Pool Volume Calculator: The Complete Guide to Gallons, Fill Time, and Chemical Dosing
Knowing your pool's exact volume is essential for proper chemical treatment, equipment sizing, and water cost estimates. Too little chlorine leaves your pool vulnerable to algae and bacteria. Too much wastes chemicals and irritates skin and eyes. This guide covers how to calculate volume for every pool shape and translate that into practical maintenance numbers.
Pool Volume Formulas by Shape
Rectangular: L × W × Avg Depth × 7.48 = gallons
Round: Diameter² × Avg Depth × 5.9 = gallons
Oval: Long Axis × Short Axis × Avg Depth × 5.9 = gallons
Kidney/Freeform: (A+B) ÷ 2 × Length × Avg Depth × 7.48 × 0.85
Average Depth = (Shallow + Deep) ÷ 2
1 cubic foot = 7.48 gallons = 28.32 liters
Worked Example — 32×16 ft Rectangular Pool
Shallow end: 3.5 ft, Deep end: 8 ft
Average depth: (3.5 + 8) ÷ 2 = 5.75 ft
Volume: 32 × 16 × 5.75 = 2,944 cu ft
Gallons: 2,944 × 7.48 =
22,021 gallonsLiters: 22,021 × 3.785 =
83,350 litersFill time (8 GPM): 22,021 ÷ 8 ÷ 60 =
45.9 hoursWater cost ($5/1,000 gal):
$110Common Pool Sizes Reference
| Pool Type | Size | Avg Depth | Gallons |
|---|
| Above Ground Round | 15 ft dia | 4 ft | ~5,300 |
| Above Ground Round | 24 ft dia | 4 ft | ~13,500 |
| Small Inground | 12×24 ft | 5 ft | ~10,800 |
| Medium Inground | 16×32 ft | 5.5 ft | ~21,000 |
| Large Inground | 20×40 ft | 6 ft | ~36,000 |
| Hot Tub (round) | 7 ft dia | 3 ft | ~860 |
| Lap Pool | 10×50 ft | 4 ft | ~15,000 |
Chemical Dosing Basics
All chemical dosing is based on pool volume. Chlorine is the primary sanitizer: maintain 1–3 ppm free chlorine for pools, 2–4 ppm for hot tubs. pH should be 7.2–7.6 — low pH corrodes equipment, high pH reduces chlorine effectiveness. Alkalinity (80–120 ppm) buffers pH against rapid changes. Calcium hardness (200–400 ppm) prevents plaster etching. Cyanuric acid (30–50 ppm) stabilizes chlorine against UV degradation in outdoor pools.
Pro Tip — Shock Your Pool Weekly
Weekly shock treatment (super-chlorination to 10+ ppm) breaks down combined chlorine (chloramines) that cause the "chlorine smell" and eye irritation. Use 1 lb of calcium hypochlorite shock per 10,000 gallons. Shock at dusk — sunlight breaks down unstabilized chlorine rapidly. Don't swim until free chlorine drops below 5 ppm (usually 8-24 hours). After heavy rain, pool parties, or visible algae, shock immediately regardless of schedule.
Critical — Never Mix Pool Chemicals
Never mix different pool chemicals together before adding to water — some combinations (especially chlorine + acid, or different types of chlorine) produce toxic chlorine gas or explosive reactions. Add chemicals one at a time, wait 30 minutes between additions, and always add chemical to water (not water to chemical). Store chemicals in a cool, dry, ventilated area, separated by type. Wear gloves and eye protection when handling.