Design belt drives with quick engineering checks. Review length, wrap, speed, and allowance together instantly. Built for estimates, maintenance planning, fitting, procurement, and documentation.
Enter pulley diameters and center distance using the same unit. Add an allowance when you want fitting slack, splice margin, or procurement rounding.
Open belt length: L = 2C + π(D + d)/2 + (D - d)²/(4C)
Crossed belt length: L = 2C + π(D + d)/2 + (D + d)²/(4C)
Symbols: L is belt pitch length, C is center distance, D is the larger pulley diameter, and d is the smaller pulley diameter.
Wrap angle checks: the calculator also estimates pulley contact angles and arc contact lengths, which are useful for traction, grip, and drive performance reviews.
These equations are standard engineering approximations for preliminary design. Manufacturing corrections, groove geometry, belt thickness, and installation tension can be handled by adding allowance.
| Case | Belt Type | Driver Dia. (mm) | Driven Dia. (mm) | Center Distance (mm) | Approx. Belt Length (mm) |
|---|---|---|---|---|---|
| Example 1 | Open | 120 | 240 | 600 | 1771.49 |
| Example 2 | Crossed | 120 | 200 | 650 | 1842.04 |
| Example 3 | Open | 150 | 300 | 700 | 2114.89 |
These values are rounded examples for planning and checking. Real installed length can change with belt section, groove geometry, and fitting practice.
It estimates open or crossed belt pitch length from pulley diameters and center distance. It also reports wrap angles, arc contact lengths, straight spans, belt speed, and total material when multiple belts are required.
An open belt keeps both pulleys rotating in the same direction. A crossed belt reverses the driven pulley direction and usually increases wrap angle, but it also increases length and can raise belt twist and wear.
The center distance controls geometry and formula validity. If shafts are too close, the tangent construction becomes impossible and wrap calculations fail. That is why the calculator blocks invalid distance values.
Yes, when you want room for fitting, joining, take-up adjustment, procurement rounding, or installation practice. The base formula gives theoretical pitch length, while the allowance helps reflect your real purchasing or assembly target.
Yes. Choose the input unit first, then enter all dimensions in that same unit. The calculator converts internally and also returns the final belt length in several convenient unit formats.
Wrap angle shows how much of each pulley is in belt contact. Larger contact angle generally improves grip and power transfer. Very low wrap angles can increase slip risk, especially on smaller pulleys.
No. Belt speed is optional and appears only when driver RPM is entered. It helps with performance reviews, heat considerations, and comparing whether a proposed pulley combination stays within practical operating limits.
No. It is ideal for engineering estimates and quick checks, but final selection should still consider belt section, groove profile, service factor, allowable tension, environmental conditions, and manufacturer catalog recommendations.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.