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Calculate shaft key size, torque, stress, and safety instantly with our free online Shaft Key Calculator. Fast, accurate, and easy to use.
Designing a shaft key may seem like a small step in mechanical engineering, but it plays a big role in transmitting torque securely between a shaft and a hub. If the key fails, the entire system could stop working or even get damaged. That's why we’ve developed the Shaft Key Calculator, a powerful and user-friendly online tool designed to help engineers, technicians, and students calculate everything related to shaft keys with precision. Whether you're working on a new design or verifying an existing one, this calculator ensures safety and accuracy.
A shaft key is a small metal component inserted between a rotating machine element (like a gear or pulley) and the shaft. It locks the two together, ensuring the torque is transferred without slippage. Shaft keys are commonly made from steel and come in various shapes such as rectangular, square, or Woodruff types.
Using our shaft key calculator is simple and requires only a few inputs:
Step 1: Enter Shaft Dimensions
Input the shaft diameter, and choose your preferred unit (mm, inch, etc.).
Step 2: Input Torque
Add the torque you need to transmit. This can be in Newton-meters (Nm), foot-pounds (lb·ft), or other units.
Step 3: Enter Key Dimensions
Provide the width, height, and length of the key.
Step 4: Material Strength Values
Add the allowable shear stress and allowable bearing stress for the key material. If unknown, use default steel values.
Step 5: Shaft Strength and Stress Factor
Input the shaft’s allowable shear strength and the stress concentration factor (Kf), which accounts for weakening due to the keyway.
Step 6: Calculate
Click “Calculate” and get instant results.
The calculator uses accurate engineering formulas to compute stress and required key length:
Shear stress in the key is calculated using the formula:
τ = (2 × T) / (d × w × l)
Where:
Bearing stress between key and hub:
σ = (4 × T) / (d × h × l)
Where:
To make sure the shaft can handle the torque:
T_shaft = (π × d³ × τ_shaft) / (16 × Kf)
To ensure the key won't fail, calculate required length:
The longer of the two is the minimum safe key length.
Cutting a keyway weakens the shaft. We calculate that with:
e = 1 - 0.2(w/d) - 1.1(h/d)
This gives an idea of how much weaker the shaft becomes after keyway cutting.
Our Shaft Key Calculator is built to make your mechanical design process faster, safer, and more reliable. It’s ideal for calculating all the critical values you need when working with shaft keys whether you’re designing machinery, running safety checks, or learning how to calculate a shaft key for your project. With just a few inputs, you get complete safety analysis, material suggestions, and even improvement recommendations if the current design is unsafe.
The calculator supports both metric and imperial units, and it’s designed to meet real-world engineering needs.
A shaft key is used to lock a rotating machine element (like a gear or pulley) to a shaft, allowing torque transmission without slipping.
You calculate shaft key size using formulas based on torque, shaft diameter, and the key’s shear and bearing capacity. Our calculator automates this for you.
The weakening factor formula (e = 1 - 0.2(w/d) - 1.1(h/d)) estimates how much the keyway reduces shaft strength. The keyway should not exceed safe design limits.
The key length should be at least the larger of the shear or bearing length requirements. Our calculator shows you the minimum required key length.
No, you can use any material. Just enter its shear and bearing allowable stresses. Steel is just the default.