What kind of cereal? Cereal can be super high in calories depending on what kind it is and you might be surprised to see what kinds are highest in calories. Like some cereals may be 400 calories for 2 cups, which for me would be like 1/4th of my daily calorie goal and I'm not really trying to lose weight super fast. (If I were it would be closer to 1/3 my daily calorie goal because I'm so short)
Also, invest in a food scale for more accurate measurements. Measuring cups can help get you close but some foods can surprise you, and some things are almost impossible to really portion out properly without a food scale. $20 should be enough to get a decent one if you look on Amazon.
CICO (Calories in, Calories Out) is really all that matters for weight loss. That doesn't necessarily mean you have to count calories, but if you are eating fewer calories than you are burning you will lose weight, it's as simple as that. For some people eating low fat/low carb/low whatever is the easiest way to eat at a calorie deficit, but for me just counting calories has always been the easiest because I can eat literally anything I want as long as I budget the calories for it. You can calculate how many calories you burn every day here, and just aim to eat below that. I use myfitnesspal.com to track what I eat every day.