Pool Fill Time Calculator
Find out how long it takes to fill your pool using your hose flow rate and pool volume. Get a realistic time estimate in seconds.
Calculate your fill time
Use your pool's known gallons, or estimate volume from its dimensions.
About 1 day, 7 hours, 15 minutes
How to use the pool fill time calculator
1. Enter pool volume
Use the known water volume from your pool documentation, or select dimensions to estimate gallons from shape and average depth.
2. Measure hose flow
Time how long it takes to fill a 5-gallon bucket. Divide 300 by the elapsed seconds to get gallons per minute.
3. Choose how much to add
Set 100% for an empty pool or a smaller percentage for a partial refill. The result updates automatically as you type.
Pool fill time formula
Fill time (minutes) = Gallons to add ÷ Hose flow (gallons per minute). To convert minutes into hours, divide by 60. For example, 15,000 ÷ 8 = 1,875 minutes = 31 hours and 15 minutes.
For a rectangular pool, estimated gallons = length (ft) × width (ft) × average depth (ft) × 7.48052. For a round pool, the calculator uses π × (diameter ÷ 2)² × depth × 7.48052. For an oval, it uses π × (length ÷ 2) × (width ÷ 2) × depth × 7.48052. These are geometric estimates; steps, benches, curved walls and irregular depths change actual capacity.
How long does it take to fill a pool?
| Pool volume | 5 GPM | 8 GPM | 12 GPM |
|---|---|---|---|
| 5,000 gallons | 16 hr 40 min | 10 hr 25 min | 6 hr 57 min |
| 10,000 gallons | 33 hr 20 min | 20 hr 50 min | 13 hr 53 min |
| 15,000 gallons | 50 hr | 31 hr 15 min | 20 hr 50 min |
| 20,000 gallons | 66 hr 40 min | 41 hr 40 min | 27 hr 47 min |
Examples assume steady hose flow, a fully empty pool and no interruptions. Times rounded to the nearest minute.
What affects your actual fill time?
Hose flow depends on supply pressure, hose length and diameter, fittings, other fixtures using water, and local restrictions. A published hose rating is not the same as the flow measured at your property. A 5-gallon bucket test is a practical starting point: if the bucket fills in 40 seconds, the measured flow is 7.5 GPM.
Measure hose flow accurately with a bucket
A pool-fill estimate is only as reliable as the flow rate. Instead of guessing from the hose label, measure water delivery at the actual spigot and hose setup you plan to use. A longer hose, partially closed valve, splitter, or other household water use can change the result.
Step 1 · Set up
Use the same spigot, hose, nozzle setting and valve position you'll use for the pool. Put a clearly marked five-gallon bucket on stable ground.
Step 2 · Time it
Start a stopwatch when the bucket begins filling and stop at the five-gallon mark. Repeat the test twice and average the seconds for a more useful estimate.
Step 3 · Convert
For a five-gallon bucket, GPM = 300 ÷ seconds. A 30-second fill is 10 GPM; a 60-second fill is 5 GPM. Enter your result above.
Estimating pool gallons from dimensions
If you don't know your pool's water capacity, select the dimensions tab in the calculator. Measure in feet, and use the average water depth rather than the deepest point. For a pool that slopes from 3 to 7 feet, a simple average is 5 feet; unusual floors may require a more detailed volume estimate.
| Pool shape | Approximate formula (cubic feet) | What to measure |
|---|---|---|
| Rectangular | Length × width × average depth | Inside water dimensions, not deck dimensions |
| Round | π × (diameter ÷ 2)² × average depth | Inside diameter at waterline |
| Oval / elliptical | π × (length ÷ 2) × (width ÷ 2) × average depth | Inside length and width at waterline |
Multiply cubic feet by approximately 7.48052 to estimate US gallons. Freeform pools, large steps, tanning ledges, spas, and sloped walls need more careful measurement; the shapes above are simplified geometric models.
Partial refills versus filling an empty pool
If you're replacing only part of the water, enter the percentage that needs to be added. For example, refilling 25% of a 16,000-gallon pool means adding about 4,000 gallons. At a measured 8 GPM, that's roughly 8 hours 20 minutes. The percentage option is an estimate: for a water-level top-off, a measured change in inches and pool surface area can be more accurate.
Estimate water use and cost
The calculator reports gallons to add, which you can use with your utility's current water tariff. For a rough estimate, multiply gallons by the combined applicable rate per 1,000 gallons and divide by 1,000. For example, 15,000 gallons at $6 per 1,000 gallons would be about $90 before any fixed fees, wastewater charges, tiered pricing or other adjustments. Local billing rules vary; some utilities offer separate pool-fill or sewer-adjustment procedures.
Filling precautions and planning checklist
- Check local water-use restrictions and whether a fill notification is required.
- For a newly built, replastered, vinyl-lined or fiberglass pool, follow the builder's specific filling instructions; some finishes require continuous filling or other precautions.
- Keep the hose outlet positioned to avoid disturbing a new finish or creating a siphon risk; follow local backflow-prevention rules.
- Plan for changing pressure and interruptions. Recheck the water level frequently and never leave filling unattended.
- Once filled, test and balance the water according to your pool's surface, sanitizer system and manufacturer guidance.
Why your real fill time may differ
Flow slows down
Other fixtures, irrigation, a shared water supply or changing municipal pressure can reduce hose flow. Retest the bucket rate during the fill if the estimate seems off.
Gallons were overstated
Using maximum rather than average depth, including deck dimensions or ignoring steps can inflate the pool volume estimate.
Multiple hoses
Measure combined output rather than simply doubling one hose's GPM. Two hoses on the same supply may reduce pressure and each other's flow.
Frequently asked questions
How do I find my garden hose flow rate?
Fill a bucket of known size and measure the time in seconds. Flow in GPM = bucket gallons × 60 ÷ seconds. Repeat the test and average the results for a better estimate.
Can I use two hoses to fill a pool faster?
Yes, if the water supply supports both. Measure the combined output, since two hoses sharing a supply may not deliver twice the flow of one hose.
Does the calculator work for above-ground pools?
Yes. Enter the pool's stated capacity or estimate volume using the appropriate shape and average water depth. Use actual water depth rather than wall height.
How long does a 15,000-gallon pool take to fill?
At a constant 8 GPM, about 31 hours and 15 minutes. At 12 GPM, about 20 hours and 50 minutes. Your measured flow determines the actual estimate.
Can I use two garden hoses to fill a pool faster?
Often yes, but the total flow may be less than twice the single-hose flow if both share the same supply. Measure the combined output or each hose while both are running, then enter their combined GPM.
Does hose diameter change the fill time?
It can. A wider or shorter hose may reduce flow restriction, but actual delivery also depends on spigot pressure, fittings and the plumbing supply. Measure at the outlet for the most useful estimate.
Should I use the pool's total capacity for a top-off?
No. Estimate only the missing water. Use the partial-fill percentage or calculate the missing water level using pool surface area.
Why is my estimated time different from the actual time?
Flow may vary during the day, and pool volume is often approximate. Bucket-test the hose again, check the actual fill level, and allow for interruptions.
Related calculators and guides
Use these tools for the next steps in pool setup and water care. Each serves a different purpose; none replaces measuring your hose flow.
For a more precise volume estimate, use the pool volume calculator. After filling, the turnover time calculator helps estimate circulation duration. This tool provides estimates for planning, not a guarantee of fill time or water use. All gallons are US liquid gallons. No purchase is necessary to use the calculator.