A gram is equal to exactly 0.03527396195 ounces. For practical everyday purposes, a rounded figure of 1 gram to 0.035 is used. Thus, there are 7 ounces in 200 grams (200 x 0.035).
Ounce is a unit of mass in the imperial system. This system of units is also know as British Imperial. At present, the imperial system is commonly used in the USA and in other nations that were once part of the British empire.
Gram is the metric system's unit of mass. The modern form, and currently the most widely used in the world, of the metric system of units is the International System of Units, or SI.