Pulley Rpm Calculation Formula

Pulley RPM & Speed Calculator

Calculation Results:

Driven Pulley Speed (N2): 0 RPM

Speed Ratio: 0:1

Mechanical Advantage: 0

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Understanding the Pulley RPM Calculation Formula

In mechanical engineering and industrial maintenance, determining the speed of a driven pulley based on the motor's speed and pulley sizes is a fundamental task. This relationship is governed by the conservation of linear belt speed, assuming no slippage occurs.

The Fundamental Formula

The core mathematical relationship between two pulleys connected by a belt is expressed as:

D1 × N1 = D2 × N2

Where:

• D1 = Diameter of the Driver Pulley (usually attached to the motor)
• N1 = Revolutions Per Minute (RPM) of the Driver Pulley
• D2 = Diameter of the Driven Pulley (the load)
• N2 = Revolutions Per Minute (RPM) of the Driven Pulley

How to Solve for Driven RPM (N2)

To find the output speed, we rearrange the formula to isolate N2:

N2 = (D1 × N1) / D2

Real-World Example Calculation

Suppose you have a motor running at 1725 RPM with a 4-inch pulley attached (Driver). You want to connect it to a machine with a 10-inch pulley (Driven). What is the resulting speed?

1. Multiply D1 by N1: 4 × 1725 = 6900
2. Divide the result by D2: 6900 / 10 = 690
3. Result: The driven pulley will rotate at 690 RPM.

Key Rules to Remember

When using the pulley RPM calculator, keep these physics principles in mind:

• Inverse Relationship: As the diameter of the driven pulley increases, its speed (RPM) decreases, but its torque increases.
• Unit Consistency: Ensure both diameters (D1 and D2) use the same unit (e.g., both in inches or both in millimeters).
• Speed Ratio: The ratio is calculated as D2 / D1. If the ratio is 2:1, the driven pulley is twice as large and rotates at half the speed of the motor.

function calculatePulleyRPM() { var d1 = parseFloat(document.getElementById('driverDia').value); var n1 = parseFloat(document.getElementById('driverRPM').value); var d2 = parseFloat(document.getElementById('drivenDia').value); var resultDiv = document.getElementById('pulleyResult'); if (isNaN(d1) || isNaN(n1) || isNaN(d2) || d1 <= 0 || n1 <= 0 || d2 <= 0) { alert("Please enter valid positive numbers for all fields."); resultDiv.style.display = 'none'; return; } // Calculation Logic: N2 = (D1 * N1) / D2 var n2 = (d1 * n1) / d2; var ratio = d2 / d1; var advantage = d2 / d1; // Torque advantage is proportional to diameter ratio document.getElementById('resRPM').innerText = n2.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resRatio').innerText = ratio.toFixed(2); document.getElementById('resAdvantage').innerText = advantage.toFixed(2) + "x Torque Multiplier"; resultDiv.style.display = 'block'; }