# Pool Shock Calculator

URL: https://speedycalculator.com/calculators/everyday-life/pool-shock/
Last updated: 2026-10-25

> The pool shock calculator works out how much liquid chlorine or calcium hypochlorite to add to reach breakpoint chlorination, from pool volume and your total and free chlorine readings.

## Inputs

- Pool volume (US gal, L, UK gal)
- Shock product
- Total chlorine (ppm)
- Free chlorine (ppm)

## Results

- Combined chlorine
- Chlorine to add (breakpoint)
- Amount of shock
- Metric amount

## Formula

```
Combined chlorine CC = total chlorine − free chlorine
Breakpoint dose (ppm) = 10 × CC − free chlorine
Liquid chlorine 12.5%: 10.7 fl oz per 10,000 gal per ppm
Cal-hypo 65–73%: 2.0 oz (weight) per 10,000 gal per ppm
```

## Explanation

Chloramines (combined chlorine) form when chlorine reacts with sweat, urine and debris; they cause the "pool smell" and eye irritation. Shocking to breakpoint – adding about ten times the combined chlorine – oxidises them. Shock in the evening with the pump running, and keep swimmers out until free chlorine falls below about 5 ppm.

### How to use the Pool Shock Calculator

- **Pool volume**
- **Shock product**
- **Total chlorine**
- **Free chlorine**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the pool volume, choose the shock product and enter your total and free chlorine test results.

### Tips

- Use the figures from your own bills and product labels – prices and appliance ratings vary widely.
- Look at yearly totals: small daily costs add up and make it easier to compare options.
- Round quantities up to whole packs, rolls or bulbs when you shop.
- Re-check the numbers when prices change; most results scale directly with the unit price.

### Common mistakes to avoid

- Confusing watts (power) with watt-hours or kilowatt-hours (energy).
- Comparing prices without bringing them to the same unit first.
- Ignoring one-off costs such as installation, delivery or replacement parts.

### Inputs explained

FieldWhat to enterPool volumeUnits: US gal, L, UK galShock productChoose one: Liquid chlorine (sodium hypochlorite 12.5%), Calcium hypochlorite (65–73%)Total chlorineIn ppmFree chlorineIn ppm

### What each result means

- **Combined chlorine** = max([Total chlorine] - [Free chlorine], 0)
- **Chlorine to add (breakpoint)** = max(10×[Combined chlorine] - [Free chlorine], 0)

### Example values

How the main result changes when **Pool volume** changes and everything else stays at the example values above:

Pool volume (US gal)Amount of shock (fl oz (liquid) / oz (granular))7,50060.211,25090.315,000120.418,750150.522,500180.630,000240.7

## Worked example

Inputs — Pool volume: 15,000 US gal; Shock product: Liquid chlorine (sodium hypochlorite 12.5%); Total chlorine: 3.5 ppm; Free chlorine: 2.5 ppm.

Results — Combined chlorine = 1 ppm; Chlorine to add (breakpoint) = 7.5 ppm; **Amount of shock = 120.4 fl oz (liquid) / oz (granular)**; Metric amount = 3,560 mL (liquid) / g (granular).

## FAQ

**How often should I shock my pool?**
Weekly in heavy use or hot weather, and whenever combined chlorine is above 0.2–0.5 ppm.

**How long after shocking can I swim?**
When free chlorine is back below about 5 ppm – usually 12–24 hours.

**Why use breakpoint chlorination?**
Adding about 10 × combined chlorine breaks down chloramines completely; less can make the smell worse.

**What formula does the Pool Shock Calculator use?**
Combined chlorine CC = total chlorine − free chlorine.


## Sources

- [U.S. CDC – Model Aquatic Health Code](https://www.cdc.gov/mahc/)