What is effective belt tension?

Effective tension (Te) is the net tangential force the belt exerts on the pulley to transmit power. It equals Power divided by Belt Speed: Te = P / v.

How is the tight-side tension T1 calculated?

Using the Euler-Eytelwein equation, the tension ratio is R = e^(µ·θ) for flat belts (or e^(µ·θ/sin(α)) for V-belts). Then T1 = Te·R / (R − 1) + Tc, where Tc is centrifugal tension.

What is centrifugal tension and when does it matter?

Centrifugal tension (Tc = m·v²) acts outward and reduces the effective grip of the belt on the pulley. At belt speeds above about 10 m/s it becomes significant and should not be ignored.

What coefficient of friction should I use?

Typical values: rubber belt on cast-iron pulley 0.30–0.35; rubber on steel 0.25–0.30; leather on cast iron 0.40–0.50. Always use the lower end of the range for design safety.

Why does V-belt use a groove angle correction?

The groove wedges the belt sideways, increasing the normal force and thus friction. The effective friction coefficient becomes µ_eff = µ / sin(α), where α is the half groove angle (typically 17°–20°).

What wrap angle should I use for the smaller pulley?

The smaller (driven) pulley always has the smaller wrap angle. For a two-pulley drive you can estimate it from the center distance and pulley diameters. Typical values are 150°–180°; below 120° the drive becomes unreliable.

Belt Tension Calculator

Name: Belt Tension Calculator
Availability: InStock
Author: Nham Vu

Enter power, belt speed, and friction data to instantly compute tight-side, slack-side, and effective tensions for flat or V-belt drives.

Drive Parameters

Belt Type

Flat Belt V-Belt

Transmitted Power

Belt Speed

Coefficient of Friction (µ) rubber/cast-iron ≈ 0.30

Wrap Angle on Smaller Pulley (°) typical 150°–180°

Belt Mass per Unit Length (kg/m) 0 = ignore centrifugal

Fill in the drive parameters and click Calculate

Summary

Enter power, belt speed, and friction data to instantly compute tight-side, slack-side, and effective tensions for flat or V-belt drives.

How it works

Enter the transmitted power (W or kW) and belt speed (m/s or ft/min).
Provide the coefficient of friction between belt and pulley (typically 0.3–0.5 for rubber on cast iron).
Enter the wrap angle on the smaller pulley (usually 150°–180°).
For V-belts, enter the groove half-angle (typically 17°–20°); the tool adjusts the friction factor automatically.
Optionally input belt mass per unit length to account for centrifugal tension.
Click Calculate to see effective tension, tight-side T1, slack-side T2, and the tension ratio.

Use cases

Sizing drive belts for motors, pumps, and fans in industrial machinery.
Verifying that an existing belt drive can transmit the required torque without slipping.
Comparing flat-belt and V-belt designs for the same power transmission requirement.
Estimating bearing loads from the sum of tight-side and slack-side tensions.
Selecting appropriate belt pre-tension during assembly and alignment.
Educational use in mechanical engineering courses on power transmission.
Checking belt safety factors against manufacturer rated tension limits.
Optimizing wrap angle and pulley diameter ratios for compact drive layouts.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu