Anchor Bolt Pullout Capacity Calculator

How pullout resistance is calculated

Cast-in-place headed anchors rely on the bearing area beneath the head or nut to resist tension. ACI 318 expresses the nominal pullout strength N_pn as the product of concrete strength, projected bearing area, and an empirical coefficient. Using a circular head, the simplified relationship implemented by this calculator is shown below.

The design strength multiplies the nominal value by the strength reduction factor φ to cover variability and provide a safety margin: . Increasing embedment length linearly boosts pullout resistance, while higher concrete strength only increases capacity with the square root of f′_c, illustrating diminishing returns.

Example capacities

Typical values for 3⁄₄ in anchors embedded 6–10 in in normal-weight concrete illustrate the trend between concrete strength and embedment depth.

Remember that edge distance, spacing, and supplementary failure modes such as side-face blowout or concrete breakout may control the design rather than simple pullout. Always consult the governing building code and manufacturer guidance when anchoring critical equipment.