Sump Pump Capacity Calculator (GPM & TDH)

Size basement sump pumps from measured or estimated inflow, pit geometry, vertical lift, and discharge pipe run — get required GPM, Total Dynamic Head, pit holding capacity, and recommended horsepower instantly.

Inflow Method

Input Mode

Basement Area (sq ft)

Soil Risk Profile

Sump Pit & Discharge

Pit Diameter (in)

Pit Depth (in)

Vertical Lift Height (ft)

Total Delivery Pipe Length (ft)

Safety Profile

Live Results

Recommended Pump Size

1/2 HP

Moderate Load — Mid-range pump required. Verify against manufacturer flow curve at calculated TDH.

Required System Flow

36.0 GPM

Total Dynamic Head (TDH)

14 ft

Pit Holding Capacity

26.4 Gallons

Required flow applies a safety multiplier to measured or estimated inflow. TDH accounts for vertical lift, pipe friction (0.10 ft/ft), and check valve resistance. HP selection evaluates both GPM and TDH together — verify against manufacturer pump curves before final selection.

How to Use This Sump Pump Capacity Calculator

Choose your inflow method. Switch between Live Inflow Test (measured GPM from a timed bucket test) and Basement Area Estimate (square footage with a soil risk profile). Sandy soils use 14 GPM per 1,000 sq ft; standard clay uses 20 GPM; high water table uses 30 GPM.
Enter sump pit and discharge geometry. Input pit diameter and depth to calculate holding capacity in gallons. Set vertical lift height and total delivery pipe length — these drive Total Dynamic Head (TDH) along with a fixed check valve allowance.
Select a safety profile. Apply a safety multiplier to base inflow: Normal Protection (1.25×), Heavy Influx (1.5×), or Extreme Flood Risk (2.0×). Required system flow equals base inflow multiplied by the safety factor.
Review pump size and redundancy guidance. The calculator evaluates required GPM and TDH together in a dual-variable HP matrix, then maps the recommended horsepower to a compliance badge — green for 1/4 and 1/3 HP single-pump installs, yellow for 1/2 and 3/4 HP mid- to heavy-duty loads, red when a dual pump system is required.

Formulas & Example

Base inflow comes from a live test or area estimate. Required flow applies a safety multiplier. TDH sums lift, pipe friction, and check valve head. Horsepower is selected from a dual-variable matrix that evaluates both required GPM and calculated TDH together.

Pit Radius (ft) = (Pit Diameter in ÷ 2) ÷ 12
Pit Depth (ft) = Pit Depth in ÷ 12
Pit Volume (gal) = π × Radius² × Depth × 7.48

Area Estimate Inflow = (Basement Sq Ft ÷ 1000) × Soil Multiplier
  Sandy = 14 GPM | Clay = 20 GPM | High Water Table = 30 GPM
Base Inflow = Live GPM OR Area Estimate
Required GPM = Base Inflow × Safety Factor
  Normal = 1.25× | Heavy = 1.5× | Extreme = 2.0×

TDH (ft) = Vertical Lift + (Pipe Length × 0.10) + 2.0

HP Selection (Required GPM + TDH):
  ≤ 15 GPM                          → 1/4 HP
  16–25 GPM, TDH ≤ 10 ft            → 1/4 HP
  16–25 GPM, TDH > 10 ft            → 1/3 HP
  26–35 GPM, TDH ≤ 10 ft            → 1/3 HP
  26–35 GPM, TDH > 10 ft            → 1/2 HP
  36–50 GPM, TDH ≤ 15 ft            → 1/2 HP
  36–50 GPM, TDH > 15 ft            → 3/4 HP
  > 50 GPM                          → 3/4 HP or Dual Pump System

Worked Example

1,200 sq ft basement, medium clay soil, heavy influx (1.5×), 18" × 24" pit, 10 ft lift, 15 ft pipe:

Base Inflow = (1200 ÷ 1000) × 20 = 24 GPM
Required GPM = 24 × 1.5 = 36.0 GPM
TDH = 10 + (15 × 0.10) + 2.0 = 13.5 ft → 14 ft

Pit Volume = π × 0.75² × 2 × 7.48 = 26.4 gal
Recommended Pump = 1/2 HP (36 GPM band, TDH ≤ 15 ft)
Load Badge = YELLOW — verify flow curve at calculated TDH

Switching to high water table soil (30 GPM per 1,000 sq ft) with the same safety factor raises required flow to 54 GPM — recommending 3/4 HP or Dual Pump System with a red Extreme Load badge on the same TDH.

Frequently Asked Questions

How do I measure live inflow rate (GPM)?▾

Run the pump and time how long it takes to fill a known volume — for example, a 5-gallon bucket. Divide gallons by minutes to get GPM. Take several readings during wet weather for a conservative peak estimate. Enter that measured value in Live Inflow Test mode.

What is Total Dynamic Head (TDH) for a sump pump?▾

TDH is the total head the pump must overcome: vertical lift from the pit water level to the discharge point, plus friction losses in the discharge pipe (this calculator uses 0.10 ft per foot of pipe run), plus 2.0 ft for check valve and fitting resistance. Match TDH and GPM together when selecting a pump from manufacturer curves.

How is pit holding capacity calculated?▾

Pit volume treats the sump basin as a cylinder: radius in feet times depth in feet times π, converted to gallons at 7.48 gallons per cubic foot. Holding capacity helps you assess cycle time — a larger pit reduces how often the pump runs during steady inflow.

When do I need a dual-pump or battery backup system?▾

When required system flow exceeds 50 GPM after the safety multiplier, this tool recommends 3/4 HP or Dual Pump System with a red Extreme Load badge — consult a licensed plumber or drainage engineer. Flows between 35 and 50 GPM may require 1/2 or 3/4 HP depending on TDH, with yellow badges prompting verification against manufacturer pump curves and pit drawdown cycle time.

How does TDH affect horsepower selection?▾

The same required GPM can need a larger motor when TDH is higher. For example, 20 GPM at 8 ft TDH stays at 1/4 HP, but 20 GPM at 12 ft TDH steps up to 1/3 HP. Above 25 GPM, TDH thresholds at 10 ft and 15 ft further split recommendations between 1/3, 1/2, and 3/4 HP. Always confirm the selected pump meets both GPM and TDH on the manufacturer curve.

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