First conver atm to N/m^2. 1 atm = 1.013 x10^5 N/m^2.

Force F=mg

The pressure is the force, gravity is 9.8 m/s^2, the diameter is in centimeters, so convert to meters and take half, you don't know m (mass).

The formula you use is P = F/A.

So you will have a formula that looks like

P = m (9.8 m/s^2) / radius

Plug in your numbers and the result will be in kg, which is the weight that can be lifted.