You will hear a lot about watering when the pots are 'light'. Well, what is light to a 20 year old, might not be light for a 70 year old, so this is what I did.
I weighed my 5 gallon fabric pot, with Cana Coco and 1/3 Perlite by volume when it was 'bone dry'. It weighed 5 1/2 lbs. (on the raggedy old scale I am using).
I watered it so that it wouldn't hold any more and it weighed 21 1/2 lbs. dripping wet (on the same raggedy old scale)
I concluded that the pot could hold 16 lbs. of water (which may or may not be right because of the raggedy old scale.
Cana defines a "light" pot as one that has used 1/2 of the water it is capable of holding.
So, when my plants get to 14 lbs. I water them and be sure go get the runoff I want. I am getting used to what that 14 lb. pot feels like when I lift it up, so I won't need the scale too long, but it is working well.
Just my 2c.