Sump Pump Size Calculator

Guided By Adam Paul - Waterproofing Expert

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

How to use the Sump Pump Size 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.

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 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? (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:

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

What You Should Know Before Calculating the Sump Pump?

You should know the basement area, average annual rainfall, soil type, water table level, vertical lift, discharge distance, and battery backup system before calculating a sump pump size, capacity, GPH, static head, discharge rate, and horsepower.

Basement Area of the Sump Pump to Be Used

The basement area is the total floor surface of your basement. The larger basement area accumulates more water for the sump pump, while the smaller basement area accumulates less water amounts to the sump pump. The basement area is measured in square feet (sq. ft.). It’s the horizontal footprint of the space that could potentially collect or channel water during rainfall, groundwater rise, or plumbing issues.

At Aqviz, we always begin with square footage because it directly influences how much water can infiltrate your foundation or slab. The larger the basement, the higher the potential for water collection during heavy rainfall or flooding events.

In metric terms, 1 sq. ft. = 0.0929 m², but since we tailor this for U.S. homeowners, sq. ft. is the standard

Average Annual Rainfall of the Sump Pump Used Region

Average annual rainfall is the total depth of precipitation, primarily rain, that falls in your area over a calendar year. This value is measured in inches (in.) and typically reflects long-term weather data.

At Aqviz, we factor this in because it tells us how often and how much water your sump pump may need to handle over time. The higher the annual rainfall, the greater the cumulative water load your basement is exposed to, especially if your property has drainage or grading issues.

The average rainfall is measured by Inches per year (in./yr). We use it with a factor for the sump pump calculator.

Rainfall combines with your basement area and soil absorption to estimate how much water enters your sump system annually.

The rainfall multiplier increases or decreases the total volume based on your local weather data.
If you live in a wet region (e.g., parts of Oregon or Florida), you may receive 40-60 inches of rain annually, meaning a heavier-duty sump pump is essential.

How to find the average rainfall value in your region?

You can use NOAA or your local weather bureau
You can check city rainfall averages. As examples
- Seattle, WA, average rainfall value is 37 in/year
- Portland, OR, average rainfall value is 43 in/year
- Chicago, IL, average rainfall value is 36 in/year
- Miami, FL, average rainfall value is 61 in/year

Soil Type of the Sump Pump Used Area

Soil type is the dominant ground composition around your foundation or under your basement slab. It directly affects how water infiltrates or drains through the ground that the sump pump need to pump out. Soil is categorized based on particle size and permeability.

At Aqviz, we’ve seen firsthand how drainage rates vary drastically between soil types. Some soils retain water like a sponge, while others let it drain freely. This influences the soil factor in our calculator, which adjusts the estimated gallons of water your sump pump must move.

Soil Type	Description	Soil Factor
Clay	Dense, compact, poor drainage	`0.9`
Loam	Balanced mix, moderate drainage	`0.7`
Sand	Coarse, good drainage	`0.5`
Gravel	Very porous, excellent drainage	`0.3`

*If the soil type is unknown, we apply a default fallback factor of 0.6

How to identify your soil type near the basement?

Use a local soil survey (via USDA Web Soil Survey)
Dig a 6″ hole and run a percolation test:
- Slow absorption = clay or loam
- Fast draining = sand or gravel

Water Table Level in Sump Pump Used Area

The water table is the upper surface of the underground water in the soil. It rises and falls based on rainfall, drainage, and geology. The water table level describes how close the water is to your basement floor. We categorize it into three levels:

High: Water table is near or above the basement slab
Moderate: Water table is below the slab but may rise during rainy seasons
Low: Water table is deeper in groundwater, not typically a concern

From our experience at Aqviz, properties with a high water table are far more prone to seepage, hydrostatic pressure, and continuous sump pump operation even during dry weather. It’s not just about rainfall, it’s about constant groundwater pressure trying to push up into your basement.

Water Table Level	Description	Water Factor
High	Persistent hydrostatic pressure	`1.3`
Moderate	Seasonal rise, occasional pressure	`1.0`
Low	Rare risk of pressure or flooding	`0.8`

How to determine your water table?

To determine the water table, you can ask your local building department or county surveyor

Look for signs like:
- Persistent sump pump activity year-round
- Foundation dampness even during droughts
- Groundwater in post holes or test pits

Vertical Lift of the Sump Pump

Vertical lift (also called static head) is the vertical distance the sump pump must lift water from the sump pit up to the discharge outlet. It’s measured in feet (ft), and directly affects pump workload and performance.

At Aqviz, we always emphasize vertical lift because it has a direct impact on flow rate and horsepower selection. As lift increases, pump efficiency decreases. A 1/3 HP pump might handle 2,500 GPH at 5 ft but only 1,200 GPH at 10 ft.

While the calculator doesn’t reduce GPH based on lift, we include this input to flag whether you need a higher horsepower pump.

0-7 ft for Standard sump pump lift
8-12 ft for Medium sump pump lift
13+ ft for High sump pump lift (consider 1/2 HP+)

We use the calculated GPH to choose the right horsepower, then cross-check if the lift exceeds what the selected pump can support efficiently.

How to measure sump pump lift?

Measure from the bottom of the sump pit (where the pump sits) up to the point where the discharge pipe exits your home.
Don’t forget to include any check valves or elbows, each adds minor resistance (we typically build in a buffer).

Discharge Distance of the Sump Pump

Discharge distance is the total length of the pipe that carries water horizontally from the sump pump to the final drainage point (yard, storm drain, dry well, etc.). It’s measured in feet (ft) and includes all elbows, joints, and exterior piping.

At Aqviz, we’ve installed systems where long or poorly sloped discharge lines created back pressure that burned out pumps early. The longer the distance, the more friction loss, and the more resistance your pump has to overcome. Combined with vertical lift, this defines your total dynamic head (TDH).

While our current calculator doesn’t yet reduce GPH based on discharge length, we log this input to help interpret the GPH vs HP recommendation. Longer distances push the selected pump closer to its limit

Typically:

< 20 ft sump pump discharge: Sump pump requires minimal impact
20-50 ft sump pump discharge: Sump pump requires moderate resistance (watch for elbows) to discharge 20-50 ft.
50 ft sump pump discharge: Sump pump requires more power to discharge 50 ft.

Battery Backup Option for the Sump Pump

A battery backup system is an auxiliary sump pump or power source that activates during a power outage or primary pump failure. It typically consists of a DC-powered pump, a deep-cycle marine battery, and a charging controller.

At Aqviz, we strongly recommend battery backups, especially in areas with frequent storms, old electrical systems, or finished basements. The #1 cause of sump pump failure we’ve seen is power outage during heavy rain, exactly when the pump is most needed.

We use yes/no to the sump pump calculator. If