Neptune's atmosphere is sub-divided in two major regions, which are the lower troposphere and stratosphere. The boundary between the two occurs at a surface pressure of 0.1 bars, which is also 10 kPa. The stratosphere then gives way to the other region at a surface pressure lower than ten to five microbars.
clairedrom is likely correct, but it is likely that none of the gas giant planets especially Neptune have a liquid or solid surface. If they do, it's location is unknown, but we think the pressure will be extreme. Neil