How much would be a small amount, say, for a full (but not super) laundry load?
Part of why you have to experiment, say with a load of towels or a load jeans, is that if your water is super soft you may require less than if your water is hard.
DAWN also works super well for hand washing delicate items.
If you have a front loader, first try ONE tablespoon, and if you aren't satisfied with the results, then try two. With a top loader, I think I'd experiment with sheets, and start out with 3 tablespoons.
IF that is too much, it would be pretty easy to rinse out sheets -- as opposed to towels or blue jeans which are so bulky.