Agitator Power Calculator

The Agitator Power Calculator estimates agitator power requirement in kilowatts. Simply enter the power number, fluid density, impeller speed, and impeller diameter to calculate your agitator power in kW and W. The result shows the mechanical power needed at the impeller shaft for mixing tanks. This calculator helps Indian engineers and plant operators better understand mixing equipment sizing for industrial processes. This calculator also calculates agitator power in watts (W).

Enter the impeller power number (e.g., 5.0 for a standard Rushton turbine)
Enter fluid density in kg per cubic metre (e.g., 1000 for water)
Enter rotational speed in revolutions per minute (e.g., 100)
Enter impeller diameter in metres (e.g., 0.5)

This calculator is for informational purposes only. Verify results with appropriate professionals for important decisions.

Enter your values in the form above, then click Calculate to see your agitator power requirement. Use the preset examples to test common mixing scenarios. You can share your calculation or download a PDF copy for your engineering records.

What Is Agitator Power Requirement

Agitator power requirement is the amount of mechanical power needed to rotate an impeller inside a tank of fluid. It tells you how strong the motor must be to turn the impeller at the chosen speed. The value depends on the fluid weight, impeller size, spinning speed, and impeller shape. Engineers across India use this number to pick the right motor for mixing tanks in factories, water treatment plants, and chemical processing units.

How Agitator Power Requirement Is Calculated

Formula

P = Np × ρ × n3 × D5

Where:

  • P = agitator power in watts (W)
  • Np = power number of the impeller (dimensionless)
  • ρ = fluid density in kg/m3
  • n = rotational speed in revolutions per second (s-1), where n = N ÷ 60
  • N = rotational speed in revolutions per minute (rpm)
  • D = impeller diameter in metres (m)
  • P(kW) = P(W) ÷ 1000

The formula multiplies four things together. First, the power number describes how much resistance the impeller shape creates in the fluid. Second, fluid density shows how heavy the liquid is. Third, the speed is changed from rotations per minute to rotations per second, then raised to the third power because faster spinning needs much more force. Fourth, the impeller diameter is raised to the fifth power because a bigger impeller moves much more liquid. When all four parts multiply, you get power in watts. Dividing by one thousand changes watts to kilowatts, which is the unit Indian engineers use to size motors.

Why Agitator Power Requirement Matters

Knowing the agitator power requirement helps you choose the right motor for your mixing tank. It also helps you compare impeller designs and plan energy costs before buying equipment. This number guides safe and efficient mixing in many Indian industries.

Why Correct Power Estimation Is Important for Equipment Selection

Choosing a motor that is too small may cause it to overload, overheat, or fail during operation. A motor that is too large wastes electricity and increases cost. Incorrect power estimates may also damage the impeller shaft, bearings, or gearbox over time. Estimating the agitator power requirement carefully may help avoid costly breakdowns, reduce downtime, and support safer plant operation. It is recommended to verify the result with a qualified mechanical engineer before final selection.

For Equipment Sizing and Motor Selection

The calculated power helps you pick a motor that can handle the mixing load. Indian engineers may consider adding a safety margin of ten to twenty percent to account for startup loads and changes in fluid properties. The result may serve as a starting point for selecting gearbox ratings, motor frame sizes, and electrical supply requirements for the mixing system.

For Advanced Users Working with Viscous Fluids

The standard power number stays constant only in turbulent flow. For viscous or non-Newtonian fluids, the power number may change with the Reynolds number. Advanced users may consider calculating the Reynolds number first and then checking the impeller's power number curve. This correction may improve accuracy for slow mixing of thick liquids like slurries, syrups, or polymer solutions used in Indian process industries.

Agitator Power Requirement vs Motor Rated Power

Agitator power requirement is the mechanical power needed at the impeller shaft. Motor rated power is the electrical power the motor can deliver, which is usually higher due to efficiency losses, gearbox losses, and safety factors. A common mistake is to choose a motor with the same rating as the calculated agitator power, which may cause overloading. It is recommended to divide the agitator power by motor efficiency and add a service factor.

Calculation logic verified using publicly available standards.

View our Accuracy & Reliability Framework →