basic question on passage ratios - (Aug/20/2010 )

Hello all,

I'm an undergrad student new to tissue culture and just had a simple question on passaging cells. I am using 15 cm plates for my cells with a total of 20 ml of media + cells that are allowed on the plate and am confused on the cell passage ratios. The first time the grad student showed me it was a 1:10 split in which I took 2 ml of the cell suspension (of which I took 10 ml complete media, added 8 ml of that to a plate w/ 2 ml trypsin and repeated for second plate) and then added 18 ml complete media to a total of 20 ml per plate. She then asked me a couple days later to split the cells 1:5 so that I had 10 plates total but did not elaborate on how much of the cell suspension I should have per plate or how to correctly calculate the split ratio. Can anyone offer any advice on the simplest way to calculate the passage ratio such as 1:5 or 1:2 so that I know how much of the cell suspension I should add per plate?

I've been trying to ask the grad student but she's in the middle of writing her dissertation and has become quite busy so any help is appreciated. Thanks!

1:5 means that you divide the cell volume you have by 5 and add one part to a new plate/well/flask... and is completely independent of the volume you are adding it to.