18x36 Rectangular Pool Volume Calculator
Standard In-Ground Medium-Large Pool Capacity (22,000–26,000 Gallons)
An 18x36 rectangular pool with an average depth of 4.5 feet holds approximately 21,870 gallons (82,780 liters). Pools with an 8-foot diving well hold up to 26,730 gallons. Calculate your exact water capacity and chemical balance below.
Water Capacity Dashboard
Adjust average water depth if your pool has a different wall height.
18x36 Pool Chemical Startup Guidelines
• Baseline Salt (3,200 ppm): ~584 lbs (15 forty-pound bags)
• Weekly Shock: 2 to 3 one-pound bags of 73% Cal-Hypo shock or 1.7 gallons of liquid chlorine.
• Muriatic Acid to Lower pH by 0.4: ~34 fl oz of 31.45% muriatic acid.
Turnover & Pump Sizing for 18x36 Pools
With ~22,000 gallons, an 18x36 pool requires an 8-hour turnover rate of at least 46 GPM (gallons per minute). A 1.5 HP variable-speed pump is ideal to save energy while maintaining sparkling water.