How do you calculate a chemical dilution?

Divide the target working strength by the stock strength, then multiply by the final batch volume. For a 1% target from 12.5% stock in a 20 gal batch: 1 / 12.5 x 20 = 1.6 gal of concentrate, topped off with water to 20 gal.

How much water do I add?

Add water to bring the batch up to the final volume, not on top of the concentrate. If the calc says 1.6 gal of concentrate for a 20 gal batch, you add roughly 18.4 gal of water to reach 20 gal total.

What strength is liquid pool chlorine?

Commercial sodium hypochlorite is usually sold at 10% or 12.5% available chlorine, while household bleach is around 5-6%. Always enter the label strength, not an assumed value, because a 12.5% stock needs far less volume than a 10% stock.

Why does my mixed batch test weak?

Liquid chlorine loses strength with heat, light, and age, a 12.5% drum can drift to 10% or lower within a month or two. If your batch tests low, your real stock strength is below the label, so titrate the drum and re-run the dilution.

Can I use this for muriatic acid dilution?

Yes. Enter your target working acid percentage, the stock acid strength (commonly 31.45%, or about 20 Baumé), and the final volume. Always add acid to water, never water to acid, to control the exothermic reaction.

Is dilution ratio the same as parts per million?

No. This calculator returns a volume of concentrate for a percent working strength; ppm dosing (grams per volume of pool water) is a different calculation used to raise a residual by a set amount.

Pool, Spa & Water Treatment Chemistry calculator

Chemical Dilution Calculator

Chemical dilution tells a water treatment operator exactly how much concentrated stock, liquid chlorine, muriatic acid, or algaecide, to add to reach a specific working strength in a known batch volume. Pool techs, aquatics facility managers, and municipal operators run this every time they mix a day tank or top off a feed drum. Getting it right keeps residual chlorine in the safe 1-4 ppm band and stops you from over-buying concentrate or under-dosing a pool. The math is a straight proportion, but a small error in stock strength (12.5% vs 10% liquid chlorine) throws off the whole batch.

What this calculator does

Calculate dilution water needed from stock strength, target strength, and final batch volume.
Use it when preparing diluted cleaning, treatment, or test solutions from concentrated stock.
It computes how many gallons of a stronger stock chemical you must add to make a target working-strength solution at a given final batch volume.

Formula used

Concentrate needed = target strength / stock strength x final batch volume

Inputs explained

Target working strength: Use desired final concentration.
Stock chemical strength: Use label concentration of the stock product.
Final batch volume: Use the total desired working solution volume.

How to use the result

Use it when mixing day tanks, diluting muriatic acid, or preparing algaecide and feed solutions from a labeled concentrate.
It assumes the stock strength on the label is accurate and current; liquid chlorine degrades and loses several percent strength per month in heat, so verify with a titration for critical dosing.

Current U.S. benchmarks

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Common questions

How do you calculate a chemical dilution? Divide the target working strength by the stock strength, then multiply by the final batch volume. For a 1% target from 12.5% stock in a 20 gal batch: 1 / 12.5 x 20 = 1.6 gal of concentrate, topped off with water to 20 gal.
How much water do I add? Add water to bring the batch up to the final volume, not on top of the concentrate. If the calc says 1.6 gal of concentrate for a 20 gal batch, you add roughly 18.4 gal of water to reach 20 gal total.
What strength is liquid pool chlorine? Commercial sodium hypochlorite is usually sold at 10% or 12.5% available chlorine, while household bleach is around 5-6%. Always enter the label strength, not an assumed value, because a 12.5% stock needs far less volume than a 10% stock.
Why does my mixed batch test weak? Liquid chlorine loses strength with heat, light, and age, a 12.5% drum can drift to 10% or lower within a month or two. If your batch tests low, your real stock strength is below the label, so titrate the drum and re-run the dilution.
Can I use this for muriatic acid dilution? Yes. Enter your target working acid percentage, the stock acid strength (commonly 31.45%, or about 20 Baumé), and the final volume. Always add acid to water, never water to acid, to control the exothermic reaction.

Last reviewed 2026-05-12.