Bolt Load Calculator
Find how much tension, shear or combined load a bolt — or a group of bolts — can actually carry, with allowable capacity, a clear pass / fail against your applied load, and the minimum number of bolts you need.
How to Calculate Bolt Load Capacity
This bolt load calculator answers the question a torque value cannot: not how tight the bolt is, but how much load it can carry. It works out the tension and shear a fastener can take from its tensile stress area and tensile strength, divides by your factor of safety to get an allowable load, multiplies across the bolt group, and tells you plainly whether the connection passes — and the minimum number of bolts it would take if it does not.
Bolt Tension and Shear Strength
Tensile capacity uses the tensile stress area At (smaller than the shank, because of the threads) and the bolt’s ultimate strength Fu:
Shear strength is about 60% of tensile strength. Use the full shank area when the threads are excluded from the shear plane, and the reduced stress area when they are included. A bolt in double shear carries twice as much because two planes resist the load. The allowable load is the nominal capacity divided by the factor of safety (2.0 by default, matching the usual AISC value for bolts).
Worked example
Four 1/2-13 Grade 5 bolts (At = 0.1419 in², Fu = 120 ksi) in tension at a factor of safety of 2.0:
Rn = 120 × 0.1419 = 17,028 lb per bolt → allowable 8,514 lb each
Group of four = 34,056 lb. Against a 20,000 lb pull that is ~58% utilization — a comfortable PASS, and only 3 bolts are strictly required.
Combined Tension and Shear
When a bolt carries tension and shear at once, neither check alone is enough. The calculator uses the standard interaction:
A result under 1.0 passes; the further below, the more margin. This is the realistic case for bracket and hanger connections, where a load pulls and shears the bolts together.
How Many Bolts Do I Need?
Rather than guess, the bolt group calculator divides the total applied load by the allowable capacity of one bolt and rounds up, so you get the minimum bolt count directly. Increase the bolt size, step up the grade (Grade 5 to Grade 8, or Class 8.8 to 10.9), add bolts, or move threads out of the shear plane — each raises capacity in a predictable way.
Frequently Asked Questions
What is the difference between bolt torque and bolt load?
Torque is how hard you tighten a bolt to create clamp force; bolt load capacity is how much external tension or shear the bolt can resist before failing. This page handles capacity; pair it with the Bolt Torque Calculator for tightening.
Should threads be in or out of the shear plane?
Excluding threads from the shear plane uses the larger shank area and gives more shear capacity. Including them is the conservative, common assumption for shorter bolts.
What grade are most structural bolts?
SAE Grade 5 / metric Class 8.8 are the everyday workhorses; Grade 8 / Class 10.9 and 12.9 are high-strength. The calculator carries the tensile strength for each.
Does this include bearing on the plate?
Yes – the shear mode checks bearing on the connected material (2.4 Fu d t) and reports whichever limit, bolt shear or plate bearing, governs.
Related calculators
- Bolt Torque Calculator — the tightening side: torque, clamp load and preload.
- Factor of Safety Calculator — choose the right margin for the load case.
- Weld Strength Calculator — check the welds in the same connection.
- Stress Calculator — stress in the connected members.
- Steel Weight Calculator — weigh the members you are bolting.