Engineering lab · Interactive tool
Bolt Preload + Torque Estimator
Use the T = KFd screening relationship to estimate installation torque or axial preload, then check tensile stress and arithmetic yield utilization.
Joint screening / T = KFd
Live calculationT = K · F · dBolt results updated. Axial preload 35 kilonewtons. Tensile stress 603.45 megapascals. Yield utilization 75.4 percent.
Model, assumptions, and a reproducible reference case
F = T/(Kd); σ = F/Aₜ
Reference inputs
Torque 70 N·m; nut factor K = 0.2; diameter 10 mm; tensile area 58 mm²; yield strength 800 MPa.
- Expected axial preload
- 35000 N
- Calculated by this tool
- 35000 N
The nut factor collapses friction effects into one uncertain coefficient. Joint separation, fatigue, installation scatter, and combined bolt stress require separate checks.
Check the material basis, load cases, and applicable design criteria before using a result. Warning thresholds are prompts for review, not acceptance criteria.
What the estimate can tell you
The calculation is useful for first-pass joint sizing and for exposing how assumptions about nominal diameter, tensile area, and nut factor affect the preload estimate.
Torque is only an indirect proxy for bolt tension. Friction at the threads and bearing surface consumes most of the applied torque, so a small change in condition can produce a large change in achieved preload.
Before specifying torque
- Establish a defensible nut-factor range for the actual finish and lubricant
- Include installation scatter and tool accuracy
- Check combined tensile and torsional stress
- Verify joint separation, slip, fatigue, and embedment
- Evaluate thread stripping and bearing-surface limits
- Correlate critical joints with direct preload measurement
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