By Teaspoon
Measuring a teaspoon is not only useful when you are cooking. They can also come in handy when you need to ensure you are slathering the optimal amount of slathering. And in fact, measuring sunscreen with a teaspoon may be the easiest way to do it. The recommended quantity when using a tea spoon which is equivalent to .04 ounces is ¼ teaspoon or 1/3 on the face.
Ilyas suggest using 1/3 teaspoon for effectiveness and extra protection, especially if you would be in a sunny area or if you are generally prone to sunburns.