Free V-Belt Drive Sizing Calculator

Calculate pulley speed ratio, driven shaft RPM, exact belt pitch length, and center-to-center distance for industrial A, B, and V-belts.

⚙️ Pulley Sizes & Motor Speed

Standard V-Belt Section Profile

Motor / Driver RPM Standard 4-pole motor

Driver Pulley Dia (In)

Driven Pulley Dia (In)

Desired Center Dist (In)

📊 Speed Ratio & Belt Sizing

Driven Shaft Output Speed

875 RPM

2.00 : 1 Speed Reduction (2× Output Torque)

Calculated Belt Length

52.7 Inches

Use Standard A51 or A52

Small Pulley Arc of Contact

168.9° (Safe)

Arc factor C_theta = 0.98

Belt Linear Speed: 1,604 ft/min (Optimal: 1,000–5,000)

Actual Center with Standard Belt: 17.6 inches

Minimum Sheave Diameter Check: Passed (3.5" > 3.0" min)

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Understanding V-Belt Mechanical Drives

V-belts transmit mechanical power through the wedging action of their trapezoidal cross-section inside the pulley sheave groove. This wedging multiplies normal friction force, enabling V-belts to transmit far higher torque than flat belts with significantly lower tension.

V-Belt Design Formulas

RPM_{\text{driven}} = RPM_{\text{driver}} \times \frac{d_{\text{driver}}}{D_{\text{driven}}}

L = 2C + 1.57(D + d) + \frac{(D - d)^2}{4C} \quad \text{(Pitch Length in inches)}

V = \frac{\pi \cdot d \cdot RPM}{12} \quad \text{(Belt Speed in Feet Per Minute)}

\theta = 180^\circ - 2 \arcsin\left(\frac{D - d}{2C}\right) \quad \text{(Contact Arc in degrees)}

The Minimum Sheave Diameter Rule

Running a heavy V-belt around an undersized pulley forces the synthetic cords through severe repetitive bending flex, generating internal frictional heat and causing premature cord separation. Always adhere to minimum manufacturer diameters: 3.0" for A-section, 5.4" for B-section, and 9.0" for C-section.

Frequently Asked Questions

What is the difference between an A-section and B-section V-belt?

A-section belts measure 1/2" (13mm) across the top width and 5/16" (8mm) in height, rated for 1 to 5 HP per strand. B-section belts measure 21/32" (17mm) wide and 13/32" (11mm) thick, rated for 3 to 15 HP per strand.

Why does belt speed matter?

Optimal V-belt efficiency occurs between 1,000 and 5,000 feet per minute (FPM). Above 5,000 FPM, centrifugal force throws the belt outward, reducing wedging contact friction and requiring dynamically balanced cast-iron sheaves.

How do standard belt trade numbers work (e.g. A50)?

For classical belts, the number after the letter designates inside circumference in inches (e.g. A50 = 50.0" inside length). Pitch length is approximately inside length + 1.3" for A-section, or + 1.8" for B-section.