of them can govern the anchor instead.
The full unrestricted breakout cone is assumed. Member thickness, group behaviour where several anchors share a cone, and anchor reinforcement designed to carry the load past a breakout failure are all outside this calculation, on top of the edge-distance, spacing and eccentricity factors the result note already flags.
Normalweight concrete in ordinary service is assumed. There is no lightweight-concrete modification, no cracked-versus-uncracked modification, and no seismic provisions — an anchor in a seismic force-resisting system is subject to extra requirements this page does not touch.
For post-installed anchors the generic coefficient of 17 stands in for the actual product. It carries nothing about adhesive bond strength, elevated-temperature or sustained-load performance, hole cleaning, drilling method or installation torque, all of which the manufacturer's qualified evaluation report governs.

Add the equipment this sizes

This result is a specification — 8.6 kips — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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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 2026-09-03 · in the site-wide review of 2026-09-06 · v2.0.1

Regulatory standards & verification citations2

ACI 318 Chapter 17 basic concrete breakout strength for a single anchor: Nb = kc x sqrt(f'c) x hef^1.5 (lb, psi, in), with kc = 24 for cast-in anchors and 17 for post-installed anchors
ACI 318 Chapter 17 treats concrete cracking separately, through the modification factor Psi-c,N applied to the basic strength — it is not part of kc

Which documents these citations point at

Standards referenced: ACI 318 (American Concrete Institute, 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.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Anchoring Into Concrete and Masonryuses this calculator
Every concrete anchor drags a cone of substrate with it — edge distance, spacing and embedment are all arguments about that cone.
Bracing Formwork for the Pressure a Pour Actually Makesuses this calculator
A raker resists what would tip a wall form over, not the concrete's push on the sheathing — until the form loses its opposite face and the two become one load.
Setting Bollards and Concrete Barriersuses this calculator
Precast barrier is counted by the segment, a bollard is poured by the hole: how to price and book both before the trucks are ordered.

Called something else where you work? Anchor and fixing — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Cast-In Anchor Bolts vs Post-Installed Anchors — the factors that actually differ, with no invented prices.

How to calculate concrete anchor bolt breakout capacity (ACI 318) in 4 steps

Anchor Embedment Depth (hef)The effective embedment depth of the anchor into the concrete.
Concrete Compressive Strength (f'c)The concrete's specified compressive strength.
Anchor TypeWhether the anchor was cast into the wet concrete or drilled and fixed afterwards.
Basic breakout capacityThe tool computes the basic breakout capacity from those figures and shows the formula, its sources, and a confidence rating alongside it.

Basic breakout capacity by anchor embedment depth (hef)

Page defaults, not your figures above.

Anchor Embedment Depth (hef)	Basic breakout capacity (kips)
2 in	3.04
3 in	5.59
4 in	8.6
5 in	12
6 in	15.8
7 in	19.9

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?: Yes — that is what the anchor type selector is for. ACI 318 Chapter 17 gives kc = 17 for post-installed anchors against 24 for cast-in, and this calculator uses whichever you pick. Where a specific product has an ICC-ES evaluation report, use the kc that report qualifies: testing to ACI 355.2 or 355.4 can justify a value above 17, and the report's figure governs over the generic one.
Why is there no cracked or uncracked option?: Because cracking is not part of kc, which is the coefficient this calculator applies. ACI 318 handles it with a separate modification factor, Psi-c,N, further along the procedure — the basic strength shown here is already on a cracked-concrete basis, and an anchor verified to stay in uncracked concrete earns an increase this figure does not include. Treat what you see as the conservative starting point it is.

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.