Screw Jack Force Calculator

Estimate the input force, torque, or effort required to lift or lower a load using a mechanical screw jack system.

Load Parameters
Screw Parameters
Friction & Efficiency
Handle Parameters
Calculation Options

  1. Enter the load value to be lifted/lowered
  2. Input screw parameters: pitch, mean diameter, and thread type
  3. Set friction parameters (either efficiency or coefficient)
  4. Enter handle length/radius
  5. Choose desired output: Torque, Force, or Mechanical Advantage
  6. See the real-time result and optional graph

Torque Required to Lift Load

T = (W × dₘ)/2 × (l + πμdₘ)/(πdₘ - μl)

Where:

  • W = Load (N)
  • dₘ = Mean diameter of screw (m)
  • l = Lead = pitch × number of starts
  • μ = Friction coefficient
Effort Force on Handle

F = T / r

Where r is handle length (m)

Mechanical Advantage

MA = W / F

Parameter Value
Load 10,000 N
Pitch 5 mm
Mean Diameter 40 mm
Handle Length 0.25 m
Efficiency 30%
Output Force ~133.3 N
Torque ~33.3 Nm

Thread Type Typical Efficiency
Square Thread 30–40%
Acme/Trapezoidal 25–35%
Ball Screw 85–95% (not self-locking)
Input Force (F)

0

N
Torque (T)

0

Nm
Mechanical Advantage

0

Efficiency

0

%
Formulas

Torque (T): T = (W × dₘ)/2 × (l + πμdₘ)/(πdₘ - μl)

Input Force (F): F = T / r

Mechanical Advantage (MA): MA = W / F

Efficiency (η): η = (W × l) / (2π × T)

Practical Tips
  • Screw jacks are typically self-locking when the friction angle is greater than the lead angle.
  • Higher efficiency means less effort required but may reduce self-locking capability.
  • Square threads are more efficient but harder to manufacture than trapezoidal threads.
  • For lifting heavy loads, consider using multiple-start threads to reduce required torque.
Performance Graphs