Pool Shock Calculator: How Much Shock Does My Pool Need?

In-ground swimming pool
Photo: imageBROKER/Perry Mastrovito / imageBROKER / Getty Images
In-ground swimming pool
Photo: imageBROKER/Perry Mastrovito / imageBROKER / Getty Images
Highlights
  • The amount of shock you need for your pool depends on its volume and water condition. 

  • You typically need one pound of shock per 10,000 gallons of water. 

  • Add more if your pool is combating algae growth.

  • The average cost of pool shock is $5 to $15 per pound.

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Shocking a pool eliminates chloramines, algae, bacteria, and other contaminants. It does this by elevating the available free chlorine level to 10 times or more the level of combined chlorine.

How much shock does my pool need? It's an excellent question to ask, as it eliminates guesswork and potentially saves both money and time. The answer depends on the size of your pool, the condition of the water, and the current levels of combined chlorine. 

How Much Pool Shock Do I Need 

Guidelines suggest your pool needs one pound of pool shock for every 10,000 gallons. However, there are several factors to consider when determining precisely how much your pool needs at any given time. 

There are several types of pool shock available, each with its own recommended amounts, depending on your goal. The exact amounts will be listed on the product packaging. 

Pool Size (gallons)Pool shock for regular maintenance (lbs.)Pool shock for light algae growth (lbs.)Pool shock for heavy algae growth (lbs.)
5,0000.510.75–2
10,000123–4
15,0001.534.5–6
20,000246–8
How much shock your pool needs by algae condition, with dark green algae needing 3x shock

How to Calculate Pool Shock Amount

The first step to calculating how much shock your pool needs is determining the current water condition. Use test strips or a liquid testing kit (you can purchase either one from your local pool supply store or home improvement store) on your pool water and subtract the free chlorine amount from the total chlorine amount. Use the result, which is the combined chlorine level, to check the recommendations on the specific pool shock product you're using. 

Next, convert that number by calculating it against the volume of water in your pool. That result is how much shock your pool needs.

Pounds of Shock = Pool Volume Gallons / 10,000

How to Measure Your Pool Volume

Man pouring liquid chlorine into swimming pool
Photo: slobo / iStock / Getty Images Plus / Getty Images

Measure the volume of a constant-depth rectangular pool by measuring one short side, one long side, and the depth. Multiply these values together. Multiply that value by 7.5 to convert cubic feet to gallons.

How to Measure Pool Volume with Varying Depths

For pools with a shallow end, a deep end, and a continuously sloping bottom, multiply the length and width by the average depth and then by 7.5. 

How to Measure the Volume of Round Pools

To measure the volume of a circular pool, measure the diameter, from one side to the other.  Divide the diameter by two to get the radius. Square the radius and multiply it by 3.14. Multiply the result by the depth and by 7.5 for the total volume. 

How to Measure the Volume of Irregular Pools

To determine the volume of irregular pools, determine the volume of each section separately. For example, if you have a sloping bottom in one part of the pool and constant depth in another, determine the volume of each space first. Add the volumes together for the total pool volume. 

Who to Hire to Shock Your Pool

Continuous maintenance is necessary when you own a pool. Shocking your pool regularly is essential to keep the water quality in swimmable condition. While shocking your pool is straightforward, it's just one task of many on a pool maintenance checklist

For that reason, many homeowners hire a local pool service to manage the week-to-week tasks to make sure their pool stays in optimal condition. 

Frequently Asked Questions

Pool shock and chlorine have similar chemical compositions, but are entirely different products with different uses. Pool chlorine is necessary for day-to-day water maintenance. It kills germs, bacteria, and contaminants. Pool shock also does this, but goes a step further and eliminates the chloramines left over from regular maintenance.

You can put too much shock in a pool. Following the directions on the shock product you're using is crucial. Using too much shock can make the water cloudy, have adverse effects on pool users, damage the pool equipment or the pool itself, and even encourage particular types of algae to grow. 

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