Pool Chlorine Calculator

A pool chlorine calculator tells you how much chlorine — liquid, cal-hypo shock or dichlor granular — to add to bring your free chlorine up to target, based on your pool's gallons. Pick your product type and it converts to the right amount, because each one is a different strength.

Your measurements

Result

Chlorine and shock are the season's repeat purchases, and over- or under-dosing is the most common pool mistake. Knowing your volume turns it into simple arithmetic — test, calculate, add, re-test.

How it is calculated

For each product, the dose per 10,000 gallons to raise free chlorine by 1 ppm is approximately: liquid 12.5% ≈ 10.7 fl oz; cal-hypo 73% ≈ 2 oz by weight; dichlor 56% ≈ 2.6 oz by weight. We scale by your volume and the ppm you want to raise. These are guides — product strengths and stabiliser levels vary, so always test.

Steps

Enter your pool volume in gallons.
Enter your current free chlorine from a test, and your target (2–4 ppm for normal sanitising).
Choose the product you're using — liquid, cal-hypo shock or dichlor.
Read the amount to add (fluid ounces for liquid, weight for granular).
Add with the pump running and re-test before swimming.

Worked example

To raise a 15,000-gallon pool from 0 to 3 ppm with liquid chlorine (12.5%), you'd add about 48 fl oz (roughly 6 cups).

Common questions

What free chlorine level should a pool be?

Usually 2–4 ppm for everyday sanitising. To shock a cloudy or algae pool, raise it to about 10 ppm.

Liquid, cal-hypo or dichlor — which?

Liquid is cheap for regular dosing; cal-hypo is a strong shock; dichlor is stabilised granular. The calculator doses whichever you pick.

How long before I can swim?

Wait until free chlorine falls back to about 4 ppm or lower — usually a few hours after a normal dose, longer after a shock.

Why does my chlorine disappear fast?

Sunlight burns off unstabilised chlorine and high bather load or algae consume it. Cyanuric acid (stabiliser) slows UV loss — but too much weakens chlorine.