Pump Capacity Calculator

Size your irrigation pump by calculating water horsepower, brake horsepower, required motor size, and daily energy costs.

Results

Water HP-

Brake HP-

Motor Power (kW)-

Energy Cost/day-

Motor Size (HP)-

Formula & How It Works

Water HP = (GPM × Head ft) ÷ 3960

3960 = 33,000 ft-lb/min per HP ÷ 8.34 lb/gal, the hydraulic power constant.

Brake HP = Water HP ÷ Pump Efficiency%

Motor kW = BHP × 0.7457 ÷ Motor Efficiency%

Motor Size = BHP × 1.25 (25% safety factor)

Calculation Example

500 GPM at 100 ft TDH: WHP = 50,000÷3960 = 12.63 HP. At 70% pump eff: BHP = 18.04 HP. Motor 90%: 14.95 kW. At $0.12/kWh × 8hr = $14.35/day. Motor size: 23 HP.

How to Use This Calculator

1. Required flow rate. 2. TDH (elevation + friction + pressure). 3. Pump/motor efficiency. 4. Electricity rate and hours. Calculate.

About This Tool

Proper pump sizing ensures flow and pressure while minimizing energy. TDH includes elevation lift, friction loss in pipes/fittings, and required operating pressure at the discharge.

Applicability: Suitable for irrigation planning in North America and Europe, adaptable to semi-arid and Mediterranean climates worldwide.

References & Sources:

Source: USDA NRCS, Irrigation Water Management Guide, National Engineering Handbook, Part 652, 2024.
Reference: FAO Irrigation and Drainage Paper 56, Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements, 2023.
Reference: ASABE Standard S437.1, Irrigation Scheduling and Water Application Efficiency.

Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.

Common Mistakes & Tips

Ignoring friction loss in TDH. Using BEP flow for all conditions. Not accounting for voltage drop. Oversizing motors wastes energy.

References & Sources

FAO (Food and Agriculture Organization) — Agricultural production and nutrition guidelines
USDA NRCS — Field Office Technical Guide and conservation practice standards
Land-Grant University Cooperative Extension System — crop and livestock recommendations
FAO — Water for Agriculture
USBR — Water Management

Frequently Asked Questions

What is TDH? ▼

Elevation lift + friction loss (pipes/fittings) + pressure head (operating pressure × 2.31 ft/psi).

Typical pump efficiency? ▼

Centrifugal 60-80% at BEP. Submersible 55-75%. Worn pumps 10-20% less.

Reduce energy costs? ▼

VFD drives, regular maintenance, right-sized pipes, off-peak rates, pressure regulation.

What units does the Pump Capacity Calculator use? ▼

Flow in GPM, total dynamic head in feet, pump/motor efficiency in %, electricity in $/kWh, operating hours/day unitless. Results in HP, kW, and $/day.

How do I use the Pump Capacity Calculator correctly? ▼

Start by gathering accurate input values from your farm records or measurements. Enter each value in the specified units, then click Calculate. Review all results carefully — cross-check the primary output against your own experience or extension recommendations. For best results, use actual measured values rather than estimates, and recalibrate whenever conditions change.