Pool Shock Calculator
Calculate the shock dose to reach a 10, 15 or 20 ppm free-chlorine shock level from your current level, volume and product type.
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What this tool does
Calculate the shock dose to reach a 10, 15 or 20 ppm free-chlorine shock level from your current level, volume and product type. A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
How to use the Pool Shock Calculator
- Enter or select pool volume in gal.
- Enter or select current free chlorine (ppm).
- Enter or select shock level.
- Enter or select shock product.
- Read the calculated result; change any measurement to compare alternatives.
Formula
dose = volume × (shock target − current FC) of available chlorine, divided by product strength; liquid shown in liters and fluid ounces
- volume
- Pool volume (gal, before metric conversion)
- current
- Current free chlorine (ppm)
- level
- Shock level
- product
- Shock product
A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
Worked example
For pool shock calculator, the following measurements illustrate the exact method: Pool volume: 15000; Current free chlorine (ppm): 2; Shock level: standard; Shock product: calhypo.
Inputs
- Pool volume15000 gal
- Current free chlorine (ppm)2
- Shock levelStandard / algae starting — target 15 ppm FC
- Shock productCal-hypo granules (65% available chlorine)
Result
- Shock product to add (grams)1,135.62
- Shock product to add (lb)2.5 lb
- Free chlorine increase needed (ppm)13
- Shock target (ppm FC)15
Results explained
- Shock product to add (grams)
- Shock product to add (grams) from the formula above. A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
- Shock product to add (lb)
- Shock product to add (lb) from the formula above, expressed in lb before metric conversion. A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
- Free chlorine increase needed (ppm)
- Free chlorine increase needed (ppm) from the formula above. A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
- Shock target (ppm FC)
- Shock target (ppm FC) from the formula above. A mode of the standard chlorine dosing math aimed at shock targets. Product strengths are the labelled typical values selected; check your product's available-chlorine percentage and adjust mentally if it differs.
Frequently asked questions
Enough chlorine product to lift free chlorine to the shock level for your situation — commonly about 10 ppm for routine weekly shocking, 15 ppm for visible algae starting, 20 ppm for heavy algae — minus the chlorine already in the water. This tool converts that ppm gap into a product dose for your volume.
Light 10 ppm, standard 15 ppm, heavy 20 ppm free-chlorine targets — the levels used in published pool-care guidance for routine, algae-start and heavy-algae shocking. Severe green pools may need the level held over repeated doses, not one giant dose.
The same available-chlorine math as the Pool Chlorine Calculator: required available chlorine (from volume × ppm gap) divided by the product's available-chlorine percentage — 65% for cal-hypo, 56% for dichlor, about 12.5% by volume for liquid chlorine.
At dusk or night — sunlight burns off unstabilized shock chlorine before it can work — with the pump running, and brush the surfaces first so algae is exposed.
Only after free chlorine falls back to the normal safe range on a fresh test and the water is clear. Follow the product label; this calculator does not determine safe swimming conditions.