Testing the chlorine percentage of your bleach


Bronze Supporter
Jul 6, 2017
Kinston, NC
This year has been a different year since bleach has been problematic due to COVID. I bought a barrel of bleach which was "10-15%" bleach and cut it 1:1 with water. Now after a couple of months, I don't know the concentration. Searching this site, I found an old thread stating that you could put 0.1mL of your unknown bleach in 1 liter of water (nonchlorinated) and then test. I was a bit skeptical and decided to go the math. Mine tested 6%.

Units for FC are ppm or mg/L

Assuming 6% chlorine -

6%=6g chlorine/100g water
Since water density ~1mg/mL, this equals 6g chlorine /100mL water
Convert go mg: 6000mg chlorine /l00mL water
1mL of 6%=60mg chlorine
0.1mL of 6%=6mg chlorine

Adding 0.1mL of 6% bleach to 1L water = 6mg chlorine /1 L water

So mathematically this works out. The bleach that I'm using is 6%.

An insulin syringe can be used to measure the small quantity of bleach needed for the test. They come in 0.3, 0..5, and 1mL syringe sizes. You must use nonchlorinated water. Your tap water may be chlorinated.
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