How to Calculate Swimming Pool Volume in Gallons or Liters

Calculating swimming pool volume is essential for determining chemical requirements, filtration capacity, and water costs. Pool volume depends on shape, depth, and dimensions. Understanding how to calculate pool volume for different shapes ensures proper maintenance and operation of your swimming pool.

Rectangular Pool Volume

Formula:

Volume = Length × Width × Average Depth
Volume in gallons = Volume in cubic feet × 7.48

Example: Standard rectangular pool

Length: 20 feet
Width: 15 feet
Depth: 5 feet (assuming uniform)
Volume: 20 × 15 × 5 = 1,500 cubic feet
Gallons: 1,500 × 7.48 = 11,220 gallons

Non-Uniform Depth

For sloped pool bottoms:

Average Depth = (Deep end + Shallow end) ÷ 2
Volume = Length × Width × Average Depth

Example: Pool with slope

Length: 30 feet
Width: 20 feet
Shallow end: 3 feet
Deep end: 8 feet
Average depth: (3 + 8) ÷ 2 = 5.5 feet
Volume: 30 × 20 × 5.5 = 3,300 cubic feet
Gallons: 3,300 × 7.48 = 24,684 gallons

Circular/Round Pool Volume

Formula:

Volume = π × radius² × depth

Example: Round pool

Diameter: 18 feet
Radius: 9 feet
Depth: 4 feet
Volume: 3.14159 × 9² × 4 = 1,017.9 cubic feet
Gallons: 1,017.9 × 7.48 = 7,614 gallons

Kidney-Shaped or Irregular Pools

Divide into manageable sections:

Example approach:

Approximate as 2 rectangles + 1 semi-circle
Calculate each separately
Sum for total

Common Pool Sizes and Volumes

Water Chemical Calculations

Pool volume determines chemical dosages:

Example: Chlorine addition

Pool volume: 15,000 gallons
Chlorine needed: 1-3 ppm
Requires proper calculation based on testing

Water Circulation and Filtration

Pool pump sizing depends on volume:

Turnover rate: Water should circulate 1-2× daily
Pump capacity: Volume ÷ Turnover hours

Example: 20,000 gallon pool, 2× daily turnover

Daily circulation: 20,000 × 2 = 40,000 gallons
Pump needed: 40,000 ÷ 24 hours = 1,667 gallons/hour
Or: ~25 GPM pump

Fill Time Calculation

Calculate time to fill pool:

Fill time (hours) = Volume (gallons) ÷ Flow rate (gallons/hour)

Example:

Pool volume: 15,000 gallons
Hose flow rate: 60 gallons/minute = 3,600 gallons/hour
Fill time: 15,000 ÷ 3,600 = 4.17 hours (about 4 hours 10 minutes)

Water Cost Calculation

Estimate ongoing water costs:

Monthly cost = Volume × Water rate

Example:

Initial fill: 20,000 gallons
Water rate: $5 per 1,000 gallons
Evaporation/use: 500 gallons/week × 4 = 2,000 gallons/month
Monthly water cost: 2,000 × ($5/1,000) = $10

Chemical Cost by Pool Size

Volume Change with Season

Account for water loss:

Evaporation: 1/4 inch per day (0.5-1% of volume monthly)
Backwashing: 25-50% pool volume weekly
Maintenance: Drain and refill annually

Example: 20,000 gallon pool

Monthly evaporation: 20,000 × 0.5% = 100 gallons
Weekly backwash: 20,000 × 30% = 6,000 gallons/week = 1,500 gallons/month
Water loss: 100 + 1,500 = 1,600 gallons/month
Annual water cost: 1,600 × 12 × $0.005 = $96

Oval Pool Volume

Formula:

Volume = π × (Length/2) × (Width/2) × Depth

Example: Oval pool

Length: 30 feet
Width: 20 feet
Depth: 4 feet
Volume: 3.14159 × 15 × 10 × 4 = 1,885 cubic feet
Gallons: 1,885 × 7.48 = 14,099 gallons

Real-World Example: Backyard Pool

Dimensions: 15 × 30 feet
Shallow end: 3 feet
Deep end: 7 feet
Average depth: 5 feet

Volume: 15 × 30 × 5 = 2,250 cubic feet
Gallons: 2,250 × 7.48 = 16,830 gallons

Initial fill:
Water rate: $5 per 1,000 gallons
Cost to fill: 16,830 ÷ 1,000 × $5 = $84.15

Weekly water loss: ~125 gallons (evaporation)
Pump turnover: 16,830 ÷ 8 hours = 2,104 GPH needed

Chemical costs (monthly):
Chlorine: $20
Stabilizer: $8
Algaecide: $5
Test strips: $3
Total: ~$36/month

Pool Efficiency Tips

Reduce volume and costs:

• Reduce depth in shallow areas
• Use saltwater system (lower chemical cost)
• Proper cover reduces evaporation 95%
• Efficient pump lowers energy costs
• Proper circulation reduces chemical needs

Use our Pool Volume Calculator to instantly calculate pool volume for maintenance and cost planning.