Pump Sizing Calculator: With Horsepower (hp) Chart

Written By Adam Paul – Waterproofing Expert

Pump sizing calculator is a digital tool that helps to calculate the size of the sump pump (in GPH and horsepower) by considering the basement area, average annual rainfall, soil type, groundwater level, lifting height, discharge distance, and battery backup system. The pump sizing calculator is a simple and powerful tool designed by Aqviz Waterproofing to help homeowners estimate the ideal sump pump size.

Follow these 7 steps to use the pump sizing calculator

Enter your basement area in square feet (sq. ft).
Input average annual rainfall (in inches) for your location. Use local weather data or NOAA estimates.
Choose your soil type around the basement. Soil type affects how quickly water drains through the ground.
Select the groundwater level based on whether your home experiences persistent dampness or flooding.
Add vertical lift (height in feet) of the sump pump from the sump pit to where the water exits your home.
Enter the discharge pipe length (in feet) of the sump pump. Longer distances create more pressure.
Choose whether you want a battery backup sump pump system for added flood protection during power outages.

Sump Pump Size Chart

A sump pump size chart is a summarized table that include horsepower (HP) of a sump pump to your basement size, water inflow rate, discharge height, and drainage distance. It simplifies the decision-making process by linking real-world conditions to the right pump capacity.

Horsepower	Gallons Per Hour (GPH) @ 10 ft lift	Basement Size	Inflow Conditions	Recommended Use Case
1/4 HP	1,500 – 1,800 GPH	Up to 1,000 ft²	Low inflow, gravel soil	Crawlspaces, small basements with good soil drainage
1/3 HP	2,400 – 2,800 GPH	1,000 – 1,500 ft²	Moderate rain, loamy soil	Standard residential basements
1/2 HP	3,000 – 3,800 GPH	1,500 – 2,500 ft²	High water table, clay soil	Homes in flood-prone or poorly drained areas
3/4 HP	4,000 – 4,800 GPH	2,500 – 3,500 ft²	Frequent heavy rain, deep pits	Deep basements, long discharge distances
1 HP	5,000 – 6,500+ GPH	3,500+ ft²	Severe flooding, commercial use	Apartments, large homes, or combined drainage systems

You have calculated the sump pump size, so what is next?

How to Calculate the Sump Pump Capacity?

Sump pump capacity refers to the maximum amount of water a sump pump can move within a specific time, usually measured in GPH (gallons per hour) or GPM (gallons per minute). The sump pump capacity explains how effectively the pump can keep your basement or crawl space dry during rainstorms, flooding, or rising groundwater.

To calculate the sump pump capacity, you should know these 6 factors, including basement area, average annual rainfall, soil type, water table level, vertical lift, and discharge distance.

How to calculate sump pump capacity?

Find the gallons per inch of rainfall: Basement Area × 0.623 × Soil Factor
Find the annual water volume: Gallons per inch × Rainfall × Water Table Multiplier
Find the average daily gallons: Annual Gallons ÷ 365
Find the hourly GPH needed with a safety factor: Daily Gallons ÷ 24 × 1.2
Determine the horsepower recommendation based on GPH
- < 2000 GPH needs a 1/4 HP sump pump
- 2000–3000 GPH needs a 1/3 HP sump pump
- 3000–5000 GPH needs a 1/2 HP sump pump

Example:

Area = 1,200 sq. ft.
Rainfall = 40 inches
Soil = clay (factor 0.9)
Water table = high (1.3)
Hourly GPH ≈ 2,336
Recommended Pump: 1/3 HP with optional backup

Read More About: How Does a Sump Pump Work?

How to Calculate GPH in a Sump Pump?

The GPH of a sump pump is the number of gallons per hour that a sump pump can pump out. To determine the GPH of a sump pump, you need to estimate how much water your basement collects from rain and groundwater, and how quickly that water needs to be removed.

Formula: Sump Pump GPH = (Area × 0.623 × Soil Factor × Rainfall × Water Table Factor ÷ 365 ÷ 24) × 1.2

How to calculate GPH in a Sump Pump?

6 Steps to calculate GPH in a sump pump

Find the basement area
Multiply by 0.623 (0.623 converts square feet and inches of rainfall to gallons of water.): Area × 0.623 = gallons/inch
Add soil type adjustment factor (Clay = 0.9, Loam = 0.7, Sand = 0.5, Gravel = 0.3): Gallons/inch × Soil Factor = adjusted gallons/inch
Add local annual rainfall data: Adjusted gallons/inch × Rainfall = total annual gallons
Adjust for water table pressure (high=1.3, moderate=1.0, low=0.8) = Annual Gallons × Water Table Factor = adjusted annual gallons
Convert to daily and hourly flow:
- Daily average: Annual Gallons ÷ 365
- Hourly Flow (add 20% safety margin): (Daily Gallons ÷ 24) × 1.2 = required GPH

Example:

Let’s say your basement has:

Basement area: 1,000 sq. ft.
Soil type: Clay soil (0.9)
Annual rainfall: 40 inches of rainfall/year
Water table level: High water table (1.3)

Step-by-step calculation for sump pump GPH

1,000 × 0.623 = 623 gallons/inch
623 × 0.9 = 560.7 adjusted gallons/inch
560.7 × 40 = 22,428 gallons/year
22,428 × 1.3 = 29,156.4 gallons/year
29,156.4 ÷ 365 = 79.9 gallons/day
79.9 ÷ 24 × 1.2 = 3.99 GPH ≈ 80 GPH

In real scenarios, sudden heavy rains can drastically increase flow. That’s why most basements need pumps rated for 2,000–5,000 GPH to handle peak loads.

Read More About: 5 Types of Sump Pumps with Pros and Cons

How to Calculate the Static Head for a Sump Pump?

The static head of the sump pump is the vertical distance (in feet) from the water level in the sump pit to the highest point in the discharge line before gravity takes over. Static head is measured by the meter of feet.

Formula: Static Head (ft) = Vertical height from sump water level to highest discharge point

How to calculate the static head for sump pump?

Measure the water level in the sump basin
Measure to the highest point of the discharge pipe
Take to height difference of the above two points

Example:
If the water level in your sump pit is 2 ft below the floor, and your discharge pipe rises 8 ft vertically before exiting outside the house:

Static Head = 8 ft

How to Calculate the Sump Pump Horsepower?

Sump pump horsepower (HP) is the power needed to move a specific amount of water (measured in GPH or gallons per hour) at a given static head height.

Formula: HP = (GPM × Head (ft) × 0.00231) / Pump efficiency

Where:

GPM = Gallons per minute
Head = Vertical lift in feet (static head)
0.00231 = Conversion factor
Efficiency = Pump efficiency (usually 40%-60%)

How to Calculate Sump Pump Flow Rate?

The sump pump flow rate, also known as the discharge rate, measures how much water your sump pump can move per hour. Typically it measures in GPH (gallons per hour) or GPM (gallons per minute).

Formula: GPH = (Basement Area × 0.623 × Soil Factor × Rainfall × Water Table Factor) ÷ 365 ÷ 24 × 1.2

Where: