Belt Drive Calculator

Formula

• Design power = Input power × Service factor
• Belt length and wrap angle from open-belt geometry
• Required belts = ceil(Design power ÷ Power per belt after correction factors)

About this calculator

Part of our Mechanical Calculators collection. Beams, bolts, springs, gears, bearings, and core ME calculations.

How it works

Pulley ratio includes slip allowance. Belt length and wrap angle use open-belt geometry. Power per belt and required belt count account for wrap and length correction factors. Status code flags when the selected section is under capacity.

Enter your values in the inputs above and click CALCULATE. Results appear on the right without a page reload. No login and no server upload.

Worked example

5 kW input, B-section belt, service factor 1.3, standard pulley layout.

1. Design power = 5 × 1.3 = 6.5 kW
2. Tool computes belt length, wrap angle, and power per belt from section data
3. Required belt count rounds up to the next whole belt

Result: Use the required belt count and check status: Safe, Caution, or Unsafe.

When to use

• First-pass V-belt drive sizing
• Checking if an extra belt is needed after load increase
• Estimating belt length for ordering

Limitations

• Screening values; confirm with manufacturer catalog at operating rpm
• Open belt geometry only
• Static power ratings simplified

FAQ

What does belt status mean?

Safe means pulley size, speed, and wrap angle are within typical limits. Caution or unsafe flags need a larger section or layout change.

Why add a service factor?

Real drives have shock, duty cycle, and load variation. Service factor adds margin above nominal motor power.

How is slip handled?

Slip percentage reduces driven pulley speed. Typical V-belt slip is 1 to 3% at steady load.