When indoor humidity starts causing problems—musty smells, condensation on windows, or even mold—your first move might be to shop for a dehumidifier. But before do, you need to answer one key question: “What size dehumidifier do I actually need?”Dehumidifiers reduce humidity levels by drawing in moist air, removing the moisture, and releasing drier air back into the room. Choosing a dehumidifier with the right capacity isn’t just about the square footage of your room or home. It's also about how much moisture the unit can remove from the air. Start With Square FootageTo pick the perfect dehumidifier, the first step is to measure the area where you intend to use it.