Anchor Bolt Pullout Estimator
Estimate an anchor bolt's tensile capacity by comparing ACI 318 concrete breakout strength against the bolt's own steel tensile strength, reporting whichever governs plus an allowable working load at your chosen safety factor. Runs entirely in your browser.
Input
Sets the concrete-breakout kc constant — cast-in anchors get a higher kc than post-installed.
Typical: 20-40 MPa (roughly C20/25 to C32/40).
Applied to the governing ultimate capacity to get an allowable working load — 4 is a common conservative screening value; a real design uses ACI 318's own φ-factors instead.
Output
| Item | Value |
|---|---|
| No data yet | |
Guides
Estimate an anchor bolt's tensile capacity by checking two failure modes against each other — concrete breakout and the bolt's own steel tensile strength — and reporting whichever one governs, plus an allowable working load at a safety factor you choose.
Most quick versions of this calculator hide the formula behind a single "empirical coefficient" you have to already know. This one runs the actual ACI 318 concrete breakout equation and compares it against the bolt's steel strength, so you can see which failure mode is limiting the connection — not just a single opaque number.
How to use it
- Pick the anchor type — cast-in headed anchor or post-installed (mechanical/adhesive). This sets the concrete-breakout kc constant; cast-in anchors get a higher one.
- Enter the anchor diameter and effective embedment depth, both in mm.
- Enter the concrete's compressive strength (f'c, in MPa) — typically 20-40 MPa for ordinary structural concrete.
- Pick the bolt grade (4.6 through 10.9), or choose Custom to enter your own ultimate tensile strength.
- Set the overall safety factor — 4 is a common conservative screening value.
- Read the governing ultimate capacity (whichever of concrete breakout or steel tension is lower) and the allowable working load, in both kN and lbf.
The formulas
Concrete breakout — ACI 318-19 §17.6.2.2.1's basic single-anchor breakout strength, SI form:
Nb = kc × √f'c × hef^1.5
kc = 10 for cast-in headed anchors, 7 for post-installed anchors (the SI-native constants ACI 318-19 publishes alongside the US customary kc = 24 / 17). This is the basic breakout strength — it assumes the anchor is far enough from edges and other anchors that group and edge-distance effects don't reduce it.
Steel tensile strength — the bolt's own stress area times its ultimate tensile strength:
Nsa = Ase × futa
Ase is approximated as 75% of the nominal (major-diameter) cross-section — a standard rule of thumb for a threaded fastener's reduced tensile stress area absent a specific thread spec.
The tool reports min(Nb, Nsa) as the governing capacity, since either failure mode can control depending on the anchor's proportions and the concrete strength.
What this doesn't cover
This is a screening estimate, not a full ACI 318 Appendix D design. It deliberately doesn't apply edge-distance, spacing/group, eccentricity, or cracked-concrete modification factors — all of which need the anchor's actual layout (edge distances, spacing to neighboring anchors, applied moment) to compute. It also doesn't check installation-specific ICC-ES data for a particular post-installed anchor product, which can differ meaningfully from the generic kc figure used here.
Is this a substitute for a structural engineer?
No. This applies standard textbook formulas from the dimensions and material properties you supply. A real anchor design — especially anything load-bearing, seismic, or safety-critical — needs the full ACI 318 Chapter 17 / Appendix D (or CCD method) check, and a qualified structural engineer's review.
Related tools
For the bolt's installation torque rather than its pullout capacity, see the Bolt Torque Calculator. Sizing a weld instead of a bolted connection? Try the related weld-sizing tools in the mechanical-manufacturing category.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/anchor-bolt-pullout-estimator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"anchorType": "cast-in",
"anchorDiameter": "16",
"embedmentDepth": "100",
"concreteStrength": "25",
"boltGrade": "8.8",
"safetyFactor": "4"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `anchor-bolt-pullout-estimator` tool (Anchor Bolt Pullout Estimator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.