How do you know when to change your pad?

You can normally wear a pad for 3-4 hours on average, depending on flow. If the pad looks saturated on the underside, it doesn't mean that it is going to leak. That is just the absorbent lining of the pad drawing the fluid into its core. Usually, with pads, you start to feel a dampness that doesn't go away. You know that gushing feeling you get when your period comes out and it feels wet immediately afterward, but then it goes away? It's like that, but then it stays wet. That is when you need to change. Also, be aware of odors and change if you notice one. Good Luck!