How to use the pool volume calculator
- Select your pool shape from the dropdown menu.
- Enter the required dimensions in feet. For sloped floors, provide both the shallow and deep depths.
- Read the results instantly: the tool shows capacity in US gallons, liters and cubic feet.
- Use the output to size pumps, order chemicals or estimate fill costs.
Formulas used for each pool shape
The pool volume calculator applies the standard geometric formulas and common pool-industry rules of thumb. All measurements are in feet, and the result in cubic feet is multiplied by 7.48 to convert to US gallons.
Rectangular: Length x Width x Average Depth x 7.48
Round: π x Radius² x Average Depth x 7.48, where radius is half the diameter.
Oval: 0.785 x Length x Width x Average Depth x 7.48. The 0.785 factor is pi / 4, the exact ratio of an ellipse area to its bounding rectangle.
Kidney: 0.45 x (Width A + Width B) x Length x Average Depth x 7.48. The 0.45 factor is a pool-industry rule of thumb for the irregular outline of a typical kidney shape, so treat the result as an estimate.
Average depth is computed as (Shallow Depth + Deep Depth) / 2. If the floor is flat, enter the same number for both fields.
Worked example: rectangular pool
Suppose you have a rectangular pool that is 20 feet long, 10 feet wide, 3 feet deep at the shallow end and 6 feet deep at the deep end.
- Average depth = (3 + 6) / 2 = 4.5 feet.
- Cubic feet = 20 x 10 x 4.5 = 900 ft³.
- US gallons = 900 x 7.48 = 6,732 gallons.
- Liters = 6,732 x 3.78541 = 25,483.4 liters.
This matches what the pool gallon calculator displays when you enter those dimensions. You can verify the math with a general volume calculator if you prefer to work in cubic feet first.
Common pool sizes reference table
The table below lists approximate capacities for popular residential pool sizes assuming a constant depth of 4 feet. Use these as quick benchmarks before entering exact measurements.
| Shape | Dimensions (ft) | Approx. gallons |
|---|---|---|
| Rectangular | 12 x 24 | 8,617 |
| Rectangular | 16 x 32 | 15,319 |
| Round | 15 dia. | 5,293 |
| Round | 24 dia. | 13,550 |
| Oval | 15 x 30 | 10,575 |
| Kidney | 20 L, 10+6 W | 4,308 |
For round shapes like hot tubs, the formula is identical to a circular pool. A dedicated cylinder volume calculator uses the same underlying math.
Practical uses for knowing your pool capacity
Accurate water volume is essential for several maintenance tasks:
- Chemical dosing: Chlorine, pH adjusters and algaecides are dosed per 10,000 gallons. Overestimating leads to harsh water; underestimating leaves it unsanitized.
- Pump and filter sizing: Turnover rate depends on total gallons. Most codes require filtering the entire volume every 6 to 8 hours.
- Heater selection: BTU requirements scale directly with water volume.
- Pool liner replacement: When ordering a new liner, installers need the exact dimensions and volume to ensure a proper fit. Using this tool as a pool liner calculator step helps avoid costly mistakes.
- Fill cost estimation: Municipal water rates are billed per 1,000 gallons or per cubic foot. Knowing the total lets you budget for filling or topping off.
Hot tubs and small spas
This tool also works as a hot tub volume calculator. Select the round shape and enter the interior diameter and water depth. Most residential hot tubs hold between 250 and 500 gallons. Because hot tubs use higher concentrations of sanitizers, precision matters even more than with large pools. Measure the water depth from the floor to the fill line, not the total shell height, to get an accurate reading.
Common mistakes to avoid
Several errors lead to incorrect pool volume estimates:
- Mixing units: Always measure in feet. If you measured in inches, divide by 12 first. Entering inches directly inflates the result by a factor of 1,728.
- Ignoring slope: A pool with a 3-foot shallow end and a 6-foot deep end does not average 6 feet. Use the average depth formula.
- Using diameter instead of radius: The round pool formula requires the radius. This tool accepts diameter and halves it internally, but if you do manual math, remember to divide.
- Measuring the outside of the wall: For above-ground pools, measure the inside diameter. Wall thickness can subtract several inches, which changes the gallon count noticeably on smaller pools.
Worked examples
| Example | Input | Result |
|---|---|---|
| Standard rectangular pool | Pool shape: rectangular; Length (ft): 20; Width (ft): 10; Shallow depth (ft): 3; Deep depth (ft): 6 | Volume (US gallons): 6,732; Volume (liters): 25,483.4; Volume (cubic feet): 900; Average depth (ft): 4.5; Surface area (sq ft): 200 |
| Round above-ground pool | Pool shape: round; Diameter (ft): 15; Shallow depth (ft): 4; Deep depth (ft): 4 | Volume (US gallons): 5,287.3; Volume (liters): 20,014.6; Volume (cubic feet): 706.86; Average depth (ft): 4; Surface area (sq ft): 176.71 |
| Oval pool | Pool shape: oval; Length (ft): 18; Width (ft): 12; Shallow depth (ft): 4; Deep depth (ft): 4 | Volume (US gallons): 5,075.81; Volume (liters): 19,214; Volume (cubic feet): 678.58; Average depth (ft): 4; Surface area (sq ft): 169.65 |
| Kidney-shaped pool | Pool shape: kidney; Length (ft): 25; Shallow depth (ft): 3; Deep depth (ft): 5; Width A (ft): 12; Width B (ft): 8 | Volume (US gallons): 6,732; Volume (liters): 25,483.4; Volume (cubic feet): 900; Average depth (ft): 4; Surface area (sq ft): 225 |
| Small hot tub | Pool shape: round; Diameter (ft): 7; Shallow depth (ft): 3; Deep depth (ft): 3 | Volume (US gallons): 863.59; Volume (liters): 3,269.1; Volume (cubic feet): 115.45; Average depth (ft): 3; Surface area (sq ft): 38.48 |
FAQ
How many gallons are in a 16x32 pool?
A 16x32 foot rectangular pool with an average depth of 4 feet holds about 15,319 US gallons. Enter your exact depths into the pool volume calculator for a precise figure.
What is the formula for a round pool?
Multiply pi by the radius squared, then by the average depth, then by 7.48. The radius is half the diameter.
Can I use this as a hot tub volume calculator?
Yes. Select the round shape, enter the interior diameter and the water depth from the floor to the fill line. The tool returns the capacity in gallons and liters.
Why does my chemical dosage seem wrong?
Chemical labels specify amounts per 10,000 gallons. If your pool gallon calculation is off, you will over-dose or under-dose. Re-measure your dimensions carefully and use the average depth, not the maximum depth.
Does this help me buy a pool liner?
Knowing the exact volume and dimensions is a key step when ordering a replacement liner. Installers use these numbers alongside the shape profile to cut the material correctly.
Is the conversion factor exactly 7.48?
One cubic foot equals approximately 7.48052 US gallons. Industry guides commonly round to 7.48, and this tool uses that standard factor to match the values printed on most pool chemical labels.
Do I need to account for steps or benches?
Built-in steps and benches displace water, so the actual capacity is slightly less than the geometric formula suggests. For most residential pools the difference is under 2 percent and can be ignored for chemical dosing.