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Calcimator

Belt Drive Design Calculator

Design V-belt or flat belt drives. Calculate belt length, speed ratio, belt speed, and tight/slack side tensions for power transmission.

Inputs

in
in
in
RPM
HP

Results

Speed Ratio

2:1

Belt Length

76.65 in

≈ 13 smartphones

Belt Speed2,749 ft/min
Tight Side Tension94.3 lb
Slack Side Tension34.3 lb
How to Use This Calculator
  1. Enter the Driver Pulley Diameter in inches — use the pitch diameter for V-belts, not the outside diameter.
  2. Enter the Driven Pulley Diameter. A larger driven pulley reduces output speed and increases torque (speed reduction).
  3. Set the Center Distance between shaft centerlines in inches. Aim for 1–2× the sum of the pulley diameters for good wrap angle.
  4. Enter the Motor Speed in RPM and the Transmitted Horsepower for the application.
  5. Review the Speed Ratio and Belt Length — use the belt length to order the correct standard V-belt designation.
  6. Check Tight Side and Slack Side Tensions to verify the shaft bearings and belt are rated for those loads.

How the result changes with Driver Pulley Diameter

Driver Pulley DiameterSpeed RatioBelt Length
6.91.74:177.96 in
220.55:1102.45 in
390.31:1135.7 in
540.22:1170.05 in

What each input means

Driver Pulley Diameter
Effective diameter of the driving (motor) pulley. For V-belts, use the pitch diameter.
Driven Pulley Diameter
Effective diameter of the driven (load) pulley. Larger gives more speed reduction.
Center Distance
Distance between pulley shaft centers. Should be 1-2× the sum of pulley diameters for good wrap angle.
Motor Speed
Speed of the driver pulley (motor). Common motor speeds: 1150, 1750, 3500 RPM.
Transmitted Horsepower
Power to be transmitted through the belt drive system.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Driver Pulley Diameter = 6, Driven Pulley Diameter = 12, Center Distance = 24, Motor Speed = 1750 = 5 input(s) provided
  2. Calculate Speed Ratio
    Speed Ratio
    2 = 2
  3. Calculate Belt Length
    Belt Length
    76.65 = 76.65
  4. Calculate Belt Speed
    Belt Speed
    2749 = 2749
  5. Calculate Tight Side Tension
    Tight Side Tension
    94.3 = 94.3

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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