How Long Does It Take To Fill A Swimming Pool? (With Calculator)


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Water being added to an underground swimming pool.

Filling a swimming pool for the first time or after a drain will take quite some time.  If you have a small pool of 5,000 gallons or less you will easily be able to fill it in one day.  For others that are filling a much larger pool it could take multiple days until your pool water has reached capacity.

Assuming your water pressure is pumping at 8 gallons per minute (480 gallons per hour) through your outside water hose, it would take 31.25 hours to fill a 15,000 gallon swimming pool.

WATER PRESSURE

Water pressure is the biggest factor that can make a pool fill much slower or faster.  Your swimming pool can only add water as fast as your faucet will allow.

The average home outside faucet will usually pour somewhere between 4 to 12 gallons per  minute out of the water hose.

To determine exactly how long it is going to take to fill your swimming pool, you must first know a few things about your water pressure and swimming pool.

  •  Find out how many gallons per hours (GPH) that your faucet produces.
  • Determine how many gallon of water you swimming pool will hold to reach capacity.

Once you know these numbers it will be easy to determine a very accurate estimate to the length of time it will take from start to finish when filling your swimming pool.

How To Determine My GPH?

5 gallon bucket water

If you are unsure how many gallons per hour your water pressure pumps through you hose you can find this out quite easily.

There are a couple easy methods you can do with items you probably already have in your garage or backyard.

Active Time 3 minutes
Prep Time 5 minutes
Total Time 8 minutes
Difficulty Easy

Materials

  • Gallon Jug
  • Five Gallon Bucket
  • Water Hose

Tools

  • Calculator
  • Stop Watch

Instructions

Method 1 - Use Gallon Jug

  1. Have a friend hold a stop watch. This can be a simple timer app on a smartphone, or ask your Google Home or Alexa to time it if you have one.
  2. Using the same hose that you will be using to fill your swimming pool, place in position to fill a 1 gallon jug.
  3. Have your helper start the stop watch at the same time you begin adding water into the gallon jug.
  4. Press stop on the stop watch as soon as the jug is full.

Now you can easily calculate your GPH (Gallons Per Hour) by using the data you just gathered.

The formula we will be using to determine this is:
(60 ÷ Y) X 60 = GPH.
Y =
The number of seconds it took to fill the gallon jug.

Example: Assuming it took 10 seconds for completely fill 1 gallon of water the formula would be:
(60 ÷ 10) X 60 = 360 GPH.

To determine your GPM (Gallons Per Minute) divide the GPH by 60. In this example 360 ÷ 60 = 6 GPM.

Method 2 - 5 Gallon Bucket

  1. Grab a stop watch for someone else to operate on your command.
  2. Place the hose you will be using in your bucket.
  3. Tell the person with the stop watch to press start at the same time you turn on the water faucet.
  4. Yell "Stop the clock' as soon as the bucket is full.

While the gallon jug method is a very easy way of determining your water pressure, a bigger bucket can be slightly more accurate. Now you can calculate it.

In order to determine the GPM, use this formula:
(Bucket Size Gallons ÷ Seconds) X 60 = GPM.

Example: After doing steps 1 thru 4 you realize it takes 50 seconds to fill a 5 gallon bucket with your water house. Fill in the formula above:
(5 ÷ 50) X 60 = 6 GPM. To determine the GPH simply multiply the GPM by 60.

GPH = (GPM X 60)
GPH = (6 X 60) = 360 GPH.

Notes

You can use the 5 Gallon bucket formula with any size of bucket, simply plug in the numbers accordingly. You could even use it with 1 gallon jug method by replacing the gallon bucket size to 1 and the seconds to 10, you will find the results are the same.

HOW TO DETERMINE GALLONS OF WATER IN YOUR POOL.

If you know the dimensions of your swimming pool and the average water depth once filled there is a very simple formula you can use to determine water volume capacity.

The formula to determine your water capacity is different depending on the style of swimming pool you own. They will be classified below in 2 categories. Circular or Rectangle.

Circular pools will include any swimming pool that is in a round shape including oval pools as well.

Rectangle pools formula will apply to any square or rectangle pool. These will mostly be underground swimming pools, but there are some above ground pools in this style as well.

DETERMINE SWIMMING POOL WATER CAPACITY.

CIRCULAR WATER VOLUME FORMULA

Length in feet x length in feet x average depth in feet x 5.9 = Water capacity.

Lets try a couple examples below in determining the water capacity.

Example 1:  You have a 24 foot circular round swimming pool that is 52 inches deep.  The distance is going to be 24 feet across in all directions.  To determine the volume of water you would simply need to follow the formula.

24  length x 24 length x 4.5 feet depth x 5.9 = 15,292 gallon of water.

Example 2:  You own an oval pool that is 30 feet long at the longest point.  It is also 20 feet across on average from the shortest distance and is 48 inches deep.

30 length x 20 length x 4 feet depth x 5.9 = 14,160 gallons of water.

The formula is quite simple.  Simply L x L x D x 5.9.  This will give you the water volume needed to fill your aquatics and / or swimming pool.

RECTANGLE WATER VOLUME FORMULA

Length in feet x length in feet x average depth in feet x 7.5Water capacity.

I will give a an example for this type of swimming pool in determining water capacity.

Example: Your pool is 30 feet long x 10 feet wide and is 7 feet deep in the deep end. It is 4 feet deep in the shallow end.

30 length x 10 length x 5 feet deep average x 7.5 = 11,250 Gallons. In determining the average water depth I simply average a close middle ground number between the highest and lowest point of the pool. If your pool is more deep and shallow or vice versa you will need to make adjustments accordingly. You may not get exact figures, but will definitely be in the ball park.

Pool Fill Estimates Chart

Below is a chart that should also help you in determining about how long you can expect it to take for your swimming pool based on the shown water pressure of Gallons Per Minute.

Capacity
Gallons
Hours
7 GPM
Hours
8 GPM
Hours
9 GPM
Hours
10 GPM
< 1,000< 2 1/2< 2< 2< 2
5,0001210 3/49 1/48 1/3
10,00023 3/420 3/418 1/216 2/3
15,00035 3/431 1/427 3/425
20,00047 2/341 2/33733 1/3
25,00059 1/25246 1/441 2/3

START FILLING YOUR POOL WITH WATER

Now that you have determined your water volume and your water hose GPH you can determine how long it will take to fill your pool and start filling right away,

It is recommended you know precisely how long it will take when you begin the filling process of your swimming pool so you can easily determine how many hours remain before the water reaches maximum levels.

This will allow you to sleep with ease during nap time or overnight without worrying if you swimming pool has a chance of overflowing.

When leaving the hose unattended be sure it is attached in a way that it will not slither out of the pool.  This could cost hundreds of wasted gallons of water that does nothing but soak your lawn and can occur once the water begins to rise.As the water begins to fill, it is best to try and remove wrinkles and bends in the liner prior to the water covering the entire bottom.

Once the bottom is covered with water the weight of the water will take over and it will be hard to remove wrinkles.  At this time the bottom will be shown as it is now for the remainder of the water fill and your swimming season.

If there are other family members using water at the same time your swimming pool is being filled, it may slow down the filling process.

I would recommend avoiding watering the yard or other major use of water during this time.  It will cause your water pressure to decrease making your GPH drop and causing a longer fill time.

Small appliances such as the dishwasher and washing machine will not be enough to affect the pool filling process long term and can be continued as normal without much affect on the total time.

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