Sump Pump Size Calculator

Adam-Paul
Guided By Adam Paul - Waterproofing Expert

You Have claculted the sump pump size so What is Next?

  1. 7 Best Sump Pump for Basement and Crawlspace
  2. Sump Pump: How Does it Work, Specifications, Discharge, and Benefits
  3. How to Install a Sump Pump?
  4. How to Replace a Sump Pump?

How to use the Sump Pump Size Calculator?

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

What is a Sump Pump Size Calculator?

Sump pump 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, ground water level, lifting height, discharge distance, and battery backup system. Sump pump calculator is a simple and powerful tool designed by Aqviz Waterproofing to help homeowners estimate the ideal sump pump size.

How to Calculate the Size of the Sump Pump?

To find the size of the sump pump, you should calculate the sump pump capacity, GPH, static head, horsepower, and flow rate. By considering all of these, you can choose a suitable sump pump for your task. So let’s see how you can calculate these things properly.

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?

  1. Find the gallons per inch of rainfall: Basement Area × 0.623 × Soil Factor
  2. Find the annual water volume: Gallons per inch × Rainfall × Water Table Multiplier
  3. Find the average daily gallons: Annual Gallons ÷ 365
  4. Find the hourly GPH needed with a safety factor: Daily Gallons ÷ 24 × 1.2
  5. 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

  1. Find the basement area
  2. Multiply by 0.623 (0.623 converts square feet and inches of rainfall to gallons of water.): Area × 0.623 = gallons/inch
  3. Add soil type adjustment factor (Clay = 0.9, Loam = 0.7, Sand = 0.5, Gravel = 0.3): Gallons/inch × Soil Factor = adjusted gallons/inch
  4. Add local annual rainfall data: Adjusted gallons/inch × Rainfall = total annual gallons
  5. Adjust for water table pressure (high=1.3, moderate=1.0, low=0.8) = Annual Gallons × Water Table Factor = adjusted annual gallons
  6. 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. 1,000 × 0.623 = 623 gallons/inch
  2. 623 × 0.9 = 560.7 adjusted gallons/inch
  3. 560.7 × 40 = 22,428 gallons/year
  4. 22,428 × 1.3 = 29,156.4 gallons/year
  5. 29,156.4 ÷ 365 = 79.9 gallons/day
  6. 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?

  1. Measure the water level in the sump basin
  2. Measure to the highest point of the discharge pipe
  3. 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

Read More About: 6 Signs of Sump Pump Failures: Reasons and What to Do?

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? (Discharge 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:

  • 0.623 = Gallons of water per inch of rain per sq. ft.
  • Soil factor = Clay (0.9), Loam (0.7), Sand (0.5), Gravel (0.3)
  • Water table factor = High (1.3), Moderate (1.0), Low (0.8)
  • 1.2 = Safety margin for surge capacity

Example:

  • Basement area: 1,000 sq. ft.
  • Annual rainfall: 40 inches
  • Soil type: Loam (factor 0.7)
  • Water table: Moderate (factor 1.0)

Step-by-step calculation to find GPH:

  1. Gallons per inch = 1,000 × 0.623 × 0.7 = 436.1 gal/inch
  2. Total annual volume = 436.1 × 40 × 1.0 = 17,444 gallons/year
  3. Daily average = 17,444 ÷ 365 = 47.8 gal/day
  4. Hourly demand = 47.8 ÷ 24 × 1.2 = 2.39 GPH

How to Calculate Sump Pit Size?

To calculate the sump pit size, you should grab the Aqviz sump pump size calculator result and then design a custom sump basin as follows.

1. Estimate the peak inflow with a safety factor per minute

Start by estimating the maximum water inflow into the sump pit during heavy rain.

If you’re using a standard 18-inch diameter pit:

  • Each vertical inch of water ≈ 1 gallon
  • Use a safety factor of 1.5× to account for sudden surges and flow delays

Formula:
GPM (gallons per minute) = inches per minute × 1 gal/in × 1.5 (safety factor)

Example:
If your pit fills 20 inches per minute:
GPM = 20 × 1 × 1.5 = 30 GPM

2. Determine sump pump capacity per minute

Convert your pump’s GPH rating into GPM so you can compare it directly with the inflow rate.

Formula:
Pump capacity per minute (GPM) = GPH ÷ 60

Example:
If you use a pump rated at 1,800 GPH:
1800 ÷ 60 = 30 GPM

3. Calculate the minimum sump pit volume

Your sump pit needs to hold at least the full inflow per minute ; otherwise, water will back up before the pump can react.

Use the formula for cylindrical volume:

Formula:
Volume (gal) = (π × r² × height in feet) × 7.48 gal/ft³

For an 18-inch (1.5 ft) diameter pit:

  • Area = π × (0.75)² ≈ 1.77 ft²
  • Volume = 1.77 × Height × 7.48

Target volume: 30 gallons
Solve for height:

30 = 1.77 × H × 7.48
H ≈ 2.26 ft

You can round this up to 2.5 feet for safety.

Recommended sump pit dimensions

  • Diameter: 18-24 in (≈ 45-60 cm)
  • Depth: 24-30 in (≈ 60-76 cm)
  • Material: polyethylene, polypropylene or concrete basin
  • Cover: tightly fitting removable top
  • Base: use 4-6 in gravel under basin if water table is high

What is a Sump Pump Horsepower Chart?

A Sump Pump Horsepower Chart is a sizing guide that helps match the correct 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

What are the Problems of Choosing an Insufficient Sump Pump and Sump Pit?

Aqviz experts have encountered these 15 problems when a homeowner chooses an insufficient sump pump or an undersized sump pit.

  1. Basement flooding during heavy rain
  2. Short cycling and frequent pump activation
  3. Premature pump burnout or motor failure
  4. Backflow or discharge pipe backup
  5. Water is pooling around the foundation walls
  6. Mold, mildew, and excess basement humidity
  7. Damage to stored belongings and furniture
  8. Increased energy consumption and higher bills
  9. Building code violations and failed inspections
  10. Denied insurance claims due to undersized systems
  11. Inability to manage high water tables
  12. sump pit overflow in multi-source drainage setups
  13. Reduced pump lifespan from continuous operation
  14. Foundation cracks due to hydrostatic pressure
  15. High noise levels from overworked or cycling pumps