If you’ve ever tried to shock your pool and ended up wondering, “Wait, how much water is in here anyway?” — you’re not alone. Whether you’re opening for the season, adding pool chlorine tablets, or just trying to budget for your water bill, knowing your pool’s volume (in gallons) is the first step to getting it right.
Good news: it’s easier than it sounds. Let’s break it down by pool shape so you can get an accurate number with this handy calculator.
If your pool is one consistent depth all the way through, that’s your number. But if it has both a shallow and deep end, here’s a quick formula:
(Shallow End + Deep End) ÷ 2 = Average Depth
So if your shallow end is 3 feet and your deep end is 7.5 feet:
(3 + 7.5) ÷ 2 = 5.25 ft average depth
Important: Always use the actual water depth — not the pool wall height. Some above-ground pools list wall height in inches (like 48" or 52"), but the waterline is usually a few inches lower. Convert inches to feet by dividing by 12 (for example, 48" = 4 ft).
All pool volume calculations use this basic method:
Length × Width × Average Depth × a shape-specific multiplier
Rectangular or Square Pools
Formula:
Length × Width × Average Depth × 7.5
Example:
16 ft × 32 ft pool with 3 ft shallow and 7.5 ft deep ends
Average depth = 5.25 ft
16 × 32 × 5.25 × 7.5 = 20,160 gallons
Round Pools
Formula:
Diameter × Diameter × Average Depth × 5.9
Example:
24 ft round pool with a flat 4 ft bottom
24 ft × 24 ft × 4 ft × 5.9 = 13,593.6 gallons
Oval Pools
Formula:
Length × Width × Average Depth × 6.7
Use the longest and widest points of your oval pool.
Example:
12 ft × 24 ft pool with a 4.33 ft depth (converted from 52")
12 × 24 × 4.33 × 6.7 = 8,355.17 gallons
Kidney-Shaped Pools
Formula:
Average Width × Full Length × Average Depth × 7.0 - Average Width is determined by adding the widest points of your pool at each end and then dividing by 2.
(Widest point A + Widest point B) ÷ 2
Example:
32 ft long pool, widths of 14 ft and 17 ft, 3 ft shallow and 6 ft deep ends
Average width = 15.5 ft
Average depth = 4.5 ft
32 × 15.5 × 4.5 × 7 = 15,624 gallons
If your pool has unusual dimensions or sharp drop-offs, just split it into sections. Measure and calculate each section separately, then add the volumes together to get your total.
Now that you know your pool's size in gallons, it’s easier to:
Buy the correct size chemical kits
Add the right amount of pool shock
Use algaecide and stabilizer more effectively
Avoid wasting money or underdosing your pool
This is exactly where something like the Rx Clear® Spring Opening Pool Chemical Kit really comes in handy. It's available in three different sizes to match your pool’s gallon range, so you can get your water balanced quickly — no second guessing.
Don’t use the wall height to estimate volume.
Use the actual water level — not the height of the pool wall.
Don’t round too early.
A few inches can shift your gallon count by hundreds. Convert inches to feet (1 inch = 0.0833 feet).
Don’t assume “close enough” is good enough.
For pool opening and chemical dosing, accuracy prevents cloudy water, algae, or wasted product.
Do test your water after adding chemicals.
Use Rx Clear® 7-in-1 Pool & Spa Test Strips to check chlorine, pH, alkalinity, and more — fast and easy.
Once you’ve calculated your pool’s volume, you’re ready for the next step — getting your water clean, clear, and swim-ready.
The Rx Clear® Spring Opening Pool Chemical Kit comes in three sizes:
Kit A – for pools up to 7,500 gallons
Kit B – for pools up to 15,000 gallons
Kit C – for pools up to 30,000 gallons
Each kit includes chlorine shock, algaecide, stabilizer & conditioner, test strips, and easy-to-follow instructions.
Click here to choose your kit and take the guesswork out of opening your pool this year.
How do I know if I measured my pool correctly?
Measure from the waterline — not the top of the wall. If your pool has variable depths, calculate the average and use the appropriate shape formula.
Does the exact gallon count really matter for pool chemicals?
Yes — especially for shock and stabilizer. Too much can waste product or irritate skin. Too little, and your water stays cloudy or unbalanced.
What if my pool isn’t a perfect shape?
Split it into smaller sections and calculate them separately using the closest shape (rectangle, circle, etc.). Add the volumes together.
How many gallons are in a 24 ft round pool?
If it’s 4 ft deep:
24 × 24 × 4 × 5.9 = 13,593.6 gallons
Where can I get chemicals that match my pool size?
We recommend the Rx Clear® Spring Opening Pool Chemical Kit, available in sizes for pools up to 7,500, 15,000, and 30,000 gallons.
