How do I find center distance from a known belt length?

The center distance can be found by solving the belt length equation: C = [B + √(B² − 8(D2−D1)²)] / 8, where B = 2L − π(D1+D2). This is the inverse calculation.

What is the minimum wrap angle for belt drives?

The minimum recommended wrap angle on the smaller pulley is 120° for V-belts and 150° for flat belts. Below these values, belt slip increases significantly and power capacity drops.

How do I calculate belt speed?

Belt speed v = π × D × n / 60000, where D is pulley diameter in mm and n is speed in RPM. Result is in m/s. Maximum recommended belt speed is typically 25-30 m/s for standard V-belts.

What is the relationship between pulley diameters and speed ratio?

The speed ratio equals the inverse ratio of pulley diameters: n2/n1 = D1/D2. A larger driven pulley means speed reduction. This assumes no belt slip (typically 1-2% for V-belts).

Free Engineering Tool #087

Belt Drive Calculator

Calculate belt length from pulley diameters and center distance, or find center distance from a known belt length. Includes wrap angle, speed ratio, and belt speed.

Belt Length Center Distance Wrap Angle

Results

Belt Length

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Wrap Angle (small pulley)

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Speed Ratio

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Belt Speed

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Driven Speed

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Belt Length Formula

Center Distance from Belt Length

Wrap Angle

⚠️ Note: Minimum wrap angle on the small pulley should be ≥120° for V-belts. If below this, use an idler pulley or increase center distance.

Example

Given: D₁=100 mm, D₂=300 mm, C=500 mm

L = 2×500 + π(100+300)/2 + (300-100)²/(4×500)

L = 1000 + 628.3 + 20 = 1648.3 mm

Belt Drive Calculator | Belt Length & Center Distance | Free Online Tool

Published by admin on February 15, 2026 February 15, 2026

Results

Belt Length Formula

Center Distance from Belt Length

Wrap Angle