Pool shock calculator: find how much shock to add to your pool from its volume, current free chlorine and shock type, with examples for 1,000 to 30,000 gallon pools. Enter the values shown in the calculator to get a practical planning estimate.
Free interactive calculatorWater Chemistry
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FREE ONLINE CALCULATOR
Pool Shock Calculator
Estimate the amount of chlorine-based shock needed to raise free chlorine by a selected amount.
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YOUR ESTIMATE
Estimated shock amount
Planning estimate
Shock product—product
Available chlorine—pounds of available chlorine
Fluid or weight detail—approximate
Free-chlorine increase—ppm
Important: Shock products are not interchangeable. Follow the exact label for application, circulation and re-entry, and never mix shock with acids or other chemicals.
ABOUT THIS TOOL
What this calculator helps with
Water Chemistry
The pool shock calculator estimates how much chlorine-based shock to add to raise free chlorine from the current reading to your target. It supports common liquid and granular strengths, including 10% and 12.5% liquid chlorine, 65% and 73% cal-hypo and 56% dichlor, and shows the available chlorine behind the estimate.
Why this calculation matters
Shock products come in different strengths and formulations, so the same pool can need very different amounts of product. Tying the dose to the exact available-chlorine percentage on your label avoids treating every shock product as though it were the same.
Details to have ready
Pool volume and how accurate that estimate is.
The exact shock product and its available-chlorine percentage.
Whether the product is liquid or granular, and the product density for a liquid conversion.
Your current free-chlorine level and the target you are aiming for.
The application and re-entry directions printed on the product label.
How to prepare
Confirm the pool volume in gallons or litres.
Test the current free-chlorine level.
Choose the shock product and enter the strength from its label.
Calculate, apply as the label directs, circulate and retest before swimming.
Note: Never mix pool shock with acids or other chemicals. Product labels take priority over an online estimate.
CALCULATION GUIDE
How pool chlorine calculations work
The calculator first finds the amount of available chlorine needed for the selected free-chlorine increase, then converts that amount into your chosen product.
Available chlorine (lb) ≈ Pool volume (gallons) × Chlorine increase (ppm) ÷ 120,000 Product needed (lb) = Available chlorine ÷ (available chlorine % ÷ 100)
Liquid chlorine is also converted to an approximate fluid volume using the product density you enter. For tablets, the calculator uses the actual tablet weight and available-chlorine percentage. This makes phrases such as how much liquid chlorine to add, how much granular chlorine to use, and how many chlorine tablets to use part of the same transparent calculation.
Why product strength matters
A 12.5% liquid product does not contain the same amount of available chlorine per pound as a 6% product, and granular products use different available-chlorine strengths. Always enter the strength from the exact package you are using.
POOL SHOCK CHART
How much shock to add by pool size
The chart shows the shock needed to raise free chlorine by 10 ppm, a common example increase, for pools from 1,000 to 30,000 gallons. It covers questions such as how much shock for a 6,000 gallon pool or a 1,000 gallon pool. Your own increase depends on the current reading, the target and the problem you are treating.
Pool shock chart: product needed to raise free chlorine by 10 ppm
Pool size (US gal)
Available chlorine
65% cal-hypo
73% cal-hypo
12.5% liquid
10% liquid
1,000
0.08 lb
2.1 oz
1.8 oz
9 fl oz
11 fl oz
2,000
0.17 lb
4.1 oz
3.7 oz
17 fl oz
21 fl oz
6,000
0.50 lb
12.3 oz
11.0 oz
51 fl oz
64 fl oz
10,000
0.83 lb
20.5 oz
18.3 oz
85 fl oz
107 fl oz
15,000
1.25 lb
30.8 oz
27.4 oz
128 fl oz
160 fl oz
20,000
1.67 lb
41.0 oz
36.5 oz
171 fl oz
213 fl oz
30,000
2.50 lb
61.5 oz
54.8 oz
256 fl oz
320 fl oz
Liquid amounts assume a product density of 10 lb per gallon, as in the calculator. Always use the strength on your own label, and enter your actual current and target chlorine in the calculator.
Shocking small pools
For a 1,000 gallon pool a 10 ppm increase needs only about 2 oz of 65% cal-hypo or 8.5 fl oz of 12.5% liquid chlorine. Small pools react quickly to small mistakes, so weigh or measure the product carefully and follow the label.
Liquid, cal-hypo and dichlor shock
Liquid chlorine: quick and leaves no calcium or stabilizer, but the strength varies by product.
Cal-hypo (65% or 73%): a strong granular shock that adds calcium.
Dichlor (56%): a granular shock that also adds stabilizer (cyanuric acid).
Branded shocks such as HTH are covered by entering the available-chlorine percentage on the label. For routine chlorine dosing rather than shock, use the pool chlorine calculator.
COMMON QUESTIONS
About Pool Shock Calculator
How much shock do I need for my pool?
It depends on pool volume, the current free-chlorine reading, the target level and the strength of the shock. Raising free chlorine by 10 ppm takes about 0.83 lb of available chlorine per 10,000 gallons, which is roughly 20 oz of 65% cal-hypo or 85 fl oz of 12.5% liquid chlorine. Enter your own numbers in the calculator.
How much shock for a 6,000 gallon pool?
To raise free chlorine by 10 ppm in 6,000 gallons you need about 0.5 lb of available chlorine. That is roughly 12 oz of 65% cal-hypo or about 51 fl oz (0.4 gallon) of 12.5% liquid chlorine. Your own reading and target will change the figure, so enter them and check the product label.
How much shock for a 1,000 or 2,000 gallon pool?
For a +10 ppm increase, a 1,000 gallon pool needs about 2 oz of 65% cal-hypo or 8.5 fl oz of 12.5% liquid chlorine. A 2,000 gallon pool needs about 4 oz of 65% cal-hypo or 17 fl oz of 12.5% liquid. Small pools react quickly to small errors, so measure carefully and follow the label.
How much chlorine to shock a pool?
Enter the volume, current free chlorine and target, then choose the product. The calculator turns the free-chlorine increase into product by weight, and into approximate volume for liquid chlorine using the density you enter. See the shock chart on this page for common pool sizes.
How much liquid chlorine should I use to shock a pool?
Choose a liquid chlorine strength, such as 10% or 12.5%, and enter the current and target free chlorine. A 15,000 gallon pool raised by 10 ppm needs about 128 fl oz (1 gallon) of 12.5% liquid chlorine, or about 160 fl oz of 10%. Always check the strength printed on your bottle.
How much granular chlorine is needed for a pool shock?
Choose the granular product strength shown on the label. For a 15,000 gallon pool and a 10 ppm increase, 65% cal-hypo needs about 31 oz and 73% cal-hypo about 27 oz. The calculator works this out for your own volume and target.
Can I use this for HTH or other branded shock?
Yes. Use the available-chlorine percentage printed on the product, not the brand name. If the strength is not in the list, choose Custom available chlorine strength and enter the percentage from the label.
What free chlorine target should I use when shocking?
It depends on why you are shocking and on your stabilizer (cyanuric acid) level. Routine shock and treating algae use different targets, so check the product label and the guide to clearing a green pool before choosing the target.
When can I swim after shocking a pool?
Follow the re-entry directions on the product label and wait until your free chlorine has fallen back into the normal range on a fresh test. Do not rely on a fixed number of hours.
Can I use a swimming pool shock calculator for a pool measured in litres?
Yes. Change Volume units to litres and the calculator converts the volume. Choose the product strength shown on your label, or use the Custom option to enter it.
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