Pool Pump Run Time Calculator
Your real run time from your pool and your pump — not the generic “8 hours.” With the two physics truths the rule of thumb misses: one turnover only filters ~63 %, and pump power scales with the cube of speed. That second fact alone is why slow-and-long beats fast-and-short by a factor of four.
Hook
Ask the internet how long to run your pool pump and you'll get “8 hours a day.”
It's a one-size answer that ignores your pool, your pump, and the single most important fact about pumps: the power they draw rises with the cube of their speed. Run your pump at half speed and it sips about an eighth of the power. The catch — and the opportunity — is that slow circulation is dramatically cheaper than fast, and most people are running their pump too hard, too short, and paying for it.
Promise
This calculator works out your real pump run time from your pool volume and your pump's flow rate — how long for a full turnover, how many turnovers you actually need, and what the variable-speed payoff looks like. It shows the truth about turnover (one pass doesn't clean the whole pool — it's exponential), and it shows the cube-law math behind why slow-and-long beats fast-and-short. Every term derived on the page.
Here's the deal: filtering a pool is about moving its water through the filter enough times to keep it clear — that's turnover. But the water you return mixes back in, so turnover is exponential, not a clean sweep. And because pump power scales with the cube of flow, the cheapest way to get your turnovers is slowly. Run time isn't a fixed number — it's a trade between flow rate, turnovers, and the electric bill.
What you'll give us
Your pool volume and your pump's flow rate. Volume comes from the Phase-1 pool volume calculator — deep-link from there with ?gal= prefilled. Pick single-speed or variable-speed for your pump type; variable-speed unlocks the speed slider and the cube-law savings.
The calculator
Pick a mode — RUN TIME (the classic “how long?”) or REQUIRED FLOW (the reverse, used when sizing a pump) — fill the fields, hit Calculate. The result panel shows the turnover time, what each turnover actually filters (1 − e⁻ⁿ), and the variable-speed cube-law payoff at your chosen speed.
What “turnover” actually means
“Turnover” sounds like it should mean your whole pool gets cleaned in one pass — pump the volume through the filter once, done. It doesn't work that way. The filtered water you return to the pool immediately mixes with the dirty water, so the next gallon the pump pulls is a blend.
Filtration is exponential. After one full turnover, only about 63 % of your water has actually been through the filter. You need about three turnovers to get to 95 %. That's why “one turnover a day” is a floor, not a guarantee of a spotless pool — and why how clean your water looks depends on more than just hours.
The cube law: why slow is cheap
Here's the fact that should change how you run your pump. A pump's power draw doesn't rise in step with its speed — it rises with the cubeof it. Run your pump at half speed and it doesn't use half the power; it uses about an eighth.
Now, at half speed it moves water half as fast, so a turnover takes twice as long — but do the arithmetic: an eighth the power for twice the time is a quarter of the energy. The same turnover, for a quarter of the cost. That's not a small saving; that's the entire reason variable-speed pumps exist.
One honesty note: the “quarter of the energy” figure is the textbook idealization. Real pipe friction follows a slightly different exponent, and real systems have static head (gravity lift) that doesn't scale with flow — the pump-cost calculator works the saving out for your actual system; for a typical pool it's closer to 60 % saving than 75 %. Still one of the best returns in pool ownership.
How long should YOU run it?
So what's your number? Start with your pool volume and your pump's flow rate — that gives your turnover time. Aim for the equivalent of one turnover a day as a baseline, more in heavy use or hot weather, and remember you don't need to do it all at once or all at full speed.
If you have a variable-speed pump, the cheapest path is to run it slow for more hours — same turnover, far less energy. If you have a single-speed pump, you're stuck at its one flow, so you're trading only hours, not speed. And honestly: most pools with good chemistry stay clear at one turnover or less — so if your water's clear, you're probably running the pump longer than you need.
When to run it
Two timing questions beyond “how long”: when in the day, and split or continuous. For a chlorine pool, running during daylight helps circulate sanitizer when the sun is burning it off fastest, and a single longer block beats many short ones for actually achieving turnover.
But if your electricity is cheaper at night, a variable-speed pump run slow overnight can be both adequate and cheap. There's no single right answer — it's your rates, your pool, your pump.
Where the numbers come from
The filtration cluster's engine root: the lib/hydraulics/flow.ts module, the fluid-dynamics parallel to lib/dosing/ (chemistry) and lib/thermal/ (thermodynamics).
Step 1 · turnover = volume ÷ flow rate
turnoverHours = volumeGal / (pumpGpm × 60). The volume comes from the pool volume calculator —volumeToGalimported from the chemistry cluster'slib/dosing/core.ts, one source of gallons across chemistry, heating, and hydraulics. For a 20,000-gal pool with a 60 GPM pump: 20,000 ÷ (60 × 60) = 5.56 hours per turnover.Step 2 · required flow (the inverse — REQUIRED FLOW mode)
Pure algebraic inversion:
requiredGpm = volumeGal / (turnoverHours × 60). For the same 20k pool with an 8-hour target: 41.7 GPM. This is the input the pump-sizing calculator starts from.Step 3 · exponential mixing — EXACT physics
Treat the pool as a continuous-stirred-tank (CSTR): clean returned water mixes instantly with the dirty bulk, so each pump-pull draws a blend.
fractionFiltered(n) = 1 − e⁻ⁿ.Turnovers Filtered 1 63.21 % 2 86.47 % 3 95.02 % 4 98.17 % The integrity wedge: every clone calculator treats one turnover as a clean sweep. It isn't — it's ~63 %. Labeled EXACT physics, locked in the assertion.
Step 4 · the affinity laws — EXACT physics
Centrifugal-pump affinity relation:
power / rated = (flow / rated)^3. Power scales with the CUBE of flow. Derivation: continuity (mass flow ∝ speed) combined with Euler turbomachinery (head ∝ speed²) gives power = mass-flow × head ∝ speed³. At half flow: power = 0.5³ = 0.125 = 12.5 % of rated.Energy per turnover follows by composition:
energy = power × time = flow³ × (1 / flow) = flow^2. At half flow: 0.5² = 0.250 = 25 % of rated energy for the same turnover. The variable-speed payoff in one line.Step 5 · the honesty split
The turnover targets(8 hours, 1 turnover per day) are CONVENTIONS — research §3 / §12 / F3. Bather load, debris, temperature, and chlorination shift what's adequate. Present them as a baseline; don't dogmatically prescribe.
The physics (exponential mixing, cube law) is EXACT and labeled so. The numbers above are not engineering estimates — they're derivations from first principles, locked in
assert-hydraulics.mjsso they can't silently degrade.
Eight worked examples
All numbers consume the asserted lib/hydraulics/flow.ts engine — the physics is exact; the targets are conventions.
E1 — How long to run a standard pump (the core case)
20,000 gal pool, 60 GPM pump → one turnover = 20,000 ÷ (60 × 60) ≈ 5.6 hours. A daily-turnover baseline is ~5.6 hr — not the reflexive “8.”
Takeaway: your pump may turn the pool over faster than the rule of thumb assumes — match the hours to your actual flow, not a generic number.
E2 — Required flow for an 8-hour turnover (REQUIRED FLOW mode)
20,000 gal, target 8-hr turnover → ≈ 41.7 GPM needed.
Takeaway:if you're sizing a pump, this is the flow you're aiming for — and it's the number the pump-sizing calculator starts from.
E3 — The exponential-mixing truth (the integrity wedge)
After 1, 2, 3, 4 turnovers: 63 %, 86 %, 95 %, 98 % of the water has passed the filter (= 1 − e⁻ⁿ).
Takeaway:one turnover doesn't clean your whole pool — it filters about two-thirds of it. For genuinely clear water you're looking at two to three turnovers, which reframes what “enough” means.
E4 — The cube law: half speed, quarter cost (the flagship wedge)
Variable-speed pump at 100 % vs 50 % flow → 50 % flow draws 12.5 % of the power; the turnover takes 2× longer, so the same turnover uses 25.0 % of the energy (12.5 % power × 2× time = 25 % energy).
Takeaway: running your variable-speed pump at half speed for twice as long does the same job for a quarter of the electricity. This single fact pays off the pump.
E5 — Three speeds compared (the affinity gradient)
Same turnover target at 100 % / 75 % / 50 % flow: 100 % = full power, baseline energy; 75 % = 42.2 % power, 56.3 % energy; 50 % = 12.5 % power, 25.0 % energy.
Takeaway:every notch slower is disproportionately cheaper — the savings aren't linear, they're cubic. Slow as you can while keeping the water clear.
E6 — Required flow by pool size (the sizing reference)
- 10,000 gal → 20.8 GPM
- 15,000 gal → 31.3 GPM
- 20,000 gal → 41.7 GPM
- 30,000 gal → 62.5 GPM
Takeaway: bigger pools need proportionally more flow for the same turnover — the starting point for sizing a pump.
E7 — “Run it less than you think” (the honest reframe)
A well-chlorinated 20k pool with a 60 GPM pump: the reflexive 8-hour run gives 1.44 turnovers (≈ 76 % filtered) — but adequate filtration with good chemistry often needs ~1 turnover, ~5.6 hr. Most owners over-run their pumps; the physics says you can usually run less (or slower), not more.
Takeaway:if your water's clear and your chemistry's good, you're probably running the pump longer than you need — and definitely faster than you need.
E8 — Metric
75 m³ (≈ 19813 gal) pool with a 13 m³/hr pump (≈ 57.2 GPM) → turnover ≈ 5.77 hours.
Takeaway: the turnover math is identical in metric — volume over flow.
Reference tables
T1 · Required flow & turnover time by pool size
CONVENTION + computed · required GPM for an 8-hr turnover (convention), and the turnover time a typical 60 GPM pump delivers (computed). The 8-hr target is a guideline, not a law.
| Pool (gal) | Required GPM (8-hr) | Turnover @ 60 GPM |
|---|---|---|
| 10,000 | 20.8 | 2.78 hr |
| 12,000 | 25.0 | 3.33 hr |
| 15,000 | 31.3 | 4.17 hr |
| 18,000 | 37.5 | 5.00 hr |
| 20,000 | 41.7 | 5.56 hr |
| 25,000 | 52.1 | 6.94 hr |
| 30,000 | 62.5 | 8.33 hr |
| 40,000 | 83.3 | 11.11 hr |
T2 · Exponential filtration (the integrity wedge)
EXACT physics · 1 − e⁻ⁿ. The dataset that corrects the “one turnover = 100 % filtered” near-universal misconception.
| Turnovers | Fraction filtered |
|---|---|
| 0.5 | 39.35 % |
| 1 | 63.21 % |
| 1.5 | 77.69 % |
| 2 | 86.47 % |
| 2.5 | 91.79 % |
| 3 | 95.02 % |
| 4 | 98.17 % |
T3 · Affinity-law energy (the cube-law wedge)
EXACT physics · power ∝ flow³, energy-per-turnover ∝ flow². The variable-speed savings as a dataset.
| Flow (% rated) | Power (% rated) | Energy / turnover (% rated) |
|---|---|---|
| 100 % | 100.0 % | 100.0 % |
| 90 % | 72.9 % | 81.0 % |
| 80 % | 51.2 % | 64.0 % |
| 75 % | 42.2 % | 56.3 % |
| 66 % | 28.7 % | 43.6 % |
| 50 % | 12.5 % | 25.0 % |
| 33 % | 3.6 % | 10.9 % |
Tables released CC BY 4.0. T2 and T3 are exact physics; T1 turnover targets are conventions.
Methodology & sources
Turnover = volume ÷ flow rate. Fluid dynamics. The volume input comes from the pool volume calculator — volumeToGal imported from the chemistry cluster's lib/dosing/core.ts. One source of gallons across chemistry, heating, and hydraulics — the calculators can't disagree about what your pool is.
Exponential filtration (F4).The pool is modelled as a continuous-stirred-tank reactor: clean returned water mixes instantly with the dirty bulk, so each pump-pull draws a blend. The closed-form solution is fraction filtered = 1 − e⁻ⁿ, where n is the number of turnovers. This is exact physics — the same model used in chemical-reactor engineering for residence-time distributions. Anchors: 1 turnover → 63 %, 2 → 86 %, 3 → 95 %, 4 → 98 %. The integrity wedge: most pool-pump calculators silently assume one turnover cleans 100 % of the water; it doesn't.
The pump affinity laws (F5–F7).Standard centrifugal-pump relations: power ∝ flow³ (or equivalently speed³), derived from continuity (mass flow ∝ speed) combined with Euler turbomachinery (head ∝ speed²). Energy per turnover follows: energy = power × time = flow³ × 1/flow = flow². At half speed the same turnover takes 2× the hours but costs 25 % of the energy — the entire reason variable-speed pumps exist. These are exact physical laws, not engineering estimates; they're labelled EXACT in the result panel and locked in the assertion.
State plainly: the turnover targets are CONVENTIONS, not laws.The “8 hours / 1 turnover per day” rule of thumb is a baseline — actual circulation needs vary with bather load, debris, temperature, and chlorination method. The honest conclusion is that most pools with good chemistry can run less than 8 hours, and a variable-speed pump can run substantially slower. We don't prescribe a single number; we show the turnover math and what each turnover actually filters. F3, F9, §12.
Circulation is not sanitation. The pump moves water through the filter; chlorine sanitizes the water. Running the pump longer doesn't replace adequate chemistry — see the chlorine, pH, and LSI calculators for those. F7 / §12 #7.
No pump-brand advocacy.Single-speed vs variable-speed is physics (F12), not a sales pitch. A single-speed pump runs at one (high) flow, so it can't trade speed for energy — it can only trade hours. A variable-speed pump unlocks the cube-law savings because its speed is genuinely variable. The trade-off is presented straight; no affiliate funnels.
Where this engine plugs in. The required-flow output (REQUIRED FLOW mode) feeds the pump-sizing calculator — the fluid-dynamics flagship that adds lib/hydraulics/headloss.ts (pipe friction, fittings, filter ΔP → system curve) and lib/hydraulics/pumpcurve.ts (manufacturer head-vs-flow → operating-point intersection). The affinity-law energy figures here feed the pump-running-cost calculator which reuses lib/thermal/fuelcost.ts's electricity rate — the filtration cluster reaches into the heating cluster's fuel-cost layer the same way this page reaches into the chemistry cluster's volume engine. The portfolio compounds.
Tables T1/T2/T3 released under CC BY 4.0. T2 and T3 are exact physics; T1 turnover targets are conventions, labeled accordingly.
Frequently asked questions
- How long should I run my pool pump?
Aim for the equivalent of one turnover a day as a baseline. Compute it from your pool volume and pump flow rate: hours = volume ÷ (GPM × 60). For a 20,000-gal pool with a 60 GPM pump, that's about 5.6 hours — not the reflexive 8. The conventional 8-hr target is a guideline, not a law; most pools with good chemistry can run less.
- Does one turnover clean the whole pool?
No — it filters about 63 %. Filtered water mixes back with dirty water, so circulation is exponential, not a clean sweep. Two turnovers reach about 86 % filtered, three reach 95 %. That's why one turnover a day is a floor, not a guarantee of pristine water — clarity also depends on chemistry, debris load, and bather use.
- Should I run my pool pump 24/7?
Usually no. The conventional one-turnover-a-day target gets you about 63 % filtered, and most residential pools with adequate chlorine stay clear at that. Running 24/7 is wasteful, especially with a single-speed pump. With a variable-speed pump you can run longer at lower speed for the same turnover and much less energy — the cube law makes slow-and-moderate dramatically cheaper than fast-and-short.
- Why is a variable-speed pump cheaper to run?
Pump power scales with the cube of flow. Run a variable-speed pump at half speed and it draws about an eighth of the power. The turnover takes twice as long — but an eighth power for twice the time is a quarter of the energy. Same job, quarter the cost. That ratio is the entire reason variable-speed pumps exist. Honestly: the textbook 75 % is idealized; real systems with static head and real Hazen-Williams pipe friction land closer to 60 %. The pump-cost calculator works it out for your actual pool.
- How many turnovers a day do I need?
One turnover is the convention; that filters about 63 % of the water on each pass. Most pools with adequate chlorine stay clear at one turnover. Two turnovers reach 86 %, three reach 95 %. For heavy bather load, hot weather, or after a shock event, run two; otherwise one is usually plenty— and well under “all day.”
- What flow rate do I need for my pool?
For an 8-hour turnover: 10k pool ≈ 21 GPM, 15k ≈ 31, 20k ≈ 42, 30k ≈ 63. Formula: required GPM = volume ÷ (turnover hours × 60). Switch the calculator to REQUIRED FLOW mode and enter your volume and target turnover — the result is the flow rate the pump-sizing calculator starts from.
- Is it better to run the pump at night or during the day?
It depends. For a chlorine pool, running during daylight circulates fresh sanitizer when the sun burns chlorine fastest. But if your electricity is cheaper at night (off-peak rates), a variable-speed pump run slow overnight can be both adequate and dramatically cheaper. One longer block beats many short ones either way — short cycles waste startup current and rarely finish a turnover.
- Can I save money with my existing single-speed pump?
Limited. A single-speed pump runs at one (high) flow — you can save by running fewer hours, but each hour costs the same. The dramatic slow-and-long savings need a variable-speed pump because they come from running at lower speed, not just shorter hours. If you're running well above one turnover a day on single-speed, cutting back to one turnover is the main lever available.
Related calculators
Next in Pool Pump & Filter: Pool Pump Size Calculator.
Related across clusters: Pool Chlorine Calculator.
All Pool Pump & Filter calculators: browse the hub.