So I'm working on a chemistry lab determining Avogadro's constant with a fatty acid monolayer on a beaker of water, and my calculations are all work out to around 1.3*10^23 (ie a sixth of what they should be). The lab said "fill the beaker with water until it spills over". In doing so, I ended up with a large curve in the surface of the water. However, the lab guidelines don't explain any way to account for that (I assume they wanted the water at 90° to the beaker). Does anyone know of a formula to find the maximum surface area of water that includes the effects of surface tension? The surface tension is the only error I can think of that can be fixed in my report (other stuff, like adding too many drops stearic acid I'm stuck with...).