👤 By whycalculator Team 📅 Last Updated February 24, 2026
Belt Length (2 Pulleys)
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This Belt Length Calculator for 2 Pulleys is designed to make mechanical calculations simple and stress-free. Whether you’re working on a workshop project, designing a machine system, or just double-checking measurements, this tool helps you quickly determine the exact belt length required. Instead of manually solving formulas every time, you can enter pulley diameters and center distance and get instant, accurate results.
How to Calculate Belt Length for 2 Pulleys
To calculate the belt length between two pulleys, you need three values: Large Pulley Diameter (D), Small Pulley Diameter (d), and Center Distance (C) between the pulley shafts.
Open Belt Drive Formula
Standard Formula:
L = 2C + (π (D + d) / 2) + ((D − d)² / 4C)
Where:
- L = Belt Length
- C = Center Distance
- D = Diameter of Larger Pulley
- d = Diameter of Smaller Pulley
- π ≈ 3.1416
Step-by-Step Example (Open Belt)
Suppose:
- D = 200 mm
- d = 100 mm
- C = 500 mm
Step 1: Apply formula
L = 2(500) + (3.1416 × (200 + 100) / 2) + ((200 − 100)² / (4 × 500))
Step 2: Solve
L = 1000 + 471.24 + 5
L = 1476.24 mm
Final Belt Length ≈ 1476 mm
Cross Belt Drive Formula
For a cross belt system, the formula changes slightly:
L = 2C + (π (D + d) / 2) + ((D + d)² / 4C)
Notice the difference: instead of (D − d)², we use (D + d)².
Important Notes
- Make sure all units are the same before calculating.
- The formula assumes pulleys are aligned properly.
- This calculation works for standard open and cross belt drives.
Belt Length Reference Table (Open Belt Drive)
| Large Pulley (D) | Small Pulley (d) | Center Distance (C) | Approx. Belt Length (L) |
|---|---|---|---|
| 200 mm | 100 mm | 500 mm | 1476 mm |
| 150 mm | 100 mm | 400 mm | 1179 mm |
| 300 mm | 150 mm | 600 mm | 1973 mm |
| 250 mm | 120 mm | 550 mm | 1718 mm |
| 180 mm | 90 mm | 450 mm | 1347 mm |
| 100 mm | 100 mm | 300 mm | 942 mm |
| 220 mm | 110 mm | 480 mm | 1506 mm |
| 350 mm | 200 mm | 700 mm | 2334 mm |
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