Pool Calculator
A 16×32 ft rectangular pool averaging 5 ft deep holds 19,200 gallons. Fill time: ~32 hours with a garden hose. Annual operating cost: $1,200-3,600.
Pool Calculator
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How to Calculate Pool Volume
The formula for a rectangular pool:
gallons = length_ft × width_ft × avg_depth_ft × 7.48
The constant 7.48 converts cubic feet to US gallons.
For round pools: gallons = π × radius² × avg_depth × 7.48
For oval pools: gallons = π × (length/2) × (width/2) × avg_depth × 7.48
| Pool Size | Avg Depth 4 ft | Avg Depth 5 ft | Avg Depth 6 ft |
|---|---|---|---|
| 12×24 ft | 8,602 gal | 10,752 gal | 12,902 gal |
| 16×32 ft | 15,360 gal | 19,200 gal | 23,040 gal |
| 18×36 ft | 19,440 gal | 24,300 gal | 29,160 gal |
| 20×40 ft | 23,936 gal | 29,920 gal | 35,904 gal |
| 15 ft round | 5,310 gal | 6,637 gal | 7,965 gal |
| 24 ft round | 13,594 gal | 16,992 gal | 20,390 gal |
| Chemical | Amount | Purpose |
|---|---|---|
| Chlorine (granular) | 2 oz | Initial sanitization |
| pH increaser (soda ash) | 6 oz per 0.2 pH rise | Balance pH (7.2-7.6) |
| Alkalinity increaser | 1.5 lbs per 10 ppm rise | Buffer pH stability |
| Cyanuric acid (stabilizer) | 13 oz per 10 ppm | Protect chlorine from UV |
| Calcium hardness increaser | 1.25 lbs per 10 ppm | Prevent plaster etching |
Common Mistakes:
- Using maximum depth instead of average depth — overestimates volume by 30-40%
- Forgetting to account for pool shape — kidney and L-shaped pools have less area than the bounding rectangle
- Over-chlorinating based on incorrect volume — causes skin irritation and equipment corrosion
- Sizing the pump for the pool volume without accounting for turnover rate — the pump should circulate the entire volume every 6-8 hours
Frequently Asked Questions
How many gallons of water are in my pool?
Multiply length × width × average depth × 7.48 for rectangular pools. A 16×32 ft pool with 5 ft average depth holds 19,200 gallons. For round pools, use π × radius² × depth × 7.48. A 24-ft round pool at 4 ft deep holds about 13,594 gallons.
How long does it take to fill a pool?
A standard garden hose delivers 5-10 gallons per minute (300-600 gallons per hour). A 20,000-gallon pool takes 33-67 hours to fill. A fire hydrant fill service ($200-500) can fill it in 1-3 hours. Municipal water cost: $30-100 depending on your local rate.
How much does it cost to maintain a pool annually?
Annual pool costs: chemicals $300-800, electricity (pump/filter) $600-1,200, water replacement $100-300, equipment maintenance $200-500, professional cleaning $1,200-2,400 if hired. Total: $1,200-3,600/year for DIY maintenance, $2,400-5,000 with a pool service.
What size pool pump do I need?
The pump must circulate the entire pool volume in 8 hours or less. For a 20,000-gallon pool: 20,000 ÷ 8 hours ÷ 60 minutes = 42 GPM minimum flow rate. A 1.5 HP pump typically delivers 60-80 GPM — adequate for most residential pools up to 25,000 gallons.
How do I calculate average pool depth?
Add the shallow-end depth and deep-end depth, then divide by 2. For a pool that's 3 ft shallow and 8 ft deep: (3+8)/2 = 5.5 ft average. For pools with a large shallow area and small deep end, use a weighted average or split into two sections.
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