When pasta, oats, quinoa, and other types of dry grains are cooked, they soak up water, expand, and ultimately end up weighing much more. For example, ½ cup of dry oats might weigh about 40 grams before cooking, but after cooking it will weigh closer to 80 grams and fill up an entire cup.
The caloric density of a food decreases as water content increases (and vice-versa). Raisins are a great example of this—when you remove the water from grapes, you get a calorie dense dried fruit! The grape may have weighed a few grams, but after it is dehydrated to become a raisin, it has the same calorie and macro value but is probably less than half its starting weight.
To eliminate error caused by cooking grains and adding an unspecified amount of water weight, it’s best to weigh your grains dry and before cooking them.
For more info, check out our blog post The Simple Guide To Measuring Your Food In Grams.