Emergency tent sizes are numerous. They are generally available in 2-person, 3-person, 4-person etc sizes. These are the same dimensions as those of camping tents.
This will depend on how many people are going to use the tent. If you are the only person who is going to use it, the one-person size will be sufficient. If you plan to bring a lot of camping gear, buy the 2-person tent.
You can use the extra space for the equipment. For four people or more, you should get the family size. There are even tents for 8 people or more. If you camp alone, the 2-person tent will be enough. A bigger tent will be hard to carry around.
The emergency tent sizes aside, you should take packing into consideration. The structure should be easy to set up. Some tents are very hard to set up when the wind is blowing. A well designed tent should be easy to set up regardless of the size.
Some tents use very flimsy material. Others look like mosquito nets. The stronger types are made of polyester or canvas. These are the strongest and most suitable for emergencies. But they are heavy. But tents are necessary even if you are just backpacking. After hiking all day, nothing is more relaxing than cozying up inside a tent.
For Emergency Uses
Of course the primary purpose of these tents is to provide shelter during an emergency. Nobody wants to think of emergency situations. But in case a hurricane, tornado or natural calamity makes your house uninhabitable, this is the best option. You will also see these tents used in refugee camps and in calamity stricken areas.
Make sure you get a quality tent. The good ones are going to cost you, but they are durable. In the event of a disaster, a durable tent is a must. If you are looking for a backpack tent, the size will be more important.
If you live in a rural area, you can set up a large tent anywhere. If you live in a city, finding a good spot will require travel. You may opt for several small tents instead.
You also want a an emergency tent size that is comfortable. These are going to cost some money, but they will be worth it. Nothing is worse than cramming yourself in an uncomfortable shelter. Being in a cozy shelter during a calamity / crisis will help.