Pool Volume Calculator — Round, Oval & Rectangular Pool Gallons

Q: Can I use this calculator for hot tubs?

Yes, but for hot tubs and spas, use our dedicated Hot Tub Calculator which accounts for spa-specific chemistry needs.

Q: What if my pool is an irregular shape?

For kidney-shaped or freeform pools, select Kidney / Irregular in the calculator. Measure the longest length and widest width. The calculator will estimate volume using these dimensions. For very complex shapes, you may need to divide the pool into sections and calculate each separately.

Calculate your pool size in gallons — required for all chemical calculations. Works for rectangular, oval, round, and kidney-shaped pools. No sign-ups. Instant results.

💡 Quick answer — pool volume formulas

Rectangular pool: Length × Width × Avg Depth × 7.5 = gallons
Round pool: Diameter × Diameter × Avg Depth × 5.9 = gallons
Oval pool: Length × Width × Avg Depth × 5.9 = gallons
Average depth: (Shallow depth + Deep depth) ÷ 2
18 ft round pool (4 ft deep) → 7,646 gal | 21 ft round pool (4 ft deep) → 10,408 gal
18×33 oval pool (4 ft deep) → 14,058 gal | 18×54 oval pool (4 ft deep) → 22,996 gal
Use the calculator below for all shapes and sloped bottoms.

Calculator

💡 Tip: Write down your pool volume — you'll need it for every other calculator.

Now that you know your pool volume — get your chemicals ready:

Example calculation

Let's calculate the volume of a typical rectangular pool:

Measurement	Value
Length	30 feet
Width	15 feet
Shallow end depth	3 feet
Deep end depth	8 feet
Average depth	5.5 feet (3 + 8) ÷ 2
Pool volume	18,562 gallons

Formula: 30 × 15 × 5.5 × 7.5 = 18,562 gallons

Pool volume formulas by shape

Rectangular pools

Formula: Length × Width × Average Depth × 7.5 = Gallons
Why 7.5? There are 7.5 gallons in one cubic foot of water.

Round pools — how many gallons by diameter

Formula: Diameter × Diameter × Average Depth × 5.9 = Gallons
Why 5.9? This accounts for the circular area (π × radius²) and converts to gallons.
Examples: 18 ft round pool (4 ft deep) = 7,646 gal | 21 ft round pool (4 ft deep) = 10,408 gal | 24 ft round pool (4 ft deep) = 13,594 gal

Oval pools — gallons for common sizes

Formula: Length × Width × Average Depth × 5.9 = Gallons
Similar to round pools but uses length and width instead of diameter.
Examples: 18×33 oval (4 ft deep) = 14,058 gal | 18×54 oval (4 ft deep) = 22,996 gal

Kidney or irregular shaped pools

For irregular shapes, measure the longest length and widest width, then multiply by 0.85 to account for the curved sections. Or divide the pool into sections (rectangular + round) and add them together.

How to measure your pool accurately

📏 Use a measuring tape

A 50-100 foot measuring tape works best. Walk the perimeter and measure straight lines for length and width.

💧 Measure water depth

Always measure to the actual water level, not the pool height. Use a pole or weighted string to measure depth.

📐 Calculate average depth

For sloped pools: (shallow depth + deep depth) ÷ 2. Example: (3ft + 8ft) ÷ 2 = 5.5ft average.

🔄 Measure multiple times

Measure twice to ensure accuracy. Being off by a foot can mean 1,000+ gallons difference in calculations.

💡 Use a reliable pool test kit to verify your pool volume calculation is accurate by testing how chemicals affect your water.

Why pool volume matters

Every pool chemical dosage is based on your pool's volume. Adding too little chlorine won't sanitize the water. Adding too much can irritate swimmers and damage equipment. An accurate volume calculation ensures you add the right amount every time.

Most pool owners estimate their volume and end up being off by 2,000-5,000 gallons. This leads to imbalanced chemistry, cloudy water, and wasted money on excess chemicals. Take 5 minutes to measure your pool properly — you only need to do it once.

Pool volume calculator FAQs

How do I calculate my pool volume in gallons?

Measure your pool's length, width, and depth. For rectangular pools, multiply length × width × average depth × 7.5. For round pools, multiply diameter × diameter × average depth × 5.9. Our calculator does the math automatically.

Why do I need to know my pool volume?

Pool volume determines how much of each chemical to add. Adding the wrong amount can make your pool unsafe to swim in or damage your equipment. Accurate volume measurements ensure proper chemical balance.

What if my pool has a sloped bottom?

Measure the shallow end depth and deep end depth. Add them together and divide by 2 to get average depth. For example, if the shallow end is 3 feet and deep end is 8 feet, the average depth is 5.5 feet.

Do I measure to the top of the pool or the water line?

Always measure to the actual water depth, not the height of the pool walls. Measure from the water surface down to the bottom at both the shallow and deep ends.

Can I use this calculator for hot tubs?

Yes, but for hot tubs and spas, we recommend using our dedicated Hot Tub Calculator which accounts for spa-specific chemistry needs.

How accurate does my pool volume need to be?

Try to be within 500 gallons for pools under 20,000 gallons, and within 1,000 gallons for larger pools. Small errors in measurement (1-2 feet) can result in significant volume differences.

What if my pool is an irregular shape?

For kidney-shaped or freeform pools, select "Kidney / Irregular" in the calculator. Measure the longest length and widest width. The calculator will estimate volume using these dimensions. For very complex shapes, you may need to divide the pool into sections and calculate each separately.