When I use oz and when I use lb?!
Answers: In all cooking books I can see the default measure grams(g) but sometimes they write the g value in oz and sometimes in lb? Why?
There are 16 ounces (oz) in a pound (lb) so most American recipes will use ounces up to 1 lb and then change to pounds and fractions thereof. And we use cups and pints and their fractions for liquid measurements.
Probably for people who don't use the metric system.
It depends how much you're using. It wouldn't be practical to measure very small amounts in pounds; and if you need a pound of flour, that's more sensible than saying to use 16 oz.
Gram is a metric measurement commonly used in Europe and most the rest of the world. Ounce and pound are part of the American measurement system. So it would depend on where the recipe originated from what measurement you would see.