Ok, so you want to seed 5 wells at each confluence. Let's calculate for 7, then. Generally, prepare your suspensions in a tube off of the plate first, then seed the resuspension onto the plate at the final dilution. (Not cells first, then medium).

Ok, so 7 wells at 200 uL per well will be 1.4 mL. This will be the final volume of your suspension before seeding. You can do this in a 2 mL tube with comfortable space.

7 wells at 12,000 cells per well is 84,000 cells. This is the number of cells from your concentrated original stock to the 2 mL tube.

You have 2,400,000 cells in 10 mL, which comes out to 240,000 cells per mL. By simple division this is (84,000 cells) / (240,000 cells/mL) = 0.350. The units cancel to mL, or 0.35 mL, which is 350 uL.

So, to get 84,000 cells, which is the number of cells needed if you evenly distribute your suspension across 7 wells for a final of 12,000 cells per well you need to dilute up 350 uL of cells from your original stock.

We know you need 1.4 mL of final suspension, so 1.4 mL - 350 uL = 1050 uL of medium to adjust the volume.

Take a 2 mL tube:

• Add 350 uL of cells
• Add 1050 uL of medium
• Mix will
• Dispense 200 uL per well into a 96-well plate for 12,000 cellls/well
• You will have excess, discard or re-seed into a flask to conserve

Rinse and repeat for all concentrations you want.

As Jordan said you have a 240,000 cells per ml (cells/ml). You can dilute the cell suspension 1:3 (add 1 ml of cell suspension to 2 ml of medium). In this way you will have 3 ml of cell suspension with a concentration of 80,000 cells/ml (240,000:3= 80,000).

To plate 16,000 cells: Add 200 ul per well 

(16,000 cells divided 80,000 cells/ml = 0.2 ml = 200 ul )

To plate 12,000 cells: Add 150 ul per well + 50 ul of cell medium

(12,000 cells divided 80,000 cells/ml = 0.15 ml = 150 ul )

Thanks so much for both of your guys' help!

I'd like to give update for others needing help with seeding densities of a new cell line for their lab. I ended up doing a cell count and plating a range of cells (5000, 7500, 10,000, 12,500, 15,000, 20,000, etc). The next day, I checked the confluency of each to see what seeding amount gave me the confluency I needed, and wrote down the rest because some other protocols call for different confluency percentages. Hope this helps anyone else having issues.