How the math works
Every number on this page comes from these formulas — nothing is estimated or looked up.
The core law: C₁V₁ = C₂V₂
Diluting never creates or destroys cells, so the number of cells you pipette out of the stock equals the number of cells in the final tube:
C₁ · V₁ = C₂ · V₂ → V₁ = (C₂ · V₂) / C₁
with C₁ = stock concentration, C₂ = target concentration, V₂ = final volume, V₁ = stock volume to pipette. The diluent (medium/buffer) volume is simply V₂ − V₁.
Dilution factor
DF = C₁ / C₂ = V₂ / V₁
A 20× dilution means the stock is 20 times more concentrated than the target, written 1:20 — one part stock in twenty parts total. Pipette 1/DF of the final volume as stock (for 20×: 5% of V₂).
Serial dilutions multiply
When one step would need an un-pipettable volume (below ~10 µL), split the dilution into steps. Dilution factors multiply:
DFtotal = DF₁ × DF₂ × … × DFn
Three 1:10 steps give 10 × 10 × 10 = 1000×. The planner above finds the shortest exact split where no step exceeds your pipette-friendly cap, folding any fractional remainder into the last step so the final concentration lands exactly on target.
Unit conversions used
1 cells/µL = 1,000 cells/mL (1 mL = 1,000 µL)1 million/mL = 1,000,000 cells/mL1 cells/L = 0.001 cells/mL
Scope honesty
This tool does dilution math only. It does not count cells (use a hemocytometer or automated counter for that), does not model cell viability or growth, and does not replace your lab's SOP. Looking for molarity (mol/L), mg/mL, %, or ppm dilutions? This tool handles cell concentrations only (cells/mL, cells/µL, million/mL) — chemical C₁V₁=C₂V₂ belongs to a dedicated chemistry dilution tool. Always double-check the pipetted volume against your protocol — especially below 10 µL, where this calculator warns you and suggests a serial dilution instead.
Frequently asked questions
How do you calculate a cell dilution?
The standard formula is C1V1 = C2V2: stock volume to pipette V1 = (C2 x V2) / C1, where C1 is your stock concentration, C2 the target concentration, and V2 the final volume. Example: from a 2x10^6 cells/mL stock to 1x10^5 cells/mL in 10 mL, pipette (1x10^5 x 10) / 2x10^6 = 0.5 mL of stock and add 9.5 mL of diluent. The calculator above does this instantly and shows every step.
What is the dilution factor in cell counting?
The dilution factor (DF) is how many times more concentrated the stock is than the target: DF = C1 / C2, which also equals V2 / V1. A 20x dilution means the original is 20 times stronger. In cell counting it is often written as a ratio, 1:20, meaning one part stock in twenty parts total volume.
How do you calculate the dilution factor for cell counting?
Divide the stock concentration by the target concentration: DF = C1 / C2. For example, diluting 2x10^6 cells/mL down to 1x10^5 cells/mL gives DF = 2x10^6 / 1x10^5 = 20, i.e. a 20x (1:20) dilution. When you dilute with a hemocytometer-style fixed ratio, DF also equals total volume divided by the transferred volume.
What is the formula for dilution factor?
DF = C1 / C2 = V2 / V1, where C1 and C2 are the stock and target concentrations and V1 and V2 the stock and final volumes. Written as notation, a dilution factor of 20 is expressed 1:20. The fraction of the final volume that must be pipetted as stock is simply 1/DF - for a 20x dilution, 5% of the final volume.
How do you dilute cells to a desired concentration?
Follow four steps: (1) measure or look up your stock concentration C1; (2) decide the target concentration C2 and final volume V2; (3) compute V1 = (C2 x V2) / C1 - that is how much stock to pipette; (4) add diluent (medium or buffer) up to V2, i.e. V2 - V1. Mix gently but thoroughly, since cells settle fast. If V1 comes out below about 10 uL, split the job into a serial dilution instead of pipetting an unreliable micro-volume.
How do you dilute a cell suspension for counting with a hemocytometer?
For counting, you typically want roughly 20-100 cells per large hemocytometer square, which for most cultures means diluting into the 1-5x10^5 cells/mL range. Use C1V1 = C2V2 to work out the transfer volume, then mix the diluted sample 1:1 with trypan blue (remember that halves the concentration again - a further 2x factor). The final concentration is: (cells counted / squares counted) x 10^4 x dilution factor.
What is the difference between cell concentration and cell density?
They describe the same physical quantity - cells per unit volume - but are used in slightly different contexts. Cell concentration (cells/mL, cells/uL) is the precise lab term used in calculations like C1V1 = C2V2. Cell density is the looser, everyday term for how crowded a culture looks, sometimes expressed per area (cells/cm2) for adherent cultures. For suspension dilutions, treat them as interchangeable.
How do you plan a serial dilution of cells?
A serial dilution chains several small, accurate dilutions whose factors multiply: three 1:10 steps give 10 x 10 x 10 = 1000x total. Decide the total factor you need (C1/C2), then split it into steps no larger than what you can pipette accurately - 10x to 100x per step is typical. The Serial dilution planner tab above finds the shortest exact scheme automatically and prints the transfer and diluent volume for every step.
By what ratio is cell density reduced in each step of a serial dilution?
By exactly the dilution factor of that step: a 1:10 step divides the density by 10, a 1:100 step by 100. Because factors multiply across steps, a 1:10 followed by a 1:100 reduces the starting density 1000-fold. That is why serial dilution is the standard way to reach very low concentrations - each step stays in a pipette-friendly volume range while the total factor compounds.
What is cell seeding concentration and how do you calculate the dilution?
Seeding concentration is the target density at which you plate cells, e.g. 1x10^5 cells/mL or a fixed number of cells per well. The dilution math is identical to any other dilution: V1 = (C2 x V2) / C1. For example, to seed 2 mL per well at 2x10^5 cells/mL across 6 wells (12 mL total) from a 1.5x10^6 cells/mL stock: V1 = (2x10^5 x 12) / 1.5x10^6 = 1.6 mL of stock plus 10.4 mL of medium.
What if my target concentration is higher than my stock?
Then you cannot dilute - dilution only lowers concentration. This calculator refuses the calculation and tells you so, instead of silently producing nonsense. Your options are to concentrate the cells (centrifuge and resuspend in a smaller volume), grow the culture longer, or start from a denser stock.
What should I do when the volume to pipette is too small to pipette accurately?
Do not pipette it - pipetting under ~10 uL in one step introduces large relative error. Make a serial dilution instead: for example, rather than pipetting 0.5 uL directly, do a 1:100 step (10 uL into 990 uL) followed by a 1:20 step. This calculator warns you automatically whenever V1 drops below 10 uL and the Serial dilution planner tab builds the exact multi-step alternative.
How do cells/uL, cells/mL, and million/mL convert?
1 cells/uL = 1,000 cells/mL (because 1 mL = 1,000 uL), and 1 million/mL = 1,000,000 cells/mL. So 2,000 cells/uL is the same as 2x10^6 cells/mL, which is the same as 2 million/mL. The unit selectors in the calculator convert automatically - just pick the unit your counter or protocol reports.
How does this compare to the OmniCalculator cell dilution calculator?
OmniCalculator's cell dilution page covers the basic C1V1=C2V2 calculation in a single thin box. This calculator adds what a bench workflow actually needs: an exact serial dilution planner that finds the shortest pipette-friendly scheme, show-your-work for every step, four concentration units and three volume units, an honest sub-10-uL pipetting warning, an honest refusal when the target exceeds the stock, and three hand-checked worked examples - all computed 100% in your browser with no data sent anywhere.