How to use the pool fill time calculator
- Enter the amount of water to add — the whole pool volume for a fill, or just a top-up.
- Choose your water source: a hose size estimate, a bucket test, or a flow rate you know.
- Enter the number of hoses running at once.
- Add your water price from the bill to see the cost.
The formulas
Flow (gpm) = Bucket gallons ÷ Seconds × 60 Total flow = Flow per hose × Number of hoses Fill time (h) = Gallons ÷ Total flow (gpm) ÷ 60 Cost = Gallons ÷ 1,000 × Price per 1,000 gal (or ÷ 748 × Price per CCF)
Worked example
A 20,000 gallon pool and a hose that fills a 5-gallon bucket in 30 seconds:
- Flow = 5 ÷ 30 × 60 = 10 gpm
- Time = 20,000 ÷ 10 ÷ 60 = 33.3 hours (about 1 day 9 hours)
- With two hoses on separate supplies: about 16.7 hours
- At $5 per 1,000 gallons, the water costs about $100
Fill time by pool size and flow
| Pool | 8 gpm | 12 gpm | 17 gpm |
|---|---|---|---|
| Hot tub, 400 gal | 50 min | 33 min | 24 min |
| Above-ground 15 ft round, 4,500 gal | 9.4 h | 6.3 h | 4.4 h |
| Above-ground 24 ft round, 12,000 gal | 25 h | 16.7 h | 11.8 h |
| In-ground 16 × 32 ft, 20,000 gal | 41.7 h | 27.8 h | 19.6 h |
| In-ground 20 × 40 ft, 32,000 gal | 66.7 h | 44.4 h | 31.4 h |
What affects hose flow
- Water pressure: most homes have 40–60 psi; higher pressure means more flow.
- Hose diameter: a ¾ in hose carries far more than a ½ in hose.
- Hose length: a 100 ft hose flows noticeably less than a 25 ft hose.
- Spigot and fittings: nozzles, splitters and timers restrict flow — remove them while filling.
- Other water use: showers, irrigation and laundry at the same time reduce what reaches the pool.
Tips for filling a pool
- Call your water utility: some offer a sewer-charge credit for pool fills, and some areas have watering restrictions.
- Don’t leave it unattended for long overnight without a timer or alarm — overflowing wastes water and money.
- Vinyl liners: fill slowly at first and smooth out wrinkles while the water is just a few inches deep.
- Well water: check your well’s recovery rate; running it for a day or more can draw it down. Test for iron and copper.
- Balance after filling: test pH, alkalinity, calcium hardness and chlorine, then add stabilizer if the pool is outdoors.
For a hot tub, fill through the filter compartment so air is pushed out of the plumbing and the pumps don’t run dry.