Inputs used
Assumptions for this answer.
- Pool volume
- 20,000 gal
- Current free chlorine
- 1 ppm
- Target free chlorine
- 4 ppm
- Product
- 10% liquid chlorine
Pool answer
How much chlorine for a 20,000 gallon pool?
For a 20,000 gallon pool, raising free chlorine from 1 ppm to 4 ppm takes about 0.6 gal of 10% liquid chlorine.
Customize in the Pool Chlorine CalculatorAnswer table
Calculated result.
Free chlorine raise 3 ppm
10% liquid chlorine 0.6 gal
Pure chlorine equivalent 0.5 lb
Formula
The math behind this answer.
Liquid chlorine gallons = pool gallons x ppm increase x 0.00000834 / strength / 8.34
Substituted values
20,000 gal x 3 ppm x 0.00000834 / 0.10 / 8.34 = 0.6 gal
Source note
Chlorine answers use ppm increase, pool gallons, and labeled sodium hypochlorite strength. The dose math estimates product amount; CYA, sunlight, product age, and test accuracy affect the target and the result.
Scenario notes
Why this example may not match your pool exactly.
- A mid-size pool can use a meaningful amount of liquid chlorine, so label strength and storage age matter.
- This example uses a 3 ppm free chlorine raise, but the right target depends on CYA, swimmer load, sunlight, and whether the pool is already cloudy.
- For a mid-size residential pool, retesting after circulation is more reliable than stacking multiple chlorine corrections back to back.
Related calculators
Adjust the answer for your pool.
These answer pages use fixed assumptions. The calculators let you change gallons, readings, products, and targets.
Pool Chlorine Calculator Estimate how much liquid chlorine, bleach, or cal-hypo to add from pool gallons and your target free chlorine raise. Pool Stabilizer Calculator Estimate cyanuric acid stabilizer to add from pool gallons, current CYA ppm, and target CYA ppm. Pool Shock Calculator Estimate a shock dose from pool gallons, current free chlorine, target ppm, and product strength.
Answer FAQ
Common follow-up questions.
Use these answers to decide when the worked example is close enough and when to open the calculator.
How much 10% liquid chlorine raises a 20,000 gallon pool by 3 ppm?
About 0.6 gal in this example. Use the calculator if your target ppm increase or product strength is different.
Can I use bleach instead?
Only use plain, unscented sodium hypochlorite without splashless additives, fragrances, or cleaners, and enter the actual label percentage.
What if current chlorine is already above target?
Do not add more chlorine for that target. Circulate and retest until the reading returns to the range you are using.