Horsepower Required to Pump Water Calculator

Horsepower Formula:

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

Flow Rate (Q):

GPM

Head (H):

feet

Specific Gravity (SG):

(dimensionless)

Pump Efficiency (η):

(decimal)

Required Horsepower (HP):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Pump Horsepower Calculation?

The horsepower required to pump water is calculated based on flow rate, head pressure, specific gravity of the fluid, and pump efficiency. This helps in selecting the right pump motor size for a given application.

2. How Does the Calculator Work?

The calculator uses the following formula:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( H \) — Total head in feet
\( SG \) — Specific gravity of the fluid (1.0 for water)
\( \eta \) — Pump efficiency as a decimal (typically 0.7-0.9)
3960 — Conversion factor to horsepower

Explanation: The formula calculates the power required to move a given flow rate against a specific head pressure, adjusted for fluid density and pump efficiency.

3. Importance of Horsepower Calculation

Details: Proper horsepower calculation ensures the pump motor is neither undersized (leading to failure) nor oversized (wasting energy and money). It's critical for system design and energy efficiency.

4. Using the Calculator

Tips:

For water, specific gravity is 1.0
Typical pump efficiency ranges from 70-90% (0.7-0.9)
Include total dynamic head (static head + friction losses)
Always add a safety factor (10-20%) to the calculated HP

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between hydraulic HP and brake HP?
A: Hydraulic HP is the theoretical power needed to move the fluid. Brake HP includes pump efficiency and is what the motor must deliver.

Q2: How does viscosity affect horsepower?
A: Higher viscosity fluids require more power to pump and may reduce pump efficiency.

Q3: What's a typical efficiency for centrifugal pumps?
A: Typically 70-85% for most centrifugal pumps, but can vary based on size and design.

Q4: Should I use the calculated HP directly for motor selection?
A: No, always round up to the next standard motor size and include a safety factor.

Q5: How does altitude affect horsepower requirements?
A: Higher altitudes reduce air density, which can affect motor cooling but doesn't change the hydraulic HP calculation.