For best results and the least amount of waste, poke a hole with a ball point pen in the vented little circle in the liner of your detergent bottle. Then pour detergent through this tiny hole for the least mess. Don't forget to wipe off the cap and any drips on the dirty clothes you're about to wash. No waste, no mess!
Two capfuls of detergent is all you need for a full load of laundry - really! More detergent will not make laundry cleaner and only wastes the detergent.