Pulley Force Calculator

Calculator

System mode

Choose the scenario you want to model.

Pulley configuration

For tackle, set supporting strands below.

Supporting strands (n)

Used when “Block and tackle” is selected.

Load mass (m₁)

kg. Also acts as Mass 1 in two-mass mode.

Counter mass (m₂)

kg. Used only in two-mass mode.

Gravity (g)

m/s². Earth standard is 9.81.

Target acceleration (a)

m/s². Use 0 for constant-speed lift.

Efficiency

% accounts for bearing and rope losses.

Rope pull angle (θ)

degrees from vertical. 0° means straight up.

Include moving rope mass?

Adds rope mass to the moving load in lift mode.

Moving rope mass

kg. Only used if rope mass is enabled.

Notes (optional)

Saved with your result exports.

Example data table

Scenario	Load (kg)	Mode	MA	Efficiency (%)	Angle (deg)	Acceleration (m/s²)	Estimated effort
Workshop lift	50	Lift	4	90	0	0	~136 N
Short angled pull	50	Lift	4	85	20	0	~165 N
Two-mass demo	50 vs 30	Atwood	1	95	0	—	Acceleration computed

Numbers are illustrative and depend on chosen assumptions.

Formulas used

Lift / Hoist

Models the force needed to raise a load.

F_load = m_total (g + a)
F_effort ≈ F_load / (MA · η · cos(θ))
T_strand ≈ F_load / MA

Atwood / Two-mass (approx.)

Shows ideal and adjusted acceleration estimates.

a₀ = (m_H − m_L)g / (m_H + m_L)
a ≈ (m_H − m_L)g · η · cos(θ) / ((m_H + m_L) · MA)
T_H ≈ m_H (g − a), T_L ≈ m_L (g + a)

Notes: η is efficiency (0–1). Angle θ is measured from vertical. These are engineering approximations and do not replace a certified lifting plan.

How to use this calculator

Select a mode: single-load lifting or two-mass motion.
Pick the pulley configuration and set supporting strands if needed.
Enter masses, gravity, and your target acceleration if lifting.
Add efficiency and pulling angle to match real conditions.
Click Calculate. Download CSV or PDF if required.

FAQs

1) What is mechanical advantage in a pulley?

Mechanical advantage is the load support factor from rope strands. More supporting strands reduce effort, but increase rope travel. Real systems lose some benefit due to friction.

2) Why does efficiency matter so much?

Bearings, sheave friction, rope bending, and misalignment waste force. A 90% efficient system needs about 11% more effort than ideal. Lower efficiencies raise effort quickly.

3) What does the rope pull angle change?

If you pull off-vertical, only the vertical component lifts the load. The calculator divides by cos(θ). At 30°, you need about 15% more force.

4) How many supporting strands should I enter?

Count the rope segments directly supporting the moving block. Do not count the free end you pull unless it supports the moving block. For simple tackle, it equals the theoretical MA.

5) Can I use this for constant-speed lifting?

Yes. Set acceleration to 0 m/s². The result becomes the steady lifting effort, adjusted for mechanical advantage, efficiency, and pull angle.

6) How accurate is the two-mass mode?

It gives a practical estimate. Real setups also depend on pulley inertia, rope stretch, and friction models. Use measured efficiency and keep angles realistic for best results.

7) Is this suitable for safety-critical rigging?

No. Use it for learning, planning, and quick checks. For lifting people or critical loads, follow local standards and a qualified engineer’s rigging plan.