So I'm trying to calculate the average surface pressure on Yih assuming the total mass of the atmosphere is the same as Earth. To find the total mass of the atmosphere, you multiply pressure by surface area and divide by surface gravity. Rearranging that to find the pressure, you multiply mass by gravity and divide by pressure.

Yih is slightly bigger than earth, though less dense. It has a radius 1.01 times that of Earth, and a surface gravity of 0.88g. I had to find the surface area, so plugged 1.01 into the formula for the area of a sphere, 4*pi*r^2, or if you prefer, as I do, 2*tau*r^2. I ended up with 12.8 and got really excited. Yih has 12.8 times Earth's surface area. So much room for activities! But no, I'm just running on 5 hours of sleep. It is 12.8… square earth radii. Yih's surface area is actually only 1.022 times that of Earth. That's only 749 Texases worth of extra room.

The pressure by the way would be 85100 pascals, or 0.8399 atmospheres. That's a bit higher than the typical air pressure in Denver. Water boils at about 203 freedom units, or 95 Celsius. I might up the O2 ratio to make sure the partial pressure is the same as Earth's though. I think I can figure out lapse rate, which would give me an idea how aeronautics plays out. The pressure at typical cruising altitude is around 200 hPa, which would be a fair bit lower on Yih.