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Pool Volume Calculator

Calculate pool volume and chemical needs

Pool Volume

21,064 gal

Liters

79,726

Fill Time

39h

Units

Pool Volume

21,064

gallons

Liters

79,726

Cubic Feet

2,816

Water Cost

$105

Fill Time (garden hose)

~39 hours (1.6 days)

Chemical Requirements (Weekly)

Chlorine

16.9 oz

Liquid or tablets

Shock Treatment

2.1 lbs

Weekly shock

Algaecide

8.4 oz

Prevention dose

pH Balancer

3.2 lbs

As needed

Common Pool Sizes

Small (12x24 ft)~10,000 gallons
Medium (16x32 ft)~20,000 gallons
Large (20x40 ft)~30,000 gallons
Olympic (82x164 ft)~660,000 gallons

Volume Formulas

Rectangle:

Length × Width × Avg Depth × 7.48

Oval:

Length × Width × Avg Depth × 5.9

Round:

Diameter² × Avg Depth × 5.9

Kidney/Freeform:

Length × Width × Avg Depth × 6.4

Volume Comparison

Gallons21.1k
Liters79.7k
Cubic Feet2.8k

What You'll Need

Taylor K-2006C Complete Pool Water Test Kit

Taylor K-2006C Complete Pool Water Test Kit

$80-$1004.7
View on Amazon
HTH Super 3" Chlorinating Tablets 5lb

HTH Super 3" Chlorinating Tablets 5lb

$30-$404.5
View on Amazon
Taylor K-2006C Complete Pool Water Test Kit

Taylor K-2006C Complete Pool Water Test Kit

$80-$1004.7
View on Amazon
HTH Super 3" Chlorinating Tablets 5lb

HTH Super 3" Chlorinating Tablets 5lb

$30-$404.5
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Frequently Asked Questions

Q

How do I calculate my pool volume in gallons?

For rectangular pools: Length × Width × Average Depth × 7.48. For round pools: Diameter² × Depth × 5.9. For oval pools: Length × Width × Depth × 5.9. These formulas give you the volume in gallons.

  • Rectangular: 32 × 16 × 5.5 ft avg depth × 7.48 = 21,064 gallons
  • Round: 18² × 4 ft depth × 5.9 = 7,646 gallons
  • Average depth = (shallow end + deep end) / 2 for gradual-slope pools
  • For freeform or kidney shapes, multiply by 0.85 to account for curves
  • 1 cubic foot = 7.48052 gallons — this is the key conversion factor
Q

How many gallons is an average pool?

Average inground pools hold 15,000-30,000 gallons. A typical 16×32 ft pool with 5 ft average depth holds about 19,200 gallons. Above-ground pools typically hold 5,000-15,000 gallons.

  • Small above-ground (12 ft round, 4 ft deep): ~3,400 gallons
  • Large above-ground (24 ft round, 4.5 ft deep): ~15,300 gallons
  • Average inground (16 × 32 ft, 5 ft avg): ~19,200 gallons
  • Large inground (20 × 40 ft, 6 ft avg): ~35,900 gallons
  • Olympic pool (164 × 82 ft, 6.5 ft): ~660,000 gallons
Pool TypeTypical SizeApproximate Volume
Above-Ground (Small)12 ft round × 4 ft3,400 gallons
Above-Ground (Large)24 ft round × 4.5 ft15,300 gallons
Inground (Average)16 × 32 ft × 5 ft19,200 gallons
Inground (Large)20 × 40 ft × 6 ft35,900 gallons
Q

How long does it take to fill a pool?

With a standard garden hose (9 GPM), filling a 20,000-gallon pool takes about 37 hours or 1.5 days of continuous flow. Using multiple hoses or a fire hydrant fill service can reduce this significantly.

  • Standard garden hose: 9 GPM = 540 gal/hour = 12,960 gal/day
  • Two hoses: doubles flow to ~18 GPM, fills 20,000 gal in ~18.5 hours
  • Fire hydrant fill service: 500–1,500 GPM, fills a pool in 15–40 minutes ($200–$500)
  • Some water utilities offer a "pool fill" rate — call ahead to avoid sewer surcharges
  • Never leave a filling pool unattended overnight — use a timer shutoff valve
Q

Why is knowing pool volume important?

Pool volume determines proper chemical dosing. Too little chlorine won't sanitize; too much can irritate skin and damage equipment. Accurate volume ensures proper pH balance, algae prevention, and safe swimming conditions.

  • Chlorine dose: 2 oz of liquid chlorine per 10,000 gallons raises free chlorine by ~1 ppm
  • pH adjustment: 6 oz of muriatic acid per 10,000 gallons lowers pH by ~0.2
  • Shock treatment requires accurate volume — underdosing won’t kill algae effectively
  • Salt pools need 50 lbs of salt per 2,000 gallons to reach the ideal 3,200 ppm range
Q

How much does it cost to fill a pool with water?

At average US water rates ($0.004-$0.006 per gallon), filling a 20,000-gallon pool costs $80-$120. Some areas charge more. Municipal pools may qualify for reduced rates or use hydrant fill services.

  • US average water rate: $0.004–$0.006/gallon or $4–$6 per 1,000 gallons
  • Filling a 15,000-gallon pool: $60–$90; a 30,000-gallon pool: $120–$180
  • California and Northeast rates can reach $0.01/gallon, doubling the cost
  • Water truck delivery: $200–$600 for 6,000 gallons, faster but more expensive per gallon
  • Many utilities waive sewer charges for pool fills if you call them before filling

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Example Calculations

1Rectangular Pool (32 × 16 ft)

Inputs

ShapeRectangle
Length32 ft
Width16 ft
Shallow End3 ft
Deep End8 ft

Result

Pool Volume21,064 gallons
Liters79,727
Cubic Feet2,816
Fill Time~39 hours (1.6 days)
Water Cost$105

Average depth = (3 + 8) / 2 = 5.5 ft. Cubic feet = 32 × 16 × 5.5 = 2,816. Gallons = 2,816 × 7.48 = 21,064. Fill time at 9 GPM = 21,064 / 540 = 39 hours.

2Round Pool (18 ft diameter)

Inputs

ShapeRound
Diameter18 ft
Shallow End3 ft
Deep End5 ft

Result

Pool Volume7,614 gallons
Liters28,821
Cubic Feet1,018
Fill Time~14.1 hours (0.6 days)
Water Cost$38

Average depth = (3 + 5) / 2 = 4 ft. Radius = 18 / 2 = 9 ft. Cubic feet = π × 9² × 4 = 1,018. Gallons = 1,018 × 7.48 = 7,614. Fill time at 9 GPM = 7,614 / 540 = 14.1 hours.

Formulas Used

Rectangular Pool Volume

Gallons = Length × Width × Avg Depth × 7.48

Calculates volume for a rectangular pool by multiplying dimensions in feet to get cubic feet, then converting to gallons.

Where:

Length= Pool length in feet
Width= Pool width in feet
Avg Depth= (Shallow End + Deep End) / 2 in feet
7.48= Gallons per cubic foot conversion factor

Round Pool Volume

Gallons = π × (Diameter / 2)² × Avg Depth × 7.48

Calculates volume for a circular pool using the area of a circle times depth, converted to gallons.

Where:

Diameter= Pool diameter in feet
Avg Depth= (Shallow End + Deep End) / 2 in feet
π= 3.14159

Fill Time Estimate

Fill Hours = Gallons / (9 × 60)

Estimates fill time using a standard garden hose flow rate of 9 gallons per minute.

Where:

Gallons= Pool volume in gallons
9= Garden hose flow rate in GPM

Understanding Pool Volume Calculations

1

Volume Formulas by Pool Shape

A standard 16×32 ft rectangular pool at 5.5 ft average depth holds approximately 21,064 gallons — nearly 80,000 liters of water that needs precise chemical treatment. The formula is straightforward: Length × Width × Average Depth × 7.48 (the gallons-per-cubic-foot conversion factor). Round pools use π × radius² × depth × 7.48, while oval pools multiply 0.89 × Length × Width × depth × 7.48.

Kidney and freeform shapes lose roughly 15% of volume compared to a rectangle of the same bounding dimensions. The calculator applies a 0.85 multiplier for these shapes. If your pool has an irregular outline, measure the widest and longest points and use the freeform formula — the result will be within 5–10% of actual volume.

Average depth is the single largest source of error. For a gradual-slope pool, simply average the shallow and deep ends: (3 ft + 8 ft) / 2 = 5.5 ft. Pools with a sharp drop-off (wading shelf to deep end) should be split into two rectangles and calculated separately, then summed. Use the pond liner calculator for irregular water features that don’t fit standard pool shapes.

D = average depth. Round uses diameter for the length input.
Pool ShapeFormulaExample (ft)Volume (gal)
RectangleL × W × D × 7.4832×16×5.521,064
Roundπ × r² × D × 7.4818 dia × 47,614
Oval0.89 × L × W × D × 7.4830×15×514,984
Kidney0.85 × L × W × D × 7.4832×16×5.517,904
2

Chemical Dosing by Pool Volume

Chlorine dosing precision depends entirely on accurate volume: 0.13 oz of liquid chlorine (12.5% sodium hypochlorite) per 1,000 gallons raises free chlorine by 1 ppm. A 20,000-gallon pool therefore needs 2.6 oz to bump chlorine from 1 ppm to 2 ppm — the ideal range recommended by the CDC.

Overestimating volume by just 20% means overdosing by 20%, which can bleach vinyl liners and irritate swimmers’ eyes at concentrations above 5 ppm. Underestimating is equally dangerous: a pool at 0.5 ppm free chlorine fails to kill E. coli within the required 60-second contact time.

Salt chlorine generators need 50 lbs of pool-grade salt per 2,000 gallons to reach the target 3,200 ppm. A 20,000-gallon pool requires 500 lbs of salt for initial setup — roughly 10 bags at $6 each. Use the rain barrel calculator to estimate how much rainwater dilution your pool receives during storm season, which lowers salt concentration.

Doses assume standard concentrations. Always follow product label instructions.
ChemicalDose per 10,000 galTarget RangeCost/Treatment
Liquid Chlorine (12.5%)1.3 oz per 1 ppm1–3 ppm$0.50–$1.00
Muriatic Acid (pH down)6 oz per −0.2 pH7.2–7.8 pH$0.30–$0.60
Shock (cal-hypo)1 lb10+ ppm$3–$5
Algaecide3–6 ozN/A$1–$2

The CDC recommends 1–3 ppm free chlorine and pH 7.2–7.8 for residential pools. Test water at least twice weekly during swim season.

3

Fill Time and Water Cost Estimates

A standard garden hose delivers roughly 9 gallons per minute (540 gal/hr), so filling a 20,000-gallon pool takes approximately 37 hours — over 1.5 days of continuous flow. Running two hoses simultaneously cuts that to about 18.5 hours, while a fire hydrant fill service at 500–1,500 GPM finishes in 15–40 minutes for $200–$500.

At the US average water rate of $4–$6 per 1,000 gallons, filling a 20,000-gallon pool costs $80–$120. High-cost markets like San Diego ($14/1,000 gal) push fill cost to $280. Many utilities waive sewer charges for pool fills if you call ahead, saving an additional 30–50% since the water doesn’t enter the sewer system.

Evaporation removes 0.25–0.5 inches of water per week in summer, which translates to 90–180 gallons weekly for a 16×32 ft pool. That’s roughly $20–$50 per month in makeup water. A pool cover reduces evaporation by up to 95%, paying for itself within a single season. Use the rainwater harvesting calculator to see if collected rainwater can offset some evaporation losses.

Fill MethodFlow RateTime (20,000 gal)Cost
Single Garden Hose9 GPM37 hours$80–$120 (water only)
Two Hoses18 GPM18.5 hours$80–$120 (water only)
Water Truck (6,000 gal)Bulk4 trips$800–$2,400
Fire Hydrant Service500–1,500 GPM15–40 min$200–$500
4

Seasonal Maintenance by Pool Size

Annual chemical costs scale directly with volume: a 15,000-gallon pool averages $300–$500/year in chemicals, while a 30,000-gallon pool runs $600–$1,000. The largest variable is shock frequency — pools used heavily or exposed to rain need shocking every 1–2 weeks at $3–$5 per treatment per 10,000 gallons.

Pump runtime also depends on volume. The general rule is to turn over the entire pool volume once per 8–12 hours. A 20,000-gallon pool with a 50 GPM pump needs 6.7 hours of runtime daily. At $0.12/kWh and a 1.5 HP pump drawing 1.2 kW, that’s roughly $0.96/day or $29/month in electricity. Undersizing your pump for the pool volume means poor circulation and increased chemical demand.

Winter closing costs $150–$400 depending on pool size. The process requires draining water below the skimmer line (losing 3,000–5,000 gallons on a typical inground pool), adding winterizing chemicals proportional to volume, and covering. Knowing exact gallonage prevents both chemical waste and the risk of freeze damage from an improperly treated pool.

  • Test pH, chlorine, and alkalinity at least twice per week during swim season
  • Run the filter pump 8–12 hours daily to turn over the full pool volume
  • Shock the pool every 1–2 weeks or after heavy use / rainstorms
  • Brush walls and vacuum weekly to prevent algae growth
  • Inspect and clean the filter monthly — a dirty filter increases pump energy use by 25%

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Last Updated: Mar 26, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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