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Calcimator

Keyway Design Calculator

Design shaft keyways by calculating shear and compressive stresses in the key. Determine minimum key length and safety factor.

Inputs

in
in·lb
in
in
in
psi

Results

Minimum Key Length

1.11 in

Safety Factor

1.8

Shear Stress5,000 psi
Compressive Stress10,000 psi
Force on Key5,000 lb
How to Use This Calculator
  1. Enter the Shaft Diameter in inches — ANSI B17.1 standard key sizes are based on shaft diameter.
  2. Enter the Transmitted Torque in in·lb — compute as T = 63,025 × HP / RPM if starting from power.
  3. Enter the Key Width (w) and Key Height (h) in inches — for square keys w = h; use ANSI B17.1 tables for standard sizes.
  4. Enter the Active Key Length (L) — the engaged portion should be at least 1 to 1.5 times the shaft diameter.
  5. Enter the Key Yield Strength in psi: standard 1018 steel key stock ≈ 36,000 psi.
  6. Review the Minimum Key Length required for shear and bearing, the Shear and Compressive Stresses, and the Safety Factor — values below 2.0 warrant a larger key or stronger material.

How the result changes with Shaft Diameter

Shaft DiameterMinimum Key LengthSafety Factor
2.231 in2.01
7.160.31 in6.44
130.17 in11.7
180.12 in16.2

What each input means

Shaft Diameter
Diameter of the shaft at the keyway location. Key size is typically standardized based on shaft diameter.
Transmitted Torque
Torque transmitted through the keyed connection. T = 63,025 × HP / RPM.
Key Width (w)
Width of the square or rectangular key. Standard: 1/4 shaft diameter (ANSI B17.1).
Key Height (h)
Height (thickness) of the key. Square keys have h = w; flat keys have h < w.
Key Length (L)
Active engaged length of the key. Should be at least 1× to 1.5× the shaft diameter.
Key Yield Strength
Yield strength of the key material. Standard key stock (1018 steel) ≈ 36,000 psi.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Shaft Diameter = 2, Transmitted Torque = 5000, Key Width (w) = 0.5, Key Height (h) = 0.5 = 6 input(s) provided
  2. Calculate Minimum Key Length
    Minimum Key Length
    1.111 = 1.111
  3. Calculate Safety Factor
    Safety Factor
    1.8 = 1.8
  4. Calculate Shear Stress
    Shear Stress
    5000 = 5000
  5. Calculate Compressive Stress
    Compressive Stress
    10000 = 10000

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