When you convert a measure of flour from grams to cups, you must take into account the type of flour you are using. There are seven basic types of flour: all-purpose flour, bread flour, plain flour, pastry flour, rice flour, self-rising flour, and whole wheat flour. Each of these has a different baking equivalent from grams to cups. Furthermore, the conversion changes based on whether the flour is sifted or not.
All-purpose flour is a blend of different types of flour. Hard and soft wheat flours are blended together to produce a flour with a medium protein content (10 to 12 per cent is average, although some brands use less). This makes it acceptable for baking a variety of goods, from cakes and cookies to breads and pastries. One cup of all-purpose flour is equal to 140g of unsifted flour, but you only need 115g if the flour is sifted.
Bread flour is used to make bread and certain pastries. Bread flour has a protein content of between 12 and 14 per cent and a higher gluten content, which helps the bread or pastry to rise. This also makes it more dense than all-purpose flour. As such, 1 cup of bread flour is equal to 160g unsifted, 130g sifted.
Plain flour, on the other hand, is much lighter than all-purpose flour. It has just 6 to 8 per cent protein content. In addition, it is usually chlorinated to help break down the gluten; this is what produces the rich, velvety texture unique to cakes. It also means that converting plain flour from grams to cups is a little different. With plain flour, just 130g of unsifted flour is required to make 1 cup, or 100g of sifted flour.
Pastry flour is very similar to plain flour; the main difference is that it has a slightly higher protein content (8 to 10 per cent), and it is not chlorinated. This is why pastry flour is more ivory in colour than white. The slightly higher gluten content makes it perfect for pastries, pies, and cookies. You need 135g of pastry flour to equal 1 cup.
Most self-rising flours have 8 to 9 per cent protein, but self-rising flour is well-suited to baking because of its additional ingredients. Self-rising flour is nothing more than all-purpose flour that has been blended with baking powder and salt, which reduces its protein content slightly by measure and makes your baking rise. To convert self-rising flour from grams to cups, take the 140g of flour as you would for all-purpose flour, and add 1½ tsp (7.5g) of baking powder and ¼ tsp (1.25g) salt.