Pool Volume & Chemical Calculator

How the math works

Everything starts with volume, because every dose scales with how much water is in the pool. Volume in gallons is the shape's area times the average depth times 7.48 — the number of gallons in a cubic foot. A rectangle is length × width × depth; a round pool is π × radius² × depth; an oval is π × (length/2) × (width/2) × depth. Use average depth: the mean of the shallow and deep ends, not the deepest point.

Once you know the gallons, the disclosed Free Chlorine and Total Alkalinity estimates scale from a specific product strength. A current EPA label works out to about 10.4 fl oz of 12.5% liquid chlorine per 1 ppm per 10,000 gallons. A current 73% cal-hypo label supports roughly 2 oz by weight for the same starting change, while current sodium-bicarbonate guidance uses 1.5 lb to raise Total Alkalinity by about 10 ppm. Verify the exact strength and amount against your product label before dosing.

pH is different: a pH delta does not translate into one universal acid or base dose. Total Alkalinity, CYA, borates, temperature, aeration, test error, and the product's formulation and strength all change the response. The calculator therefore reports only whether pH needs to move up, down, or not at all. Use the exact current product label and pool volume, start with no more than half of the label-calculated amount, follow its circulation interval, and retest before adding more.

The order matters

Balance in this order: Total Alkalinity first, then pH, then chlorine. Alkalinity is the buffer that keeps pH from bouncing, so correcting it first makes the pH adjustment stick. Chlorine works best with pH in the 7.2–7.8 range — at high pH a chunk of your chlorine is chemically unavailable, so chasing FC before fixing pH wastes product. The calculator gives all three at once, but apply them over a day or two, not in one dump.

Common mistakes

• Using deepest depth instead of average. A pool that's 8 ft at the deep end but averages 5 ft has 60% less water than the deep number implies — overdosing follows.
• Trusting test strips for chlorine. Strips are fine for a quick glance but too coarse for dosing. A drop-based kit (FAS-DPD) is worth it.
• Turning a pH difference into a universal dose. pH demand is nonlinear. Use the exact product label, begin with no more than half of its calculated amount, circulate for the label-specified interval, and retest.
• Ignoring cyanuric acid. CYA (stabilizer) changes how much Free Chlorine you actually need to hold. This tool does not model it — if you run stabilized chlorine or tabs, follow a CYA-adjusted FC target.

When this calculator is the wrong tool

This covers pool volume plus starting estimates for the stated chlorine and alkalinity product strengths. Its pH result is direction-only. It does not size salt for a saltwater chlorine generator, handle bromine spas, model calcium hardness or CYA reduction, or diagnose cloudy water and algae blooms. For those, follow the exact product and equipment manuals or a qualified pool professional.

Volume is plain geometry. Chlorine and alkalinity amounts are product-strength-specific planning estimates. pH is direction-only; verify every treatment against the exact current product label. CYA/stabilizer interactions are not modeled.