The manufacturers of detergent always recommend the HIGHEST amount to get clothing clean. Its called "marketing". Modern cloth diapers are easy to clean due to their fabrics—and are most usually washed in relatively small loads. So, not much detergent is needed.

If you are using a mainstream commercial detergent, then a good rule of thumb is if the bottle recommends you use 1/4 cup—then use 1/4 of that amount. If you find your laundry to be very bubbly and sudsy, this is not good. Cut the detergent down again. Front loaders will require even less detergent. So rule of thumb —start with 1/4 of the recommendation on the bottle of your choice, and move up from there if they are not getting clean enough.

If you are using a detergent specifically made for cloth diapers you should be okay following the direction on the label or taking 1/2 the recommended amount and adjust from there if necessary. Remember, excess suds means it's harder to get your diapers rinsed completely clean. And any left over residues of any kind can cause repelling issues.