Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!


Pulleys, blocks and tackles.

A pulley is a device that can increase the magnitude of an effort force .

Without Pulley

Dulley - force without pulley

With no pulley - the effort force is similar to the load - in opposite direction.

S = F                                  (1)


S = effort force (N, lb)

F = load (N, lb)

Single Pulley

Fixed Pulley

Pulley - force with single fixed pulley

With a single fixed pulley the effort force is similar (or more due to efficiency loss) to the load.

S = F                                (2)

The advantage with the single fixed pulley is that the direction of force is changed - it is possible to pull down instead of lifting up.

Movable Pulley

Pulley - force with single movable pulley

With a single moveable pulley the effort force is half (or more due to efficiency loss) of the load.

S = 1/2 F                                (3)

Combined Pulleys

Pulley - force with combined pulley

With a combined moveable pulley as above - the effort force is half (or more due to efficiency loss) of the load.

S = 1/2 F                               (4)

Pulley - force with  combined pulley

With two pulleys and the ropes as above - the effort force is 1/3 (or more due to efficiency) of the load.

S = 1/3 F                             (5)

General Equation for Blocks and Tackles

The general effort force equation for a block or tackle to raise or pull a load can be expressed as

S = F / (μ n)

= (m g) / (μ n)                                (6)


S = effort force (N, lb)

F = load (often weight ) (N, lb)

m = mass (kg, slugs ) (when lifting a mass)

g = constant of gravitation (9.81 m/s2, 32.17405 ft/s2) (when lifting a mass)

μ = mechanical efficiency of the system (equal to one for an ideal friction-less system, a fraction less than one for real-world systems with energy losses due to friction)

n = number of ropes between the sets of pulleys

Block, Tackle or Pulley Calculator

The calculator below can be used to calculate effort force in block, tackle or pulley construction. The calculator can be used for metric and imperial units as long as the use of units are consistent.

Note that kg is the SI units for mass - more about mass and weight !

Example - Pulley and Effort Force

Pulley example - force with 4 ropes

The effort force for a pulley with 4 ropes , friction loss μ = 0.8, and load 100 kg can be calculated as

S = (100 kg) (9.81 m/s2) / ((0.8) (4))

= 307 N

Related Topics

  • Dynamics

    Motion of bodies and the action of forces in producing or changing their motion - velocity and acceleration, forces and torque.
  • Mechanics

    The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more.

Related Documents


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2007). Pulleys. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter