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Pump Drain Time Calculator

Hours to drain a pool, flooded basement or tank — from the pump's real operating point on its hose, not the zero-head number on the box.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-28 · v1.0.0

Market
Imperial · sales tax
33 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Estimated drain time

10.4 hours

Check your inputs

Built on a linearised pump curve and Hazen–Williams hose friction (C = 150). A manufacturer's published curve, where you have one, governs.

Delivered flow at the operating point
21.14 gal/min
Share of rated flow surviving lift and hose
39.88 %
Friction head in the hose
9.13 ft
Total dynamic head
15.63 ft

At the values currently entered, the estimated drain time works out to 10.4 hours. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown in United States units and terminology; switch the market above if you are building elsewhere.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • Hazen–Williams empirical head-loss formula, h_f = 10.67·L·Q^1.852 / (C^1.852·d^4.87), with C = 150 for smooth plastic/rubber hose — standard engineering hydraulics form (SI units)
  • Pump performance approximated as a linear curve from rated flow at zero head to zero flow at rated maximum head — the standard first approximation for small utility and submersible pumps; the manufacturer's published curve governs where one exists

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why is the drain time so much longer than volume ÷ rated flow?
The rated flow is measured at zero head — pump sitting in water, no hose, no lift. Real jobs have both, and the pump slides down its curve until the head it can still produce matches what the lift and the hose friction demand. That operating point, not the box number, sets the time.
What helps more: a bigger pump or a bigger hose?
Usually the hose. Friction loss grows with almost the fifth power of shrinking bore, so stepping a 25 mm hose up to 38 mm cuts friction to roughly a seventh. A bigger pump pushed through the same narrow hose spends most of its extra power making friction.
The result says 0 hours. Is the pool already empty?
No — 0 here means never. Your vertical lift meets or exceeds the pump's maximum head, so no water arrives at the outlet. The confidence note says so when it happens.
Does the last few centimetres of water drain at the same rate?
No. As the level drops the lift grows slightly, and most pumps also lose prime in very shallow water. The final draw-down is slower than this average, and utility pumps typically leave a few millimetres behind.