Cell Dilution Calculator

Every culture dilution conserves the total number of cells, meaning the product of concentration (C) and volume (V) stays constant. This calculator rearranges $C_1 V_1 = C_2 V_2$ so you can solve for the missing stock concentration, inoculum volume, final concentration, or final volume without rewriting algebra on a lab bench.

How the conversion works

The basic relationship is:

$$C_1 V_1 = C_2 V_2$$

Provide any three of those values and the tool solves for the fourth. For example, to find the aliquot $V_1$ needed to seed a target $C_2$ and $V_2$, use $V_1 = \frac{C_2 V_2}{C_1}$. Results are returned in whichever units you select (mL or L for volumes, any concentration unit such as cells/mL).

Units and conversions

Worked examples

1. Tenfold dilution
   Pipette 1 mL from a $1.0 \times 10^7$ cells/mL stock into a tube and bring to 10 mL.

$$C_2 = \frac{1.0 \times 10^7 \times 1}{10} = 1.0 \times 10^6\ \text{cells/mL}$$

2. Seed a bioreactor charge
   You need 50 mL at $8.0 \times 10^5$ cells/mL and the inoculum is $5.0 \times 10^6$ cells/mL.

$$V_1 = \frac{8.0 \times 10^5 \times 50}{5.0 \times 10^6} = 8\ \text{mL}$$

Add diluent until the vessel reaches 50 mL, yielding the target density.

Tips and pitfalls

• Record all units; mixing mL and L without conversion throws the math off by 1000x.
• Adjust for dead volume in pipette tips when planning micro-scale serial dilutions.
• When chaining serial dilutions, multiply dilution factors rather than repeating full calculations.
• Keep stock concentrations updated with cell counts to avoid using stale numbers.

References and further reading

• Freshney R.I. - Culture of Animal Cells
• Thermo Fisher Scientific - Serial dilution basics