Use this washer bearing pressure calculator to estimate the contact pressure under a washer, nut face or bolt head from bolt preload or clamp force. The calculator determines bearing area, bearing pressure, utilisation, factor of safety and required washer outer diameter.
This calculator checks the bearing pressure under a circular washer or bearing face. It uses the clamp force and annular bearing area to estimate the pressure applied to the clamped surface.
The calculator provides:
This calculator is useful for checking local bearing pressure under washers, bolt heads, nuts and clamped plates, especially when softer materials are used.
Annular bearing area:
Bearing pressure:
Design allowable bearing pressure:
Required outer bearing diameter:
Utilisation:
Factor of safety:
| Symbol | Description | Units |
|---|---|---|
| F | Clamp force or bolt preload | N |
| Di | Inner diameter / clearance hole diameter | mm |
| Do | Outer bearing diameter | mm |
| A | Annular bearing area | mm² |
| p | Bearing pressure | N/mm² |
| pallow | Allowable bearing pressure | N/mm² |
| SF | Safety factor | - |
| Case | Comment |
|---|---|
| Washer on steel plate | Often acceptable at relatively high bearing pressures, depending on material and surface condition. |
| Washer on aluminium | May require larger washers or lower preload to avoid local indentation. |
| Bolt head without washer | Bearing area may be smaller, increasing local pressure. |
| Soft gasket or plastic material | Allowable pressure may be much lower and should be checked carefully. |
Enter the clamp force and washer dimensions, then click calculate.
| Result | Meaning |
|---|---|
| Annular bearing area | The contact area between the washer or bearing face and the clamped surface. |
| Bearing pressure | The clamp force divided by the annular bearing area. |
| Design allowable pressure | The entered allowable bearing pressure divided by the safety factor. |
| Required outer diameter | The estimated outer bearing diameter needed to keep pressure within the design allowable value. |
| Utilisation | The calculated bearing pressure divided by the design allowable pressure. A value below 100% passes this simplified check. |
This calculator provides a simplified uniform bearing pressure check. It does not model local yielding, bending or non-uniform pressure distribution.
| This Calculator Includes | This Calculator Does Not Include |
|---|---|
| Annular washer bearing area | Non-uniform contact pressure |
| Bearing pressure from clamp force | Washer bending or cupping |
| Required outer diameter estimate | Surface roughness or coating effects |
| Utilisation and factor of safety | Embedment relaxation over time |
| Worked calculation | Detailed material crushing or indentation analysis |
For estimating clamp force from tightening torque, use the Bolt Preload Calculator.
For calculating tightening torque from target preload, use the Bolt Tightening Torque Calculator.
For checking bolt tensile stress, use the Bolt Tensile Stress Calculator.
Bearing pressure under a washer is calculated by dividing the clamp force by the washer contact area. For a flat circular washer, the contact area is normally treated as an annulus between the inner hole diameter and outer bearing diameter.
A larger washer outer diameter increases the bearing area and reduces the pressure on the clamped material. This can be important for softer materials such as aluminium, plastics, timber, composites or gasketed joints.
The selected allowable bearing pressure should be based on the weaker material in contact and the design requirement. For critical joints, local deformation, embedment loss and relaxation should also be considered.
For further fastener data, see the RoyMech reference pages: Bright Hexagon Screws, Nuts and Washers and Bolted Joint Design and Calculations.
For the full calculator section, see: Bolted Joint Calculators.
Bearing pressure is calculated by dividing the clamp force by the annular contact area under the washer:
For a circular washer, the bearing area can be estimated as:
A larger washer increases the bearing area and reduces local pressure on the clamped material. This can help reduce indentation, crushing or embedment.
No. This calculator assumes the washer or bearing face distributes load uniformly over the annular contact area.
Yes, but the allowable bearing pressure should be chosen carefully for the material. Soft materials may require much larger washers or reduced clamp force.
This calculator is intended for preliminary engineering calculations and educational use. Final design should consider washer stiffness, material data, surface condition, preload loss and relevant standards.