While the classic mirepoix consists of 2 parts onions, 1 part carrots, and 1 part celery, feel free to adjust the ratio based on personal taste preferences and the dish you will add the veggies to. As noted in this tutorial, I prefer the mirepoix ratio set to 1 onion, 3 carrots, and 3 celery ribs for a flavorful base to add to any recipe.