Hello!

As for me, the easiest way for such calculations is to do propotions.

For the example with cell number:

86.5*10^4 ------- 1000 uL ( it's your stock)

1*10^4 ------- X uL, so

X=(1000* 1*10^4)/86.5*10^4=11.56 uL

It means that 11.56 uL of stock contain 10^4 cells.

And example with DNA:

15 ng ------ 1 uL (stock)

40 ng ------- X uL, so

X = 40*1/15=2.67 uL.

So, you need 2.67 uL of stock solution, and adjust volume to 25 uL by adding 22.33 uL of buffer.

I hope, this explanation will help you!

Hello!

As for me, the easiest way for such calculations is to do propotions.

For the example with cell number:

86.5*10^4 ------- 1000 uL ( it's your stock)

1*10^4 ------- X uL, so

X=(1000* 1*10^4)/86.5*10^4=11.56 uL

It means that 11.56 uL of stock contain 10^4 cells.

And example with DNA:

15 ng ------ 1 uL (stock)

40 ng ------- X uL, so

X = 40*1/15=2.67 uL.

So, you need 2.67 uL of stock solution, and adjust volume to 25 uL by adding 22.33 uL of buffer.

I hope, this explanation will help you!

Dear Rs Rs:-

We can do that through calculating C1V1=C2V but in accurate measurement. That is the best way to calculate.

Hi there,

You don't have to use c1v1=c2v2 because in your case you are looking for a volume containing a given amount (of cells or of DNA) and not actually a final concentration. Therefore you are using the relationship between amount and concentration: n=c*v or v=n/c (where n stands for the amount, c for the concentration of the solution you have in hand and v for the volume of the solution).

In case of the DNA problem, you may actually use c1v1=c2v2 with c1=15ng/µL, c2=40ng/25µL=1.6ng/µL, v2=25µL. v1=c2v2/c1=40/15=2.67µL.

It's a cross multiplication thing. It is the best and easiest way. You just need to make sure to use the same units ml or µL or else you will have an error. Good luck.

Hi Rs Rs,

Using the formula C1V1=C2V2 is not technically wrong, but some times you may not need to dilute all of your stock cells you have. Very simple way to calculate the volume of cells you need from the stock is calculating the ratio of seeding density to stock density and multiplying it by the volume you need to seed. For example if you are aiming to have 50 ml of cells at 10 000 cells/ml seeding density from a stock of 100 000 cells/ml, then you need (10 000/100 000)*50 ml = 5ml of stock and dilute it with 45 ml of media.

I hope that will help you.

Also keep in mind that the result you get with the formula or using proportion/cross-multiplication, is just the amount( in uL or ng) of cells or DNA that you are looking for. When you add that amount to a new solution, the concentration will change.

For example, when you add the 40 ng of DNA to the solution with final volume of 25 uL, the final concentration of DNA will be :

40 ng DNA/ 25 uL total volume = 1.6 ng DNA/uL.

Now that you know the final concentration you need, you can use c1Xv1=c2Xv2 to calculate the volume of DNA you will extract from the stock solution, as long as you know the concentration of DNA in the stock solution. Let's say the stock concentration is 15 ng/uL as you mentioned:

c1Xv1=c2Xv2

15Xv1=1.6X25

v1=40/15

v1=2.67 uL

These are just different ways to get to the same answer!

As a post-doc once told me years ago as an undergraduate; divide what you want by what you have times the volume needed. The result is the volume of stock you will use and adjust to the final volume with media or solvent.

How I calculate the required number of cells to seed:

1. Count the number of cells using a hemocytometer

Say I counted 149 cells in 1 quadrant:

(149 x 10^4 cells/ml) divided by 1 (number of quadrants I counted) =

1.49 x 10^6 cells/ml

2. Then, to find out how many ml of these cells I need, I would go:

number of cells needed divided by number of cells I counted

So, say I need 2.5 x 10^6 cells per 10 mL dish

(2.5 x 10^6 cells) divided by (1.49 x 10^6 cells/ml) = 1.68 mL of cells needed.

3. Since I need 10 mL total. 10 ml - 1.68 mL cells = 8.32 mL media.

4. I would then add 8.32 mL of media and 1.68 mL cells. Resuspend, then add to the 10 mL dish.

For the DNA stock:

Yes, if the given stock is 15 ng/ul and you want 40 ng. Then you divide 40 by 15. This gives you 2.67 ul of stock DNA needed to have a total amount of 40 ng DNA. If you want this in 25 ul total, simple go:

25 ul - 2.67 ul DNA = 22.33 ul total water to add.

This will give you a total concentration of: 40 ng/25 ul = 1.6 ng/ul

Hope this helps.