How Much Chlorine to Add to a Pool
There is no single answer — the right amount depends on your pool size, your current chlorine level, and how much stabiliser is in the water. Here is how to work it out.
The target: 1–3 ppm free chlorine
Free chlorine is the active chlorine available to sanitise your pool. Levels are measured in ppm (parts per million). The standard target for a residential pool is 1–3 ppm.
If your stabiliser (cyanuric acid, or CYA) level is high, you need more chlorine to stay effective. At a stabiliser level of 80 ppm you need at least 6 ppm free chlorine just to maintain sanitation — not the usual 1–3. More on stabiliser levels →
What affects the dose
Pool volume
A larger pool needs more chemical to raise the concentration by the same amount. Measure your pool dimensions and calculate volume first.
Calculate your pool volume →Current chlorine level
Test your water first — the dose is the difference between where you are and the target, scaled to your pool size.
Scan your test strip →Stabiliser (CYA) level
Higher stabiliser means you need a higher chlorine target. If your stabiliser is above 50 ppm, the "normal" 1–3 ppm target no longer applies.
Product concentration
Liquid chlorine is typically 10–12% available chlorine. Cal-Hypo granules are around 65%. The dose calculation depends on which product you use.
Choosing a product
Liquid chlorine (10%)
The simplest option. Pour near a return jet with the pump running. Fast-acting, no residue. Does not raise stabiliser levels.
Granular Cal-Hypo (65%)
More concentrated — you need less product by weight. Pre-dissolve in a bucket of water before adding to avoid bleaching the pool surface. Does not raise stabiliser levels.
Always add Cal-Hypo granules to water — never pour water onto granules. Adding water to Cal-Hypo can cause a violent reaction. Stir gently.
Trichlor tablets (slow-release)
Convenient for day-to-day maintenance in a floater, but they release chlorine slowly — not useful for correcting a low reading quickly. Each tablet also adds stabiliser over time, which can become a problem at high doses. Test stabiliser levels monthly if you rely on tablets.
A worked example
Pool: 15,000 gallons · Current chlorine: 0.5 ppm · Target: 2 ppm
Shortfall: 1.5 ppm × 15,000 gal ÷ 10,000 × 12.8 fl oz ≈ 29 fl oz liquid chlorine (10%)
The 12.8 fl oz constant is calibrated for 10% liquid chlorine, verified against PoolMath.
This is illustrative. Use PoolScan for an accurate dose based on your actual numbers.
After adding chlorine
- 1Keep the pump running for at least 4 hours to circulate the chemical.
- 2Retest after circulation — do not add more chlorine without retesting first.
- 3Wait until chlorine is in the normal range before swimming — typically 1–3 ppm for pools with CYA below 50 ppm. If your CYA is higher, your normal FC target is also higher, and it is safe to swim at that level as long as it is below your shock target.
- 4If you have shock-dosed the pool, wait until FC has dropped well below the shock target. For low-CYA pools (under 50 ppm), below 5 ppm is a safe guideline — this can take up to 24 hours.
Enter your pool volume and current readings — PoolScan calculates the exact dose and tells you how to apply it.
Calculate your chlorine dose →Shop on Amazon
Buy Liquid Chlorine
Buy on Amazon
Buy Cal-Hypo
Buy on Amazon
Chlorine Tablets
Buy on Amazon
Test Strips
Buy on Amazon
Affiliate links — we may earn a small commission at no cost to you.