Add salt with the pump running, brush it to dissolve, and wait 24 hours before retesting. Use pure pool salt (sodium chloride, at least 99%).
How pool volume is calculated
PoolVolume multiplies the surface area by the average depth. Rectangle: length × width. Round: π × (diameter ÷ 2)². Oval: π ÷ 4 × length × width. Kidney: 0.45 × (wide end + narrow end) × length, a common estimate for free-form pools. Cubic feet × 7.48 gives US gallons; cubic metres × 1,000 gives litres.
Round above-ground pools (46 in of water)
| Diameter | US gallons |
|---|---|
| 12 ft | 3,240 |
| 15 ft | 5,070 |
| 18 ft | 7,300 |
| 21 ft | 9,930 |
| 24 ft | 12,970 |
| 27 ft | 16,420 |
| 30 ft | 20,270 |
How chemical doses are calculated
One ppm is one milligram per litre, so the grams of active chemical needed are the ppm increase × litres ÷ 1,000. That is divided by the product's strength. Alkalinity is measured as calcium carbonate, so baking soda doses use the ratio of their equivalent weights (84 ÷ 50); calcium chloride doses use 111 ÷ 100 and the product's purity.
Amount for 10,000 US gallons
| Product | Raises by | US | Metric |
|---|---|---|---|
| Liquid chlorine 12.5% | 1 ppm | 10.2 fl oz | 303 mL |
| Liquid chlorine 10% | 1 ppm | 12.8 fl oz | 379 mL |
| Household bleach 6% | 1 ppm | 21.3 fl oz | 631 mL |
| Cal-hypo shock 65% | 1 ppm | 2.1 oz | 58 g |
| Dichlor granules 56% | 1 ppm | 2.4 oz | 68 g |
| Trichlor tablets 90% | 1 ppm | 1.5 oz | 42 g |
| Stabilizer (cyanuric acid granules) | 10 ppm | 13.4 oz | 379 g |
| Baking soda (sodium bicarbonate) | 10 ppm | 1.4 lb | 635 g |
| Calcium chloride 77% (dihydrate flakes) | 10 ppm | 1.2 lb | 545 g |
| Pool salt (sodium chloride) | 100 ppm | 8.35 lb | 3.79 kg |
Estimates by mass balance; products vary in strength and liquid chlorine weakens with age and heat. Add chemicals in stages, never mix products together, follow each label's safety directions and retest. Typical targets are general guidance; follow your test kit, pool surface and equipment manufacturer.
Frequently asked questions
How many 40 lb bags of salt do I need?
Divide the pounds by 40 and round up. A 20,000 gallon pool going from 0 to 3,200 ppm needs about 534 lb, so 14 bags.
How much salt raises 10,000 gallons by 100 ppm?
About 8.35 lb (3.8 kg).
What if I add too much salt?
Salt does not evaporate; the only way to lower it is to drain some water and refill.
Is PoolVolume free?
Yes, with no sign-up or ads.
Are my pool details saved?
Yes, in this browser only.