I have read other modest fashion blogs and they have different standards for modest clothing. Some define modest by just covering their bodies even if the clothes are tight. Some shows only the face and the rest are fully covered with loose-fitting clothes. I also have my own standard for a modest outfit:
1. Cleavage is not exposed. Place your hand in a horizontal position with your pinky finger just above your cleavage and all 5 fingers side by side. The portion up to your thumb is the lowest neckline that you can have.
2. Sleeves should be at least half-way between your shoulder and elbow.
3. Length of the blouse should be such that your lower back does not show when you sit or in a horizontal kneeling position.
4. Blouse is not tight. Chest area should be more than the size of your bra. People need not to know by looking at your blouse that your size is 35 cup B. If any of the gaps between buttons opens, whether you are in a straight or slouching position, your blouse is tight. Using a pin to close it is still inappropriate because the blouse itself is tight.
5. Ideal skirt length is 3 to 4 inches below the knees. If you are tall, it should cover at least half of your leg.
6. Skirt is loose-fitting especially around the butt area. Avoid cloths that will make your panty line visible.
7. Pants are allowed as long as they are loose-fitting. They should not hug your thighs tightly when sitting down. Length should be the same as the allowed length for skirts and should be paired with a long blouse that fully covers the hips, butt, and crotch areas.
These guidelines are my minimum set criteria of a modest outfit but could be more. If you are really into modest clothing, you can judge your overall outfit by looking at the mirror to see if it is appropriate and will not cause sinful thoughts to men.