Sump Pump Sizing Calculator

Purpose and model boundary

Intersects eight auditable generic pump curves with a routed discharge-system curve, then screens flow reserve, velocity, and optional cycling.

Do not treat this result as a hydraulic or plumbing design, flood-protection guarantee, code-compliance determination, permit approval, equipment selection, safety certification, cost quote, or endorsement by a cited source. Site geometry, rainfall, runoff, soil, pipe, pump, tank, irrigation, manufacturer, locally adopted code, and approval inputs remain the user's responsibility.

Inputs and units

• inflow basis: a listed route or text value.
• system loss method: a listed route or text value.
• selection objective: a listed route or text value.
• cycle check: a listed route or text value.
• direct peak inflow gpm: entered in gal/min.
• pit diameter in: entered in inches.
• measured rise rate in min: entered in inches per minute.
• inflow design factor: entered in factor.
• static lift ft: entered in ft.
• discharge length ft: entered in ft.
• discharge id in: entered in inches.
• hazen c: entered in coefficient.
• reference flow gpm: entered in gal/min.
• reference loss ft: entered in ft.
• maximum discharge velocity ft s: entered in ft/s.
• switch differential in: entered in inches.
• minimum cycle time min: entered in min.

The pump candidate grid contains 8 fixed data rows plus one header row with these columns: Include, Candidate label, Shutoff head (ft), Rated flow (gal/min), Head at rated flow (ft), Maximum modeled flow (gal/min), Input power (W), Purchase cost (user currency), Source note. Numeric columns retain the units shown here; text, route, and include columns are intentionally unitless.

Governing relationships

Source inflow is entered directly or calculated as:

Q_source = [pi(D_pit/12)^2/4] (r_rise/12) 7.48051948051948

Q_source is in gal/min, D_pit is pit diameter (in), and r_rise is measured rise (in/min). Required flow is:

Q_req = f_d Q_source

f_d is the inflow design factor.

For the Hazen-Williams route, the workbook keeps the system curve in feet:

h_f(Q) = 4.52 * 2.31 * L Q^1.852/(C^1.852 d^4.87)

The 4.52 expression produces psi and 2.31 ft/psi converts it once to feet. L is equivalent discharge length (ft), Q is gal/min, C is Hazen-Williams coefficient, and d is inside diameter (in). System head is:

H_sys(Q) = H_static+h_f(Q)

The reference-loss route instead uses:

H_sys(Q) = H_static+h_ref(Q/Q_ref)^2

Heads are in ft and flow is in gal/min.

Candidate pump head and curve coefficient are:

H_pump(Q) = H_0-k_p Q^2

k_p = (H_0-H_r)/Q_r^2

H_0 is shutoff head (ft), and (Q_r,H_r) is the rated point. Thirty fixed bisection steps solve:

H_pump(Q) = H_sys(Q)

from zero through the candidate maximum flow. Duty velocity is:

v_duty = (Q_duty/448.831168831169)/[pi(d/12)^2/4]

v_duty is in ft/s. With cycle checking active, switch volume is pit area times switch differential times 7.48051948051948, and cycle time is fill time plus pump-down time. Only candidates clearing required flow, velocity, and active cycle gates are ranked.

Calculation sequence

1. Validate every active selector, scalar bound, type, and every fixed-grid entry.
2. Apply the selected route and ignore values from inactive fields.
3. Normalize unit-dependent inputs into the workbook's calculation basis.
4. Evaluate every included row or candidate and aggregate the active schedule.
5. Calculate primary and supporting outputs, populate the authored chart series, and apply derived numeric checks.
6. Return the workbook status with the computed results; invalid input is never converted into a plausible engineering answer.

Outputs and interpretation

• required pump flow gpm (gal/min): Peak inflow after the planning factor.
• selected pump: Passing pump ranked by the active objective.
• duty flow gpm (gal/min): Fixed-bisection intersection of the selected generic pump and system curves.
• duty head ft (ft): System head at the calculated duty flow.
• cycle time min (min): Simplified fill time plus pump-down time across the entered switch differential.

The chart is an explanatory view of the workbook's named chart ranges. It does not add a separate calculation or replace the numeric outputs.

Validation and status logic

The workbook evaluates Model_Status in the order shown. The first matching condition wins.

Assumptions and limitations

• All shipped default pump curves, costs, and hydraulic values are synthetic illustrative demonstrations.

• All pump rows and costs are synthetic editable examples, not manufacturer data.

• The discharge system is represented by static lift plus one friction-loss route.

• Cycling is a simplified constant-inflow fill and pump-down balance.

• This does not size electrical supply, backup power, check valves, dual-pump controls, solids handling, alarms, basin freeboard, flood consequence, or code-required capacity.

• Replace every candidate with verified manufacturer curves and obtain qualified plumbing/electrical review.

Restrictions and non-computing states

Each numeric control offers a working range chosen for usable entry, which is not always the limit this calculator enforces; a value outside that limit is rejected with a message rather than quietly accepted. The calculator additionally enforces allowed choices, active-field types, complete fixed-grid rows, and conditional or cross-field rules before computing.

Unsupported route values, incomplete rows, out-of-domain inputs, relational failures, nonfinite derived arithmetic, and workbook error tokens are non-computing states. Hidden inputs remain in the values sent to the calculator but must not affect results while those fields are inactive.

Errors and warnings

A rejected entry means the submitted state failed the published input rules. Workbook NOT VALID identifies an invalid active domain or unsupported derived arithmetic. Workbook CHECK retains a finite result while flagging a planning condition that needs review. OK means only that the delivered workbook logic closed within the entered assumptions; it is not code compliance, professional approval, or a safety guarantee.

This version is checked against 129 saved test cases, covering both calculated results and entries that should be refused, run against this exact workbook.

• U.S. Department of Energy MEASUR - Primary public context for pump and system performance assessment. Official U.S. government source; equations are independently implemented.
• NIST volume units - Primary unit-conversion provenance for pit volume and gallons per minute. Official public U.S. government reference; conversions are independently implemented and no source material is copied.
• EPA WaterSense water-system resources - Public context for water efficiency and reviewed equipment assumptions. Official public U.S. government source; no proprietary product data is embedded.

Licensing conclusion: No licensed, proprietary, manufacturer, utility, product-price, code-table, forecast, or external dataset is embedded. The calculator independently implements general hydraulic, water-balance, and home-project engineering arithmetic from cited public and official sources; all defaults, labels, conductor/load rows, equipment assumptions, diagrams, and test values are synthetic illustrations.