Quick Answer
The volume of a swimming pool can be calculated by measuring the length, width, and depth of the pool and using the following formula:
Gallons = Length x Width x Average Depth x 7.5
Where:
– Length and Width are measured in feet
– Average Depth is measured in feet
– 7.5 is a conversion factor that converts cubic feet to gallons
So for example, if your pool is 20 feet long, 10 feet wide, and has an average depth of 5 feet, the calculation would be:
Gallons = 20 x 10 x 5 x 7.5 = 7,500 gallons
The average depth is important to factor in, since most pools have a sloped bottom and are deeper at one end. The average depth takes that into account.
Determining the Dimensions of Your Pool
The first step in calculating the volume of your pool is to determine the length, width, and average depth. Here are some tips for measuring each dimension:
Length – The length is the maximum distance from one end of the pool to the other. For irregularly shaped pools, you may need to break the pool into rectangles and triangles to calculate the total length.
Width – The width is the maximum distance side-to-side at the widest point. Again, break oddly shaped pools into geometric shapes.
Average Depth – For the average depth, you’ll need to take multiple depth measurements along the length of the pool. Measure the shallow end, deep end, and a few points in between. Then average those depths.
If you don’t have access to the actual pool to take measurements, check the original plans for the pool dimensions or contact the pool installer. Pool volume information may also be available from your local building permit office if an inspection was done during installation.
Using the Pool Volume Formula
Once you have accurate length, width, and average depth measurements, plug those numbers into the pool volume formula:
Gallons = Length x Width x Average Depth x 7.5
Let’s look at a few examples:
Pool 1 dimensions:
Length: 20 ft
Width: 10 ft
Average depth: 5 ft
Gallons = 20 x 10 x 5 x 7.5 = 7,500 gallons
Pool 2 dimensions:
Length: 15 ft
Width: 8 ft
Average depth: 6 ft
Gallons = 15 x 8 x 6 x 7.5 = 5,400 gallons
Pool 3 dimensions:
Length: 12 ft
Width: 16 ft
Average depth: 4 ft
Gallons = 12 x 16 x 4 x 7.5 = 5,760 gallons
As you can see, the pool volume formula is straightforward and easy to use once you have the right measurements.
Estimating Pool Volume
If you are unable to measure the dimensions of your existing pool, you can estimate the volume based on the pool shape and standard sizes. Here are some common pool shapes and average dimensions:
Kidney-shaped pool – 15 x 30 feet, 3 to 5 foot depth. Volume range: 2,800 – 9,000 gallons
Rectangular pool – 15 x 30 feet, 3 to 5 foot depth. Volume range: 3,300 – 11,250 gallons
Freeform pool – 15 x 30 feet, 3 to 5 foot depth. Volume range: 3,300 – 11,250 gallons
Round pool – 15 to 20 foot diameter, 3 to 5 foot depth. Volume range: 5,300 – 15,450 gallons
Oval pool – 15 x 30 feet, 3 to 5 foot depth. Volume range: 3,300 – 11,250 gallons
Again, these are just estimates based on typical pool sizes. The actual volume of your pool may vary. To get a more accurate estimate, take some measurements of the length/width and use Google Earth or satellite imagery to identify the pool shape and approximate dimensions. Combine that with an educated guess of the average depth and plug into the formula.
Factors that Affect Pool Volume
When estimating pool volume, keep in mind that several factors can alter the calculations:
– Shape irregularities – Freeform pools and other unique shapes make measurements difficult. Break the pool into geometric shapes for the formula.
– Slopes – Gradual slopes and pool floors that aren’t perfectly flat will affect the average depth used in the formula.
– Steps, benches, swim-outs – Built-in pool elements like these effectively decrease the volume. Factor them in when estimating depth.
– Raised walls or copings – Raised elements along the top rail can decrease the effective length/width. Account for them in measurements.
– High water level – The water level of the pool also impacts the calculations. If the pool is filled above the tile line, the effective depth is increased.
– Additions or renovations – Any pool additions, removed areas, or renovations will change the original dimensions and volume.
The more precise the measurements you can take, the closer your volume estimate will be. When in doubt, reduce length, width, and depth estimates slightly to ensure your pool volume calculation is conservative.
Volume Calculators for Pool Professionals
For pool builders and service professionals who need to regularly calculate pool volumes, there are a few handy pool calculators available online:
– Swimming Pool Volume Calculator from Arctic Spas – Includes formulas for rectangular, circular, and oval pools: https://arcticspas.com/hot-tub-and-pool-tools/swimming-pool-volume-calculator
– Calculators from Poolsupplyworld.com – Free calculators for rectangle/circle pools, pool water volume, liner size, and more: https://www.poolsupplyworld.com/pool-calculators
– Pool Calculator from Premier Pools & Spas – Calculates volumes for polygonal, rectangular, and oval pools: https://www.premierpoolsandspas.com/resources/pool-volume-calculator
These calculators allow you to plug in dimensions and quickly calculate the estimated volume in gallons. No math required! They are great simplified tools for pool builders and technicians to use out in the field.
Why Determine Pool Volume Accurately?
There are a few key reasons it is useful to know your pool’s volume in gallons:
– Determine how much water is needed to fill the pool. This is especially helpful when filling a new pool or refilling an existing pool after repairs.
– Properly size pool equipment like pumps, filters, and heaters which are rated for specific pool volumes.
– Estimate the amount of chemicals needed to maintain proper water chemistry and sanitization.
– Calculate the turnover rate or how long it takes for all water in the pool to run through the filtration system. Turnover time depends on flow rate and volume.
– Budget for ongoing maintenance costs which depend partly on the amount of water that needs to be treated. Larger pools have higher chemical, energy, and upkeep costs.
– Evaluate which size automatic pool cleaner to purchase based on the pool size/volume.
– Determine how much water needs to be drained when closing an in-ground pool for the winter.
– Estimate the amount of splash-out water loss over the course of a swimming season.
Accurately measuring and tracking your pool’s volume makes maintenance, repairs, upgrades, and seasonal closing much easier. It takes the guesswork out of key processes and purchasing decisions.
Using Pool Volume for Chemical Calculation
Knowing your pool’s volume is also extremely helpful when adding pool chemicals or adjusting water chemistry. Most chemical containers provide application rates in gallons treated per pound or fluid ounce.
Here are some examples for a 15,000 gallon pool:
– Liquid chlorine is added at a rate of 1 quart per 10,000 gallons. For a 15,000 gallon pool, that’s 1.5 quarts of liquid chlorine required.
– Granular chlorine is added at 10 oz per 10,000 gallons. For a 15,000 gallon pool, that’s 15 oz or just under 1 lb of granular chlorine required.
– Muriatic acid is added at a rate of 1.5 pints per 10,000 gallons to lower pH. For a 15,000 gallon pool, that comes out to 2.25 pints of acid required.
– Baking soda is added at 6 oz per 10,000 gallons to increase alkalinity. For our example pool, that would be 9 oz or just over half a pound.
As you can see, most chemical dosing relies on volume, so an accurate pool size makes maintaining proper chemistry much simpler.
Using Pool Volume for Heater Sizing
Sizing an appropriately powerful pool heater also depends on knowing the volume of water that needs to be heated. As a rule of thumb, you need about 100,000 BTUs of heating power for every 20,000 gallons of pool water.
So for our 15,000 gallon pool example, a pool heater between 75,000 to 100,000 BTUs would be appropriately sized to heat the water efficiently.
Undersizing the heater for your pool volume means the water will take much longer to reach desired temperatures. Oversizing is also a problem, since the heater may cycle on and off too frequently, leading to problems down the road.
Consult manufacturer sizing charts to choose the ideal heater based on your calculated pool volume. Proper sizing leads to efficient operation and years of trouble-free heating.
Using Pool Volume for Filtration
Swimming pool filtration systems should turn over the total water volume at least once every 12 hours. For our 15,000 gallon pool example:
15,000 gallons / 24 hours = 625 gallons per hour minimum filtration rate
This means you need a pump and filter sized to continuously filter at least 625 gallons per hour. If the flow rate is slower than this, increase the filtration time to achieve one full turnover every 24 hours.
Two turnovers per day (every 12 hours) is recommended for optimal water quality. Again, knowing your pool’s volume is key to proper pump and filter sizing for filtration.
How to Increase Pool Volume
Sometimes after measuring out your pool you determine the current volume is too small for your needs. Here are a few ways to increases the water volume if an existing pool comes up short:
– Resurface the interior with a new plaster finish. Over time plaster can erode, gradually decreasing pool depth. New plaster will restore the original depth.
– Convert to a saltwater chlorination system. The salt chlorine generator and cells take up space, so removing them gains a few inches of depth.
– Upgrade to small profile pool lights and remove bulky in-wall lighting niches to gain depth.
– Remove or reduce hybrid beach entries which take up shallow space.
– Eliminate bench seating or swimouts in small pools to increase overall depth.
– Resize the main drain suction covers to be as small as possible while meeting safety codes. This can add an inch or two of depth.
While remodeling options like these can help, the most impactful way to increase pool volume is to excavate and expand the size. But take care not to exceed property setback limits and backyard space.
Adding a spa or raised hot tub nearby is another way to increase the total backyard water volume without digging up the existing pool.
Estimating Volume When Building a Pool
If you’re planning a new pool installation, take advantage of the ability to customize the shape and dimensions to meet your needs. Here are some tips to design a pool with ideal volume:
– Allow for 1,500 to 2,000 gallons per swimmer. For a family of four, plan for 8,000 gallon minimum volume.
– Draw the shape and layout you want, then plug dimensions into a pool volume calculator. Tweak as needed.
– Remember that small changes in each dimension exponentially increase volume, so even a few feet make a difference.
– Compare multiple pool shape options – rectangle, kidney bean, free form, oval, etc. One may have more volume.
– Think vertical too – adding a foot of depth adds a lot of water versus just increasing length/width.
– Maximize depth for diving boards, slides, and use, while minimizing shallow areas.
– Determine how many gallons you realistically need vs. what backyard space allows. Work within constraints.
– Excavate the hole 2-3 inches deeper and gain depth with a sloped bottom floor.
By designing and excavating strategically, you can ensure your new pool has more than adequate volume for your needs and lifestyle from day one.
Pools With the Greatest Volume
For those looking to maximize swimming space and volume at all costs, here are some of the largest home pools in terms of sheer volume:
– The Largest Residential Pool in America (Cabo San Lucas, Mexico) – 4,800 square feet, 225,000 gallons
– Long Island Mega-Mansion Pool (Sagaponack, NY) – 70 feet long, 35 feet wide, depth over 8 feet, 750,000 gallons
– Fleckenstein Pool (Austin, TX) – 75 feet long, 40 feet wide, depth over 10 feet, 695,000 gallons
– Pensacola Beach Mansion Pool (Florida) – Supposedly holds 2 million gallons though dimensions unconfirmed
– Shoreline Mansion Indoor Pool (Washington) – 60 feet long, 40 feet wide, 500,000+ gallon capacity
For reference, even massive public Olympic-size pools only hold up to 660,000 gallons.
Truly enormous residential pools are rare, expensive to build and maintain, and require much more equipment and chemicals. But for the ultra-wealthy looking to make a statement, massive pools with the greatest volume imaginable are possible.
Conclusion
Determining your pool’s volume in gallons is hugely beneficial for maintenance tasks, choosing equipment, and performing water chemistry. While it takes a few simple measurements and calculations, the volume estimate will serve you well for the entire lifespan of the pool.
For oddly shaped pools, break the area into smaller rectangles and triangles to get length/width numbers for the formula. Or opt for an online pool volume calculator designed for unique shapes.
When planning a new pool, factor in desired usage and backyard space constraints. But also allow for adequate volume – around 2,000 gallons per regular swimmer is a good guideline. Design smartly and maximize depth where possible.
Getting the pool volume right from the start prevents headaches and ensures your pool meets the needs of homeowners for years to come.
