Angee - I'm not quite sure what you're asking ... if you're wondering how you can tell what % of your current weight is fat and what % is muscle, the answer is that you need to have your body fat % measured. There are several ways to do this: underwater weighing (not practical for most of us), calipers, or bioelectrical impedance devices. To get your body fat % checked with calipers, you'll probably need to go to a gym - do you belong to one? There also are scales (Tanita makes some) and handheld devices that measure your BF with bioelectrical impedance. They're not totally accurate but can give you a sense of how your BF is changing over time. Online BF calculators using measurements are extremely unreliable and I personally wouldn't bother with them.
I'm not sure how your question about body fat and muscle ties in with running on the treadmill (which is awesome, by the way! Keep up the good work!
) Running is cardio exercise and is great for burning calories but won't build muscle for you. So running on the treadmill can't cause you to gain muscle weight. If you've gained weight, it could be that you're retaining water - sometimes sore muscles can make you temporarily hold water - or that you're eating more calories than you're burning off every day.
Weight loss boils down to calories in versus calories out. Running 1.3 miles at 5.2 mph (for example) burns about 150 calories. You have to create a 500 calorie deficit per day for a week to lose one pound (3500 calories) and a 1000 calorie deficit per day every day for a week to lose two pounds (7000 calories). If you're not losing at your current level of exercise, perhaps you need some additional exercise in order to lose some fat? The current government recommendations for weight loss are 60 minutes of exercise on most days.
Of course, a pound of muscle weighs the same as a pound of fat - a pound is a pound is a pound, right? - so please don't be confused if you hear people saying - oh, you've gained weight because muscle is heavier than fat. It's not!
But muscle IS smaller and denser than fat, so a pound of muscle takes up less space than a pound of fat. That's why building muscle while you lose fat will make you smaller, leaner, and tighter.
But the only way to build muscle is by lifting weights or using weight machines - unfortunately, cardio exercise - like running on the treadmill - won't do it.
Hope that helps! If I misunderstood your questions, please come back and clonk me over the head and I'll try to explain better.