HO gauge is a popular model railway scale that represents a ratio of 1:87. This means that one unit of measurement on the model corresponds to 87 units in real life. The track gauge, or the distance between the rails, measures 16.5 mm (0.65 inches), making it suitable for a wide range of layouts and settings. Due to its size, HO gauge is favored by both beginners and experienced hobbyists. It allows for detailed models of trains, buildings, and landscapes, making it easier to create realistic scenes. The scale's popularity has led to a vast selection of trains and accessories available in the market.