2oz. per 10 heavily soiled towels. [size doesn’t matter, no pun intended]
2oz. per 20 towels max if they’re not really soiled. [for example your wash mitts & drying towels]
If you’re doing a large load [30 towels] of heavily soiled towels [for example towels you’ve used for rinseless/waterless washing or interior cleaning] you want to go 2oz. per 10 towels + another 2oz. for good measure.. So if I’m doing a load of 30 heavily soiled towels I use 8oz. of Towel Kleen/water level Extra Large/Hot water/Regular speed agitation in a top loading traditional washer.
Allow for a bit of water to run and then add the detergent in order to create good suds before putting your towels into the washer.
Tumble dry on low for 30 min.
[if your towels are Super Dirty, for example grade F towels, running them through the washer a 2nd time immediately after the 1st cycle is Completely done really helps them get alot cleaner]
That’s what I do and what I recommend for best results with 3D Towel Kleen.