What is the mechanical advantage of a screw?

Mechanical advantage (MA) is the ratio of output force to input force. For a screw, MA = circumference of effort arm / pitch. A screw with MA = 30 means 1 N of pushing force on the handle produces 30 N of linear clamping force (ignoring friction).

What is pitch in this context?

Pitch is the axial distance a screw travels in one complete 360° turn. For a metric M8 bolt with 1.25 mm thread pitch, the screw advances 1.25 mm per revolution.

What is the effort arm circumference?

It is the circle traced by the point where you apply force — typically the handle or wrench tip. Circumference = 2 × π × radius. A screwdriver with a 15 mm handle radius has a circumference of ≈ 94.2 mm.

Does friction affect the real mechanical advantage?

Yes. This calculator gives the ideal (theoretical) MA. Real screws have friction losses. The actual force output is lower; efficiency of 20–60% is common depending on thread angle and lubrication.

How does changing pitch affect MA?

A smaller (finer) pitch increases MA — you need more turns but generate more force. A larger (coarser) pitch decreases MA — faster travel but less force multiplication.

Can I use different units?

Yes. As long as pitch and circumference are in the same units (both mm, both inches, etc.) the ratio is dimensionless and correct. The output force section uses Newtons by default.

Screw Mechanical Advantage Calculator

Enter a screw's pitch and effort arm circumference to instantly calculate its mechanical advantage.

Screw Parameters

Units

Pitch (distance per revolution)

Effort Arm — enter as

Effort Arm Circumference (2 × π × radius)

Input Force (Effort) — optional

Mechanical Advantage

Fill in pitch and circumference, then click Calculate.

Common Screw Examples

Screw Type	Pitch (mm)	Handle ⌀ (mm)	MA

Summary

A screw is a simple machine that converts rotational effort into linear force. Its mechanical advantage (MA) equals the circumference of the effort arm divided by the pitch — the distance the screw advances per full turn. A higher MA means less force is needed to drive the screw, but more turns are required. This calculator lets you compare screws side-by-side and explore how pitch and handle radius affect force multiplication.

How it works

Enter the pitch of the screw (distance advanced per one full revolution).
Enter the circumference of the effort arm (2 × π × handle radius), or provide the radius directly.
The calculator divides circumference by pitch to compute the mechanical advantage.
Optionally enter the input force (effort) to see the output force the screw can produce.
Review the worked formula and adjust inputs to compare different screw designs.

Use cases

Physics students solving simple-machine problems on screws.
Engineers comparing screw designs for press, clamp, or jack applications.
Hobbyists sizing a lead screw for a CNC machine or linear actuator.
Teachers demonstrating how pitch and handle length trade speed for force.
DIY builders selecting the right bolt or wood screw for a clamping fixture.
Checking whether a proposed screw press can generate a required load.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu