Pool Fill Time Calculator
Planning a Fill Before It Becomes an All-Night Job
Filling a drained pool, or topping off after significant evaporation, is a simple division problem — but the answer surprises people who assume a garden hose fills a pool in an afternoon. A typical hose delivers somewhere between 9 and 12 GPM, meaning a mid-size residential pool can take well over a day of continuous running. Knowing the fill time in advance lets you plan around it rather than checking on it every hour.
The Formula
The result is converted from total minutes into hours and minutes for a more useful readout.
Fill Time by Flow Rate
| Flow rate | Fill time |
|---|---|
| 10 GPM (typical garden hose) | 33 hr 20 min |
| 15 GPM (higher-flow hose) | 22 hr 13 min |
| 20 GPM (dedicated fill line) | 16 hr 40 min |
Doubling the flow rate doesn't exactly halve the fill time in these examples because the rates aren't exact multiples of each other, but the relationship is inverse: fill time is always volume divided by flow rate, so a faster source always shortens the job proportionally.
Where This Calculation Matters
- Post-drain refills — after acid washing, resurfacing, or winterization, knowing the fill duration helps schedule when chemical balancing and pump startup can begin.
- Water bill and utility planning — a multi-day fill running a garden hose continuously has a real cost, worth estimating before starting.
- Choosing a fill method — comparing a standard hose against a rented high-flow fill service shows exactly how much time a faster option would actually save.
How to Use This Calculator
- Enter your pool volume in gallons.
- Enter your water source's flow rate in gallons per minute (GPM).
- Select Calculate to see the estimated fill time in hours and minutes.
Related Calculations
If you need an accurate gallon figure first, use the Pool Volume Calculator, or check the Pool Water Evaporation Calculator to estimate ongoing top-off needs after the initial fill.