Pump Motor Capacity Calculator

Pump Motor Capacity Formula:

\[ \text{Capacity (HP)} = \frac{\text{Flow Rate (GPM)} \times \text{Head (feet)} \times \text{Specific Gravity}}{3960} \]

Pump Motor Capacity:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Pump Motor Capacity?

Pump motor capacity, measured in horsepower (HP), represents the power required by a pump to move fluid at a specified flow rate against a given head, accounting for the fluid's specific gravity. It's a critical parameter in pump selection and system design.

2. How Does the Calculator Work?

The calculator uses the pump capacity formula:

\[ \text{Capacity (HP)} = \frac{\text{Flow Rate (GPM)} \times \text{Head (feet)} \times \text{Specific Gravity}}{3960} \]

Where:

Flow Rate — Gallons per minute (GPM) of fluid being pumped
Head — Total dynamic head in feet that the pump must overcome
Specific Gravity — Ratio of fluid density to water density (water = 1.0)
3960 — Conversion factor to horsepower

Explanation: The formula calculates the theoretical horsepower required, not accounting for pump efficiency. Actual motor size should include a safety factor.

3. Importance of Pump Capacity Calculation

Details: Proper pump sizing ensures efficient operation, prevents motor overload, and reduces energy costs. Undersized pumps can't meet demand while oversized pumps operate inefficiently.

4. Using the Calculator

Tips: Enter flow rate in GPM, head in feet, and specific gravity (1.0 for water). For viscous fluids, additional corrections may be needed. Always consult an engineer for critical applications.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between theoretical and actual HP?
A: Theoretical HP doesn't account for pump efficiency. Actual HP = Theoretical HP / Pump Efficiency. Always include efficiency in final motor selection.

Q2: How does viscosity affect the calculation?
A: High viscosity fluids require more power. For viscosities > 50 cP, consult viscosity correction charts or specialized calculators.

Q3: What safety factor should I use?
A: Typical safety factors range from 10-25% depending on application. Critical services may require higher factors.

Q4: Can I use this for centrifugal and positive displacement pumps?
A: This formula works best for centrifugal pumps. Positive displacement pumps require different calculations accounting for pressure and volumetric efficiency.

Q5: How do I convert to metric units?
A: For metric (kW): HP × 0.746 = kW. Flow in m³/h and head in meters require different constants in the formula.