Bolt Shear Calculator
Calculate the shear and tension capacity of a bolt from its diameter and allowable stress values, for connection design checks.
How this calculator works
A bolt resists load across its circular cross-section. This calculator finds that cross-sectional area from the bolt’s diameter, then multiplies by the allowable stress values for shear and tension to find how much load the bolt can carry in each mode. For shear, it also accounts for whether the bolt crosses one shear plane (single shear) or two (double shear).
Formula: Bolt cross-section area = π × (diameter ÷ 2)². Shear capacity = area × allowable shear stress × number of shear planes (1 for single shear, 2 for double shear). Tension capacity = area × allowable tension stress.
Worked example
A 0.75-inch diameter bolt (A325 structural bolt), allowable shear stress 21,000 psi, allowable tension stress 29,000 psi, single shear:
- Area ≈ 0.442 in²
- Shear capacity ≈ 9,278 lb
- Tension capacity ≈ 12,812 lb
Notes
Double shear — where the bolt crosses two shear planes, as in a lap joint with a member sandwiched between two plates — roughly doubles the shear capacity compared to single shear for the same bolt diameter and allowable stress.
A325 and A490 are the two most common structural bolt grades, with A490 rated for meaningfully higher allowable stresses than A325. Always use the allowable stress values that match your bolt’s actual grade rather than a generic assumption, since using the wrong grade’s values will misstate the bolt’s real capacity.
How to use
Enter the bolt diameter, the allowable shear and tension stress values for your bolt grade, and whether the connection puts the bolt in single or double shear. The calculator returns both the shear capacity and the tension capacity in pounds.
This is a planning estimate using standard AISC/AWS engineering formulas, not a substitute for engineering design. Confirm actual weld and connection sizing with a licensed structural engineer.
Frequently asked questions
What's the difference between single shear and double shear?
Single shear is when the bolt crosses one plane between connected parts, like a bolt joining two overlapping plates. Double shear is when the bolt crosses two planes, such as a lap joint where a middle member is sandwiched between two outer plates. Double shear roughly doubles the bolt's shear capacity for the same diameter.
What's the difference between A325 and A490 bolts?
A325 and A490 are the two most common structural bolt grades. A490 is a higher-strength bolt rated for meaningfully higher allowable shear and tension stresses than A325. Always use the allowable stress values published for your bolt's actual grade rather than assuming one generic value.
Why does the formula use the bolt's cross-sectional area?
A bolt resists shear and tension across its circular cross-section, so capacity depends on that area, not the diameter alone. The area is calculated as π times the radius squared (half the diameter, squared), which is why doubling the diameter more than doubles the capacity.
Should I check shear capacity, tension capacity, or both?
It depends on how the connection loads the bolt. A bolt loaded parallel to the connected surfaces (like a lap joint) is primarily in shear. A bolt loaded perpendicular to the surfaces (like a hanging bracket pulling straight out) is primarily in tension. Many real connections combine both and need a combined check.
Estimates only. Verify quantities with your supplier before purchasing.