Your everyday laundry detergent should be a tough, all-fabric cleaner that does as well on a baby's burp cloths and leaky diaper stains as it does on his big brother's baseball uniform. 
But how do powder detergents and laundry liquids differ from one another? More importantly, which one is right for you and your washday loads and laundry stains?
The information and tips below can help you make a smart, effective choice that will get your everyday wash clean and effectively remove those occasional tough stains.
the laundry detergent differences between liquid and powder.

Choose the laundry detergent type that works best on the type of stains you regularly encounter. 
Since I regularly encounter stains like ground-in baseball dirt and soccer grass, the best choice for me is liquid detergent, because it doubles as a stain removal pretreatment.
However, once all my little dirt devils are off to college, I'll be switching to powdered detergent - which is powerfully effective on general wash day challenges.
Unless, of course, I take up rugby in the interim.

what does detergent do, exactly?
Detergent works by loosening dirt and gunk from fabrics. Then it holds the removed dirt in the wash water until it can be rinsed away.
If you use too little detergent, clothes can become dull and dingy, white items may turn gray or yellowed, body soils are left on cuffs and collars, and lint isn't held in the water until it is rinsed away. Instead, it's redeposited on clothes.

You might also notice greasy looking stains because, if you regularly use too little detergent, it allows gunk to build up on the outer tub of the washer. These soils then wash off and redeposit on other loads. Ick. Err the other way.

1. the case for liquid laundry detergent.
Liquid detergent is especially effective on food and greasy or oily soils. Because it is fluid, it can double as a stain pretreated.
Choose liquid detergent if you do lots of spot-treating and have a family that specializes in food spills.

2. the case for powder laundry detergent.
Powder detergent is ideal for general wash-day loads. It's as effective in lifting out everyday stains as well as ground-in dirt.
If a majority of your family's laundry consists of stains of the outdoor and everyday variety, a powder detergent is an excellent choice.

3. how much laundry detergent should you use?
The answer varies by load. When reading the product directions, keep in mind that, because laundering conditions differ from home to home and from load to load, package recommendations should be considered only a starting point for determining proper amounts.

The amount of detergent you use will depend on:
• Water hardness (the harder the water, the more detergent needed), 
• The amount of soil in your load (more soil requires more detergent), and 
• The laundry wash temperature (cooler water requires more detergent).
The hotter the water, the more effective the detergent will be. When using cold water for washing, increase the amount of detergent to one-and-a-half to two times the recommended amount.

Source: http://www.clean-organized-family-home.com/