Calculate Volume of Kidney Shaped Pool: Practical Math, Formulas, and Chemical Guide

Kidney-shaped swimming pools are beloved by homeowners for their organic, soft curves that blend harmoniously into natural garden landscapes. Unlike traditional rectangular pools with crisp straight angles, a kidney pool mimics natural lagoons with an indentation on one side dividing the body of water into two distinct circular lobes (the shallow end and the deep end). However, this fluid geometry often leaves pool owners puzzled when it comes time to determine water capacity: how do you accurately calculate volume of kidney shaped pool without complex calculus?

Knowing your pool’s exact gallonage or cubic meter capacity is essential for proper chemical balancing, selecting the right variable-speed pump, and correctly sizing pool heaters or salt chlorine generators. Here is your definitive calculation guide.

1. Understanding the Geometry: The Two-Diameter Method

Contractors and hydraulic engineers approximate the surface area of a kidney pool by treating it as two connected circles of unequal size joined by a narrower waist.

To perform the calculation, you need five critical field measurements:

1. Length ($L$): The longest straight-line dimension running from one end of the pool to the other.
2. Width of Lobe A ($W_1$): The widest point across the shallow end.
3. Width of Lobe B ($W_2$): The widest point across the deep end.
4. Shallow End Depth ($D_1$): Water level height at the shallowest point.
5. Deep End Depth ($D_2$): Water level height at the deepest point.

2. The Standard Formulas for Kidney Pools

Step 1: Calculate Average Depth ($D_{avg}$)

$$D_{avg} = \frac{D_1 + D_2}{2}$$

Step 2: Calculate Volume in US Gallons (Imperial Units)

The pool industry applies an empirical geometric constant of 0.45 to compensate for the curved indentation:

$$\text{Volume (Gallons)} = (W_1 + W_2) \times L \times 0.45 \times D_{avg} \times 7.48$$ (since 1 cubic foot of water contains 7.48 US gallons).

Step 3: Calculate Volume in Metric Units (m³ or Liters)

If measuring in meters:

$$\text{Volume (m³)} = (W_1 + W_2) \times L \times D_{avg} \times 0.45$$

$$\text{Volume (Liters)} = \text{Volume (m³)} \times 1,000$$

3. Step-by-Step Practical Calculation Example

Let us calculate the water volume of a classic backyard kidney pool:

• Total Length ($L$): 30 feet
• Width Lobe A (Shallow end, $W_1$): 14 feet
• Width Lobe B (Deep end, $W_2$): 18 feet
• Shallow depth ($D_1$): 3.5 feet
• Deep depth ($D_2$): 6.5 feet

Step 1: Find average depth

$$D_{avg} = \frac{3.5 + 6.5}{2} = 5.0\text{ feet}$$

Step 2: Sum the lobe widths

$$W_1 + W_2 = 14 + 18 = 32\text{ feet}$$

Step 3: Compute the volume in gallons

$$\text{Volume} = 32\text{ ft} \times 30\text{ ft} \times 0.45 \times 5.0\text{ ft} \times 7.48 \approx 16,157\text{ US Gallons}$$

When you calculate volume of kidney shaped pool using this standard method, your pool holds approximately 16,200 gallons of water (approx. 61.3 m³).

4. Kidney Pool Volume Estimation Chart

This quick reference guide outlines typical volume ranges for standard pre-formed fiberglass and custom gunite kidney pools:

Dimensions ($L \times W_1 / W_2$)	Average Depth	Estimated Gallons (US)	Estimated Cubic Meters (m³)
20’ $\times$ 10’ / 12’	4.5 ft	7,400 – 8,000 gal	28 – 30 m³
26’ $\times$ 12’ / 15’	4.8 ft	11,500 – 12,500 gal	43 – 47 m³
30’ $\times$ 14’ / 18’	5.0 ft	15,500 – 16,500 gal	59 – 62 m³
34’ $\times$ 16’ / 20’	5.5 ft	21,500 – 23,000 gal	81 – 87 m³
40’ $\times$ 18’ / 24’	6.0 ft	32,000 – 34,500 gal	121 – 130 m³

5. Why Accurate Volume Matters for Kidney Pools

• Chemical Dosages: Adding algaecides, clarifiers, or stabilizer (cyanuric acid) requires precise dosing per 10,000 gallons. Guessing can lead to cloudy water or chemical burns.
• Pump Turnover Rate: Residential health standards recommend circulating the entire pool volume within 8 hours: $$\text{Minimum Flow Rate (GPM)} = \frac{\text{Pool Volume (Gallons)}}{8 \times 60 \text{ minutes}} = \frac{16,200}{480} \approx 33.75\text{ GPM}$$ Your filtration pump must sustain at least 34 gallons per minute.
• Saline Chlorination: If you run a salt system, reaching the target 3,200 ppm salt concentration requires adding precisely calculated 40-lb bags of pool salt upon initial startup.

Conclusion

Learning how to determine water capacity comes down to splitting the unique silhouette into two balanced circular lobes and applying the 0.45 geometric correction coefficient. Having this figure written in your equipment room takes the guesswork out of water maintenance and protects your investment season after season.

Want an instant calculation without the manual math? Try our online kidney shaped pool volume calculator to find your exact pool gallonage and liter capacity in seconds!