Sump Pump Calculator
This free sump pump calculator computes the one number that actually determines whether a pump can keep your basement dry: Total Dynamic Head. A pump's headline "up to 60 GPM" is measured at zero head — pushing water straight up out of the pump with no pipe attached. Add eight feet of vertical lift, thirty feet of pipe, and a check valve, and that same pump might deliver 35 GPM. TDH is how you find the real number, and matching it to the pump's performance curve is how you avoid buying a pump that floods.
Enter your discharge path — the vertical lift from the pump to where the pipe exits above grade, the total pipe run, and the fittings on it — and the calculator sums the equivalent length using the SSPMA effluent-pump fitting values, computes friction head with the Hazen-Williams equation for Schedule 40 PVC, and adds your static lift. The result is the TDH at your design flow: the exact point that must fall on or below a candidate pump's curve.
The design flow itself comes from your basin — time how fast the pit fills during heavy rain and multiply by a 1.5–2× safety factor. The results also flag when pipe velocity exceeds the 5-feet-per-second guideline (step up a size), and note that a check valve is often the single biggest source of friction on a sump run. Reference math only — the manufacturer's pump curve governs the final pick. Free, no signup.
Sump Pump Calculator
What pump does your sump need? The number that matters is Total Dynamic Head — your vertical lift plus pipe friction — because a pump's "max GPM" is at zero head. Enter your discharge path for the TDH to match against a pump curve. Free, no signup.
Discharge path
Fittings on the run
Not sure of your basin inflow? Time how fast the pit refills during heavy rain (gallons ÷ minutes), then multiply by 1.5–2 for the design flow.
Calculation Formulas
The total resistance the pump works against. Static lift is the vertical rise; friction head is the loss to pipe and fittings.
Example:
8 ft lift + 6.3 ft friction = 14.3 ft TDH.
Each fitting adds resistance equal to some feet of straight pipe. Values default to the SSPMA effluent-pump guideline.
Example:
30 ft + 3 × 90° elbow (24 ft) + check valve (13 ft) = 67 ft.
Loss per 100 ft comes from the Hazen-Williams equation for Schedule 40 PVC at your flow.
Example:
67 ÷ 100 × 9.4 ft/100ft (1½" at 40 GPM) = 6.3 ft.
On the manufacturer's pump curve, the point (GPM, TDH) must fall on or below the line. The box's "max GPM" is at zero head — not your operating point.
Example:
Plot (40 GPM, 14.3 ft) against the curve.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| 90° elbow equivalent | 8.0 ft (1½") · 9.0 ft (2") | SSPMA effluent-pump guideline. |
| Check valve equivalent | 13.0 ft (1½") · 17.0 ft (2") | The single biggest fitting loss on most sump runs. |
| Friction at 40 GPM | 9.4 ft/100ft (1½") · 2.8 ft/100ft (2") | Sch 40 PVC, Hazen-Williams — 2" cuts friction dramatically. |
| Velocity guideline | ≤ 5 ft/s | Above this, step up pipe size to limit water hammer. |
| Worked example | 8 ft lift + 40 GPM → 14.3 ft TDH | The research anchor this calculator reproduces. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
SSPMA sizing method(Sump & Sewage Pump Manufacturers Association)
View StandardThe trade-association effluent-pump sizing workflow and fitting-equivalent table — members include Zoeller, Liberty, Franklin, Goulds/Xylem.
Key Requirements:
- •TDH = static + friction
- •Fitting equivalents by size
Hazen-Williams equation(C = 150 (PVC))
View StandardThe empirical friction-loss formula behind the per-100ft values; C is the pipe-roughness coefficient.
Key Requirements:
- •Valid ~60°F, turbulent flow
- •Velocity ≤ 5 ft/s
Manufacturer pump curves(Zoeller / Liberty / Goulds performance charts)
View StandardThe final authority — the duty point must lie on or below the published curve.
Key Requirements:
- •Confirm GPM at the computed TDH
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Basin inflow
The input you must measure
Design flow comes from how fast your pit fills under worst-case conditions, not a guess. Time the refill during heavy rain and multiply by 1.5–2× for headroom.
Regional Examples:
Discharge rules
Where the water may go
Many jurisdictions prohibit sump discharge into the sanitary sewer and regulate how far from the foundation and property line it may daylight; some require a dedicated storm connection.
Regional Examples:
Freeze protection
Cold-climate discharge
In freezing climates the discharge line must slope to drain and often needs a freeze-relief or air-gap fitting so a frozen outlet doesn't dead-head the pump.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Plan disposal before you start
Smaller jobs still produce more debris than a few trash bags can hold. Check what's allowed in a dumpster and which disposal option fits the scope.
See disposal options →
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How to Use This Calculator
- Estimate your design flow in GPM — time how fast the pit refills during heavy rain (gallons ÷ minutes) and multiply by 1.5–2 for headroom.
- Choose the discharge pipe size — 1½" for most 1/3–1/2 HP pumps, 2" for higher-flow or sewage pumps.
- Enter the static lift (vertical rise from pump to the pipe's exit above grade) and the total pipe run length.
- Add the fittings on the run with the steppers — 90° elbows, the check valve, and any others.
- Click Calculate for the friction head, Total Dynamic Head, and the duty point to match against a pump's performance curve.
Reading a pump curve
A pump-performance curve plots GPM (horizontal) against head in feet (vertical), sloping down to the right. Find your TDH on the vertical axis, read across to the curve, and drop down to the flow — that's what the pump actually delivers at your installation. If your design flow at your TDH falls below/left of the curve, the pump has margin; if it falls above/right, the pump can't keep up. Pick a pump whose curve puts your duty point comfortably in its mid-range.
Frequently Asked Questions
What size sump pump do I need?
Match two things: the flow your basin needs (GPM) and the Total Dynamic Head your discharge path creates. Estimate flow by timing how fast the pit fills during heavy rain and multiplying by 1.5–2×. Then compute TDH — static lift plus pipe friction — and find a pump whose performance curve delivers your flow at that head. A typical 1/3 HP pump handles about 8–10 feet of TDH at moderate flow; deeper pits, long runs, or high flow push you to 1/2 HP or more. The calculator gives you the exact TDH to shop against.
What is Total Dynamic Head on a sump pump?
TDH is the total resistance the pump works against — vertical static lift plus friction head from the pipe and fittings. It matters because a pump's advertised 'max GPM' is measured at zero head; real installations always have head, so real delivered flow is lower. A pump rated 60 GPM at zero head might give 35 GPM at 14 feet of TDH. You size by finding your TDH, then reading the pump's curve at that head to see the actual flow it delivers.
Does pipe size matter for a sump pump?
Enormously — it's the cheapest way to cut friction. At 40 GPM, 1½" PVC loses about 9.4 feet of head per 100 feet, while 2" loses only 2.8 — roughly a third. On a long discharge run, upsizing the pipe can drop your TDH by several feet and let a smaller pump do the job. Watch velocity too: over about 5 feet per second the run gets loud and prone to water hammer, another signal to go up a size. Never neck the discharge below the pump's outlet size.
How much head does a check valve add?
More than most people expect — it's often the single biggest fitting loss on a sump run. Per the SSPMA effluent-pump data, a check valve adds the equivalent of 13 feet of straight pipe in 1½" and 17 feet in 2". That's why a short run with a check valve and a couple of elbows can still build meaningful friction head. You still need the check valve — it stops the vertical column of water from draining back into the pit and short-cycling the pump — just account for it in the TDH.
How do I estimate my sump basin's inflow rate?
During heavy rain, let the pump cycle, then unplug it and time how long the water takes to rise a measured amount in the pit — or time a full pump-out and refill. Convert to gallons per minute (a standard 18"-diameter basin holds about 1.3 gallons per inch of depth). Multiply the measured inflow by 1.5–2× for a safety factor and storm headroom. This measured design flow, not a guess, is what you take to the pump curve — undersizing here is the most common reason a 'big enough' pump still floods.