Bolt Clamping Force Calculator — Torque to Tension with K-Factor Analysis
Calculate Clamping Force from Applied Torque with Yield and Proof Load Warnings
Free bolt clamping force calculator for mechanical engineers and millwrights. Enter bolt size, grade, applied torque, and lubrication condition to calculate clamping force using F = T / (K × d). Covers 10 inch sizes and 10 metric sizes with 5 inch grades and 4 metric property classes.
\nIncludes real-time warnings when torque approaches proof load or yield strength. Visual status bars show percentage of proof load and yield, color-coded green through red. Five-level warning system from Notice through Critical alerts you before you stretch or break the bolt.
Look up recommended bolt torque values by grade
Bolt Torque Calculator →Get clearance and counterbore dimensions for your bolts
Counterbore & Clearance Calculator →Calculate tap drill sizes for threaded holes
Tap Drill Calculator →Reference torque-tension relationships
Torque-Tension Calculator →How It Works
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Select Bolt Size and System
Choose Inch or Metric, then select the bolt diameter from 10 standard sizes in each system.
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Select Bolt Grade
Choose SAE Grade 2, 5, 8, ASTM A325, A490, or Metric 8.8, 10.9, 12.9, A4-70 stainless.
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Choose Lubrication
Select K-factor preset: Dry (0.20), Zinc (0.18), Oiled (0.15), Anti-Seize (0.12), or Moly (0.10). Or enter a custom K-factor.
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Enter Applied Torque
Enter torque in ft-lbs or N-m. The calculator displays resulting clamping force in pounds and kilonewtons.
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Review Safety Margins
Check the visual status bars for proof load and yield percentage. Green is safe, yellow is caution, red is too close to bolt limits.
Built For
- Millwrights torquing flange bolts and verifying proof load limits
- Mechanical engineers calculating required torque for target clamping force
- Maintenance technicians verifying torque specifications match installed bolt grade
- Structural steel erectors checking A325 and A490 bolt preload requirements
- Machine builders specifying torque values for assembly work instructions
- Quality engineers auditing bolt torque against bolt grade capabilities
Features & Capabilities
K-Factor Presets
Five built-in lubrication presets plus custom entry. K-factor is the dominant variable in torque-tension and the most common source of assembly errors.
Visual Status Meters
Color-coded bars showing % of proof load and % of yield. Green (under 75%), yellow (75-90%), red (over 90%).
Five-Level Warning System
NOTICE through CRITICAL warnings trigger automatically based on inputs.
Bolt Grade Database
Complete proof load and yield data for SAE Grades 2/5/8, ASTM A325/A490, and Metric 8.8/10.9/12.9/A4-70.
Unit Conversion
Enter torque in ft-lbs or N-m, view force in pounds or kilonewtons. Real-time conversion.
PDF Export
Export analysis as a branded PDF for maintenance work orders or assembly documentation.
Frequently Asked Questions
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