How to Calculate Horsepower of a Pump

Pump Horsepower Formula:

\[ HP = \frac{Q \times H \times SG}{3960 \times \eta} \]

Flow Rate (Q):

gpm

Head (H):

Specific Gravity (SG):

unitless

Efficiency (η):

decimal

Required Horsepower (HP):

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1. What is Pump Horsepower Calculation?

Pump horsepower calculation determines the power required to move fluid through a pumping system. It considers flow rate, head pressure, fluid properties, and pump efficiency to ensure proper pump selection and operation.

2. How Does the Calculator Work?

The calculator uses the pump horsepower formula:

\[ HP = \frac{Q \times H \times SG}{3960 \times \eta} \]

Where:

\( HP \) — Horsepower (required power)
\( Q \) — Flow rate in gallons per minute (gpm)
\( H \) — Total head in feet (ft)
\( SG \) — Specific gravity of fluid (unitless)
\( \eta \) — Pump efficiency (decimal, typically 0.6-0.8)
\( 3960 \) — Conversion constant

Explanation: The formula calculates the mechanical power needed to overcome hydraulic resistance and move fluid through the system, accounting for pump efficiency losses.

3. Importance of Horsepower Calculation

Details: Accurate horsepower calculation is essential for proper pump selection, energy efficiency, system design, and preventing motor overload or underperformance.

4. Using the Calculator

Tips: Enter flow rate in gpm, head in feet, specific gravity (1.0 for water), and pump efficiency as decimal (0.6-0.8 typical). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is specific gravity and when should I change it?
A: Specific gravity is the ratio of fluid density to water density. Use 1.0 for water, higher for denser fluids, lower for lighter fluids.

Q2: What is a typical pump efficiency range?
A: Most centrifugal pumps operate at 60-80% efficiency (0.6-0.8). Higher efficiency pumps may reach 85-90%.

Q3: How do I determine total head?
A: Total head includes static head (vertical distance) plus friction losses in pipes, valves, and fittings.

Q4: Should I add a safety factor to the calculated horsepower?
A: Yes, typically add 10-20% safety margin to account for system variations and future requirements.

Q5: Can this formula be used for all pump types?
A: This formula works best for centrifugal pumps. Positive displacement pumps may require different calculations.