Physics made simple for everyone! Thank you Pip and Stormy for showing Pusheen how to easily understand! Details: Size: A6 (105 x 148mm / 4.1 x 5.8 inches). - that fits as a standard sized letter in the UK mail. Produced from sustainable sources and/or recycled materials Blank inside for your own message. 100% recycled brown kraft envelope supplied. Made in the UK.