Pool Fill Time Calculator
Select your pool shape above to enter dimensions.
How Long Does It Take to Fill a Pool?
For most homeowners filling with a standard garden hose, expect somewhere between 12 and 48 hours depending on pool size and water pressure. The exact time comes down to two numbers: how many gallons your pool holds and how fast water comes out of the hose in gallons per minute (GPM).
The formula: Gallons to add ÷ GPM = minutes to fill
A 15,000-gallon pool with a typical 9 GPM hose takes 15,000 ÷ 9 = 1,667 minutes, or about 27.8 hours. Use the calculator above and it works it out automatically along with a finish time based on when you plan to start.
How to Measure Your Actual Hose GPM
The GPM number matters more than anything else in this calculation. A hose that moves 9 GPM takes 40% longer than one doing 15 GPM. These are not exotic differences – normal variation between homes, hose lengths, and water pressure.
The bucket test takes 30 seconds and is far more accurate than guessing:
- Get a 5-gallon bucket and your phone.
- Turn the hose on full blast and time how many seconds it takes to fill the bucket.
- Divide 300 by those seconds. That is your GPM.
Examples: 25 seconds = 12 GPM. 38 seconds = 7.9 GPM. 50 seconds = 6 GPM.
Garden Hose GPM by Hose Type
| Hose type | Typical GPM | Gallons per hour |
|---|---|---|
| 1/2 inch hose, 100 ft, low pressure | 3 to 5 GPM | 180 to 300 gal/hr |
| 5/8 inch hose, 50 ft (most common) | 8 to 12 GPM | 480 to 720 gal/hr |
| 5/8 inch hose, 25 ft, high pressure | 12 to 17 GPM | 720 to 1,020 gal/hr |
| 3/4 inch hose, 50 ft | 14 to 20 GPM | 840 to 1,200 gal/hr |
| Two 5/8 inch hoses (2 separate spigots) | 16 to 24 GPM | 960 to 1,440 gal/hr |
How Long to Fill a Pool by Size
| Pool size | Approx gallons | 1 hose (9 GPM) | 2 hoses (18 GPM) | Water truck |
|---|---|---|---|---|
| 10 ft round, 30 in deep | ~1,500 gal | ~2.8 hrs | ~1.4 hrs | 1 load |
| 15 ft round, 4 ft deep | ~5,300 gal | ~9.8 hrs | ~4.9 hrs | 1 load |
| 18 ft round, 4 ft deep | ~7,600 gal | ~14 hrs | ~7 hrs | 1 load |
| 24 ft round, 4.5 ft deep | ~15,200 gal | ~28 hrs | ~14 hrs | 2 loads |
| 12 x 24 ft, 4.5 ft avg depth | ~9,700 gal | ~18 hrs | ~9 hrs | 2 loads |
| 16 x 32 ft, 5 ft avg depth | ~19,200 gal | ~35.5 hrs | ~17.8 hrs | 3 loads |
| 18 x 36 ft, 5.5 ft avg depth | ~26,600 gal | ~49 hrs | ~24.5 hrs | 4 loads |
| 20 x 40 ft, 5.5 ft avg depth | ~32,800 gal | ~60.7 hrs | ~30.4 hrs | 5 loads |
How to Fill a Pool Faster
Use a wider or shorter hose
A 3/4 inch garden hose delivers close to double the water of a standard 5/8 inch hose at the same pressure. Every extra 50 feet of hose length also loses you 10 to 15% of flow due to friction. Only use as much hose as you actually need.
Use two hoses from two separate spigots
Connect a second hose to a different outdoor tap, not a Y-splitter on the same spigot. A splitter just divides the same supply in two and you get no benefit. Two separate taps mean two separate water supplies – you genuinely double the flow rate.
Fill at night or before sunrise
City water pressure drops during peak hours – 7 to 9am and 6 to 9pm when everyone is showering and running dishwashers. Start filling at 10pm or before 6am and you will get noticeably better pressure. As a bonus, water sitting in a black garden hose in direct sun can get quite hot and deposit minerals on your pool surface, so overnight filling sidesteps that problem too.
Get a pool fill pre-filter
A hose-end pre-filter clips on between the spigot and the hose. It catches iron, copper, and sediment before any of it gets into the pool. It won’t make filling faster but it will save you from brown stains and hundreds of dollars in metal treatment chemicals. If you have well water or live in an older house, this is not optional. Attach it at the spigot end.
Hire a water delivery truck
A professional water truck fills a pool in 2 to 6 hours total. Loads run 5,000 to 10,000 gallons each. Expect $175 to $380 per truckload depending on where you live. For a 20,000-gallon pool you need 2 to 4 loads. Yes, it costs more than tap water, but you won’t spend two days babysitting a hose.
What to Do While the Pool Fills
Don’t treat filling a pool like putting a kettle on.
Check it every 2 to 3 hours
Hoses slip out, kink, or lose pressure without warning. An overflow can dump thousands of gallons onto your lawn or driveway. Set a phone alarm every 2 to 3 hours.
Add a stain preventer at 25% full
Once the pool is a quarter full, add a stain and scale preventer. Tap water carries minerals and metals that will deposit on the surface the moment chlorine touches them. Getting the preventer in early stops that before it starts.
Turn the pump on at 50% full
Once the water reaches the skimmer opening, around the halfway point, you can turn the pump on briefly. It helps circulate any chemicals you’ve added. Never run the pump before water covers the skimmer intake or you’ll burn out the seal.
Check your water meter
Write down your meter reading before you turn the hose on, then check it again after an hour. Subtract the two numbers to get your exact gallons per hour. That gives you a much more accurate finish time than any estimate.
How Much Does It Cost to Fill a Pool?
Water is billed per 1,000 gallons. The US average sits around $3.50 to $6.50 per 1,000 gallons. Find your exact rate on your water bill.
Water cost = Gallons ÷ 1,000 x Rate per 1,000 gallons
Example: 20,000 gallon pool at $5.00 per 1,000 gallons = 20 x $5.00 = $100.
| Pool volume | Cost at $4/1K gal | Cost at $6/1K gal |
|---|---|---|
| 5,000 gallons | ~$20 | ~$30 |
| 10,000 gallons | ~$40 | ~$60 |
| 15,000 gallons | ~$60 | ~$90 |
| 20,000 gallons | ~$80 | ~$120 |
| 30,000 gallons | ~$120 | ~$180 |
Filling With Well Water
If your home is on well water, filling a pool requires more planning than city water:
- Check your well’s recovery rate first. If the well can’t sustain the draw it will run dry mid-fill, which can damage the pump. You want at least 600 gallons per hour (10 GPM) before you start.
- Test for iron and copper. Well water commonly carries both. The moment chlorine touches those metals, you get brown or green stains that are a nightmare to remove. Use a hose-end pre-filter and add a metal sequestrant before adding any chlorine.
- Fill in stages. Run the pump for 2 to 4 hours, then let the well recover for an hour before running it again. This keeps the pump from running dry.
- Seriously consider a water delivery truck to fill most of the pool, then use your well to top up only.
What to Do After the Pool Is Full
A full pool is not a swim-ready pool. Fresh tap water is not balanced and is not safe to swim in yet. Do it in this order:
- Test the water. Use a test kit or test strips to check pH, total alkalinity, calcium hardness, and cyanuric acid.
- Adjust total alkalinity first – target 80 to 120 ppm. Add baking soda to raise it.
- Adjust pH – target 7.2 to 7.6. Soda ash to raise, muriatic acid to lower.
- Shock the pool with pool shock to kill bacteria in fresh water. About 2 lbs of cal-hypo per 10,000 gallons.
- Add cyanuric acid for outdoor pools – target 30 to 50 ppm.
- Wait 24 to 48 hours with the pump running. Re-test before letting anyone in.
Frequently Asked Questions
How long does it take to fill a pool with a garden hose?
With a typical garden hose at 9 GPM, a 10,000-gallon pool takes about 18.5 hours. A 20,000-gallon pool takes about 37 hours. Two hoses roughly halves the time. Use the calculator above with your actual hose speed for a precise number.
How long to fill a 10,000-gallon pool?
At 9 GPM, about 18 to 19 hours with one garden hose. About 9 to 10 hours with two hoses from separate spigots.
How long to fill a 15,000-gallon pool?
At 9 GPM, about 27 to 28 hours with one hose. With two hoses at 18 GPM combined, about 14 hours.
How long to fill a 20,000-gallon pool?
About 37 hours with one garden hose at 9 GPM. About 18.5 hours with two hoses. A professional water truck (2 to 3 loads) can do it in 4 to 8 hours.
Can I leave the hose running overnight?
Yes, and overnight is actually the better option because pressure is higher when fewer people are using water. Set a phone alarm to check it every few hours. Hoses slip out and a pool overflow is a serious mess.
How much does it cost to fill a pool?
At the US average of $4 to $6 per 1,000 gallons, a 15,000-gallon pool costs $60 to $90 in water. A 20,000-gallon pool is $80 to $120. Call your water utility before you start and ask about a sewer charge waiver for pool water.
Is it cheaper to fill with a garden hose or a water truck?
Garden hose tap water is significantly cheaper per gallon. A water truck costs $175 to $380 per load. The tradeoff is time. Two days of hose monitoring vs a few hours of waiting for the truck.
How long after filling can you swim?
Not right away. You need to balance the water chemistry first – pH, alkalinity, shock treatment. Plan on 24 to 48 hours after the pool is full before swimming. Fresh unbalanced tap water can irritate skin and eyes.
Does well water take longer to fill a pool?
The flow rate is similar to a garden hose, but you may need to fill in stages to let the well recover. The bigger issue is water quality – well water often contains metals that stain the pool instantly when chlorine is added. Test it before you start.