Aeropress FAQ:

"The AeroPress filter is 2.5 inches in diameter so the area of the filter is 4.9 square inches. If you press down firmly on a scale, it is relatively easy to get the scale up to 25 pounds and then if you press hard on the scale, you can certainly get it up to 50 pounds. Therefore if you press similarly hard on your AeroPress while brewing coffee, the firm pressing will be at 5.1 psi (25 lbs/4.9 sq in) and the harder pressing will be at 10.2 psi (50 lbs/4.9 sq in). Since a bar of pressure is 14.7 psi, the former is .35 bar and the latter is .70 bar."

https://www.aeropress.co.uk/pages/faqs

See also James Hoffman's experiment:

https://youtu.be/jBXm8fCWdo8?t=976