Pool Shock Calculator
Find out exactly how much shock product to add to raise your free chlorine to shock level. Pick your shock type, enter your pool volume and current/target chlorine, and get a precise dose in ounces, pounds and (for bleach) fluid ounces.
How the math works
One gallon of water weighs 8.34 pounds, so the pure chlorine needed to raise ppm is:
- Pure chlorine (lbs) = (Target ppm − Current ppm) × Gallons × 8.34 ÷ 1,000,000
- Product (lbs) = Pure chlorine ÷ Available chlorine fraction
- Cal-Hypo 65% → divide by 0.65 · Lithium 35% → divide by 0.35 · Bleach 10% → divide by 0.10
- For liquid bleach: fluid ounces = product lbs × 16 ( bleach weighs about 1 lb per 16 fl oz, like water)
Example: a 12,000-gallon pool going from 2 to 10 ppm needs (10−2) × 12,000 × 8.34 ÷ 1,000,000 = 0.80 lb pure chlorine. With Cal-Hypo 65%: 0.80 ÷ 0.65 = 1.23 lb (~20 oz). With 10% bleach: 0.80 ÷ 0.10 = 8.0 lb (~128 fl oz, about 1 gallon).
Which shock should you use?
- Cal-Hypo (65–73%): fastest dissolving granular shock, no cyanuric acid added. Raises calcium hardness slightly — fine for most pools, watch it on already-high CH plaster pools. Best all-purpose pool shock.
- Lithium Hypochlorite (35%): granular, dissolves instantly, leaves no residue. Great for vinyl liners and fiberglass pools where cal-hypo dusting is a concern. Pricier per pound but very clean.
- Liquid Bleach (10–12.5%): pours in and disperses in seconds, adds only a trace of salt. Cheapest per ppm at pool-store concentrations. Best for daily/weekly dosing and for pools where you must avoid adding calcium or CYA.
For routine maintenance dosing (not full shock), see our chlorine dose calculator. To compare the trade-offs of each chlorine type in depth, read our chlorine types compared guide. Don't know your pool size? Start with the pool volume calculator.
Tips before you shock
- Shock at dusk. Sunlight burns off free chlorine fast — by morning your shock level can drop 50%+ with no CYA protection.
- Brush and run the pump. Brushing lifts algae off surfaces so chlorine can kill it; keep the pump running 24/7 during a treatment.
- Pre-dissolve cal-hypo for vinyl/fiberglass. Granules that sit on a liner can bleach a permanent ring. Mix in a bucket first, then pour around the perimeter.
- Don't mix products. Never add cal-hypo and trichlor to the same water at the same time — they react and can release dangerous gas. Wait at least 24 hours between different shock types.
- Re-test the next morning. You want FC to still be above your minimum for your CYA level. If it dropped to zero, repeat the shock dose.
Frequently asked questions
How much cal-hypo does it take to shock a 10,000 gallon pool?
From 2 ppm to 10 ppm (an 8 ppm rise) in 10,000 gallons needs about 1.03 lb of 65% cal-hypo — roughly 16 oz, or one standard 1-lb shock bag is plenty. Use the calculator above for your exact numbers.
How much bleach equals one bag of cal-hypo shock?
One 1-lb bag of 65% cal-hypo delivers 0.65 lb of pure chlorine. You'd need about 6.5 lb of 10% bleach — roughly 100 fl oz, or just under a gallon — to deliver the same amount of chlorine. Bleach is usually cheaper per ppm at pool-store prices.
What chlorine level should I shock to?
The shock level depends on your cyanuric acid (CYA) reading. A common rule of thumb is to reach about 30% of your CYA level. With CYA at 30 ppm, shock to ~10 ppm; with CYA at 50 ppm, shock to ~15 ppm. Use the CYA calculator to dial in your stabilizer first.
Can I use this for an algae green pool?
Yes — for a green pool you'll typically shock to 10–15 ppm and brush twice a day until the water clears. Run the pump 24/7. See our algae treatment guide for the full kill order.
Does bleach expire?
Yes. Liquid bleach loses strength quickly — about 20% in 6 months and faster in heat. Old bleach bought from a big-box store may already be down to 6%. If your bleach isn't fresh, treat it as 6% in the calculator (or just use the chlorine calculator's bleach presets).