BTU Calc helps you find the right air conditioner or heater size for any room before you buy. Enter the room length, width, and ceiling height, then select whether you need cooling, heating, or an all-season unit. The app factors in sun exposure (shaded, average, or sunny) and your climate zone (mild, mixed, hot summer, or cold winter) to compute both cooling and heating loads. It then rounds up to the nearest standard BTU size and shows the equivalent tonnage so you can shop with confidence. Save multiple named room scenarios, compare results side by side, and keep a history of past calculations.