How to Calculate Pool Volume
Knowing your pool's volume in gallons is essential for accurate chemical dosing, filter sizing, heater selection, and saltwater system setup. The formula depends on your pool's shape — each shape has a slightly different volume calculation, all based on the same principle: area × depth × 7.48 (gallons per cubic foot).
Volume Formulas by Pool Shape
| Shape | Formula | Notes |
|---|---|---|
| Rectangular / Square | L × W × Avg Depth × 7.48 | Most common in-ground shape |
| Round / Circular | π × (D÷2)² × Avg Depth × 7.48 | Common above-ground shape |
| Oval | π × (L÷2) × (W÷2) × Avg Depth × 7.48 | Common above-ground, some in-ground |
| Kidney | 0.45 × (Wide + Narrow) × L × Avg Depth × 7.48 | APSP/PHTA standard formula |
Average Depth: How to Measure
For a pool with a gradual slope from shallow to deep end, average depth = (shallow end depth + deep end depth) ÷ 2. A pool with a 3.5 ft shallow end and 6.5 ft deep end has a 5 ft average depth. If your pool has a flat section that drops sharply (a "hopper" or "V-bottom"), the average is closer to 0.45 × (shallow + deep), which accounts for the smaller deep portion.
Pool Chemical Dosing Quick Reference
| Pool Size (gallons) | Shock (1 lb bags) | Salt (40 lb bags) to 3,200 ppm |
|---|---|---|
| 5,000 gal | 1 lb | 4 bags (133 lbs) |
| 10,000 gal | 1 lb | 7 bags (267 lbs) |
| 15,000 gal | 2 lbs | 10 bags (400 lbs) |
| 20,000 gal | 2 lbs | 14 bags (534 lbs) |
| 30,000 gal | 3 lbs | 20 bags (800 lbs) |
| 40,000 gal | 4 lbs | 27 bags (1,067 lbs) |
Pool Volume
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Chemical Dosing Tips
- Always add shock after sunset — UV breaks down chlorine; evening dosing lets it work overnight
- Run the pump 24 hours after shocking — circulation distributes chemicals evenly
- For salt pools, add salt in sections — pour along the edges, brush to help dissolve; run pump 24 hrs before testing level
- Recheck salt level after heavy rain — rainwater dilutes the pool, dropping ppm
- Test your water first — if the pool already has some salt or chlorine, dose for the difference, not the full amount
- Use a digital or strips-based pool test kit weekly during swim season to catch imbalances early
Frequently Asked Questions
Q: How many gallons is a 16×32 pool?
A: A 16×32 rectangular pool with a 5 ft average depth holds approximately 19,149 gallons (16 × 32 × 5 × 7.48). At 4 ft average depth it's 15,319 gallons; at 6 ft average depth it's 23,078 gallons.
Q: How do I calculate pool volume in gallons?
A: Multiply the pool's surface area by the average depth and then by 7.48 (gallons per cubic foot). For a rectangle: length × width × average depth × 7.48. For a circle: π × radius² × average depth × 7.48. Average depth for a sloped pool = (shallow end + deep end) ÷ 2.
Q: How much pool shock do I need?
A: Use 1 pound of calcium hypochlorite (68%) per 10,000 gallons for a standard maintenance shock. For an algae outbreak, triple the dose to 3 lbs per 10,000 gallons. Add after sunset and run the pump for 8 hours. Check chlorine with a test kit before swimming.
Q: How many bags of salt does a saltwater pool need?
A: To reach 3,200 ppm from fresh water, you need roughly 26.7 lbs of salt per 1,000 gallons (calculated as 3,200 ppm × 8.34 lbs/gal ÷ 1,000). For a 20,000-gallon pool that's about 534 lbs, or 14 bags of 40-lb salt. Add 1–2 bags at a time; retest before adding more.
Q: What is the average depth formula for a sloped pool?
A: For a pool with a simple slope from shallow to deep: average depth = (shallow + deep) ÷ 2. For a pool with a flat shallow area that drops sharply ("hopper bottom"), use 0.45 × (shallow + deep) instead — this accounts for the smaller proportion of truly deep water.