Slot Cars and slot car tracks come in many sizes. The 4 most common sizes are 1/64 (Small), 1/43 (Medium), 1/32 (Large), and 1/24 (XL). The size of the track and cars you purchase should depend on how much room you have to setup the track and what aspects you are looking for in the cars and track itself. The most popular tracks for home use are 1/64 and 1/43.
1/64 cars are also known as HO. With a size of around 2.5 inches, they are the most popular and smallest size of the slot car family. Choosing to go with a 1/64 slot car set will mean you will be able to fit more track in a small area. This will allow for more turns, more track, and a greater journey. Because of their light weight, HO or 1/64 cars can do loops and obstacles that larger cars can not perform. Another benefit of purchasing a 1/64 scale track is you can easy find 2 and 4 lane options. 2 lanes are perfect for smaller areas, while 4 lanes are great for larger groups or families. One downside of 1/64 cars is, because of their small size, they will be less detailed.
If you are looking for a track to fit in a small area, but would also like the cars to have good detail then a 1/43 size track would be a good choice. These cars are 3-4 inches long. The cars are light enough to do loops and small enough to fit many curves in a small area. They are large enough to display racing decals, door handles, and other detail. 1/43 cars are newer to the hobby, so there are far less cars and tracks available then at the 1/64 scale, but the are becoming increasingly popular. This is a good track option for kids and the Carrera “Go” brand has many cars that have been designed for kids, such as Disney Cars and Spiderman.
1/32 slot cars are still small enough for home use, but require quite a bit more space than the smaller cars. They are 5-6 inches long and are very detailed. These cars are too heavy to do loops, but are very fun due to their larger size and more realistic appearance. 1/32 slot cars are not new to the hobby and they are many tracks and cars available. These cars have many options for customization. You can upgrade tires, gears and motors if you choose to, but the cars almost always come ready to race. 1/32 slot cars look great on a display case or shelf when they are not racing.
1/24 cars are large. They are usually 7-8 inches long. These cars are normally raced on club and commercial tracks. It is possible to have a track at home, but it would likely take up a whole room. Because of the large size of these cars, they are very detailed. These cars can be customized by adding new tires, a new motor, new gears, etc… Many hobbyists build 1/24 slot cars from parts and can become a slot car mechanic when their cars crash.