Summarize:

The Humane Society of the United States has noted that most cages available on the market for guinea pigs are simply too small. In fact, most cages are instead meant to house smaller animals like hamsters and gerbils.  Unlike other animals, guineas pigs need floor space, not vertical space. They need ample room to move around and exercise in order to stay healthy. A cage that is too small for a guinea pig can cause the animal to become bored and depressed. Imagine if you had to spend your entire life living in a closet with little room for activity and stimulation. Guinea pig cages that are too small have also been linked to the development of certain medical conditions. They are more likely to get pododermatitis (the equivalent of bed sores, but on their hocks) as a result of sitting still on soiled bedding. Larger cages are also better if you have more than one guinea pig so that each pet can have its own personal space. Larger cages also have benefits for you as well! They're easier to clean because they enable guinea pigs to separate their "bathroom" space from their other living areas. Typically, the recommended standard cage size is about 2 square feet per guinea pig. However, this is insufficient, as there is not enough room for everything a guinea pig needs, including food, water dish, nest, and bathroom area. Guinea Pigs need more room than other animals, because they cannot use the running wheels. Instead, they need space to exercise. Consider the following guidelines, which provide more space and consider the number of pigs in the cage:   1 guinea pig -  7.5 square feet (0.75m2) minimum size. More is advised. Aim for a cage that is 30" x 36" (75cm x 100cm)  2 guinea pigs - 7.5 square feet  (0.75m2) cage (minimum). However, 10.5 square feet (1m2) is advised. Aim for a cage that is 30" x 60” (75cm x 150cm).  3 guinea pigs - 10.5 square feet (1m2) cage (minimum). However, 13 square feet (1.25m2) feet is advised. Look for a cage that is 30" x 76” (75cm x 190cm).  4 guinea pigs - 13 square feet (1.25m2) cage (minimum). However, more space is advisable and you should look for a cage about 30" x 90” (75cm x 225cm). Where you place the cage in your home is very important. For sanitary reasons, avoid keeping the cage in or very near to the kitchen. You'll need to consider several factors in order to determine the right spot, including:   Temperature - Make sure to keep your guinea pig cage away from extreme temperatures because the animals don't like very cold, warm and humid temperatures and can become ill. The ideal temperature for a guinea pig cage is about 65-75℉ (18-24℃). Keep the cage away from drafty spaces like doors and windows and place it on an elevated surface.   Activity - Guinea pigs enjoy being near family activity and benefit from more attention when they’re easy to see and hear. A family room or living room works well, but make sure your pigs have a place to retreat if they need some quiet time.   Noise - Guinea pigs have very sensitive hearing and their cages should not be placed next to stereos, televisions or other loud noises. Put the cage in an area in your home where you can supervise interactions between your children and the guinea pig so that your guinea pig does not escape or get injured. Similarly, keep your pig safe from any pets (especially cats and dogs) by keeping the cage inaccessible to curious pets. Some people choose to keep guinea pigs indoors, where they are safe from extreme weather and predatory animals, while others prefer to keep them in outdoor hutches. If you choose to keep your guinea pig indoors, attempt to get your pet out into the sunshine regularly to aid Vitamin D synthesis for healthy bones and teeth. If you have an outdoor hutch, the guinea pig requires daily attention from the owner. Bring your pet inside in extremes of weather. In addition, guinea pigs are social animals and thrive when they are able to interact with humans. Keeping them outdoors limits opportunities for daily socialization.
Consider the size of the cage. Follow the appropriate size guidelines. Think about the location of the cage in your home. Keep the cage safe from children and other pets. Choose a safe spot either inside or outside.