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 chemical doses are simple ratios. Pool-care rules of thumb are published per 10,000 gallons, so the calculator scales each one by your volume ÷ 10,000. To raise Free Chlorine, about 10.7 fl oz of 12.5% liquid chlorine adds 1 ppm per 10,000 gallons (or roughly 2 oz of 73% cal-hypo by weight). To raise Total Alkalinity, 1.5 lb of baking soda adds about 10 ppm. For pH, soda ash raises it (~6 oz per 0.2) and muriatic acid lowers it (~10.7 fl oz per 0.2). The calculator picks the right pH chemical based on whether your current reading is below or above target.

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.
• Dosing the full amount at once. Add about half, circulate, wait, and retest. Adding more is easy; pulling chemicals back out is not.
• 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 chlorine pools and the four everyday chemicals. 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 (those need a shock-and-circulate routine plus filtration, not a one-shot dose). For those, follow your equipment manual or a full pool-care guide.

Dose rates are standard pool-industry rules of thumb (per 10,000 gal); verify against your product label. CYA/stabilizer interactions not modeled. Volume is plain geometry.