A sheet of A5 paper measures 14.8 cm by 21cm. This means an A5 sheet covers an areas of 310.8 cm squared.
All paper sizes around the world, with the exception of North America, follow ISO 216 measurements. ISO stands for the International Organization for Standardization and is based in Switzerland. ISO promotes and regulates the use of measurements in over 160 countries, primarily for business and industry purposes.
Other ISO Recognized Paper Sizes Include:
A2: 42 cm x 59.4 cm
A3: 29.7 cm x 42 cm
A4: 21 cm x 29.7 cm
A6: 10.5 cm x 14.8 cm
A7: 7.4 cm x 10.5 cm
To learn more about ISO 216 paper sizes, take a look at this video: